12 September 2026

Now Put Linux to Work — Build Your Own Web Server on a Raspberry Pi

Learning Linux commands is useful.

But there comes a point when simply moving files around, listing directories and installing packages stops feeling like a project.

So now that we have discovered Linux, it is time to make Linux actually do something.

One of my favourite first projects is surprisingly ambitious:

Build your own web server and host a website from your own Raspberry Pi.

You can start with a blank Raspberry Pi, type a handful of commands into the terminal and, a short while later, open a browser on another computer and see a web page being delivered by the Pi.

Then comes the really interesting possibility.

With some additional configuration, that little computer sitting on your desk can serve a website to somebody hundreds or thousands of miles away.

At that point Linux suddenly stops being an operating system you are studying.

It becomes part of the Internet.

What Exactly Is a Web Server?

When you visit a website, your browser is not normally downloading pages from some mysterious thing called "the Internet".

It is communicating with another computer.

Your browser sends a request.

The remote computer receives that request and sends something back — perhaps an HTML page, an image, some JavaScript or data.

The program performing that job is the web server.

Popular web-server packages include Apache and Nginx.

For this project I am going to use Apache, partly because it is extremely well established and partly because it makes a very approachable first Linux server project.

Raspberry Pi OS is based on Debian Linux, which means software can be installed using Debian's package-management system. The current Raspberry Pi OS is based on Debian, making standard Linux server tools readily available.

Why a Raspberry Pi Is Such a Good Server Project

A Raspberry Pi is not going to replace the enormous server infrastructure used by Amazon, Google or Microsoft.

That isn't the point.

For a small personal website, school project, development server, experimental dashboard or home intranet, it is remarkably capable.

More importantly, it allows students to see several areas of computing come together at once.

Suddenly we are dealing with:

Linux commands and file systems;
HTML and CSS;
IP addresses;
client-server computing;
TCP/IP networking;
ports;
DNS;
permissions;
services and processes;
cybersecurity;
remote access.

That is why I like this project so much.

We are no longer learning these ideas as isolated examination topics.

We are building something in which they all have a purpose.

Step 1 — Start With Your Raspberry Pi

You need relatively little equipment:

A Raspberry Pi running Raspberry Pi OS, a microSD card or SSD, a network connection and access to a terminal.

You can use the full Raspberry Pi OS desktop or Raspberry Pi OS Lite.

For a dedicated server, Lite is particularly interesting because it has no graphical desktop. You are interacting with the machine almost entirely through the command line.

That initially feels like a disadvantage.

It quickly becomes part of the attraction.

You begin to realise that a server doesn't actually need a screen, keyboard or mouse permanently attached to it.

It just needs to be running.

Step 2 — Update Linux

Open the terminal and begin with:

sudo apt update
sudo apt upgrade -y

There are several useful Linux ideas contained in those two commands.

sudo means we are running the command with elevated administrator privileges.

apt is the package-management system.

update downloads current information about available packages.

upgrade updates software already installed on the machine.

This is a good habit before installing new server software.

It is also an opportunity to discuss something that is sometimes missed when students study operating systems:

software maintenance is part of running a computer system.

A server that works perfectly but is never updated eventually becomes a security problem.

Step 3 — Install Apache

Now comes the wonderfully satisfying part.

Type:

sudo apt install apache2 -y

That is essentially it.

Linux downloads Apache, installs the necessary files and configures the web-server software.

You can check it with:

systemctl status apache2

You should see that Apache is running.

The systemctl command gives us another useful Linux concept.

Apache isn't simply a program we have opened in a window.

It is running as a service.

The server can start automatically when the Raspberry Pi starts and continue running quietly in the background.

That is how much of Linux server administration works.

Step 4 — Find the Raspberry Pi's Address

Every device on your home network needs an IP address.

Try:

hostname -I

You might see something resembling:

192.168.1.74

The exact address will be different on different networks.

Now go to another computer, tablet or phone connected to the same network and enter:

http://192.168.1.74

using your own Pi's address.

If everything has worked, something rather wonderful happens.

A web page appears.

It isn't coming from Google.

It isn't coming from a web-hosting company.

It is coming from the Raspberry Pi sitting beside you.

The Raspberry Pi Foundation has long used essentially this kind of Apache experiment as an introduction to hosting local HTML pages on a Pi.

Pause Here — Because Something Important Has Happened

This is a moment worth thinking about.

We installed some software.

The software opened a service listening for web requests.

Another machine found the Raspberry Pi using its IP address.

A browser sent an HTTP request across the network.

Apache received it.

Apache located an HTML document.

Apache sent the document back.

The browser interpreted the HTML and displayed the result.

We have just constructed a genuine client-server system.

Suddenly those network diagrams found in computing textbooks make considerably more sense.

Step 5 — Replace the Default Page With Your Own Website

The standard Apache website files are normally stored in:

/var/www/html

Go there:

cd /var/www/html

Have a look:

ls

You should find an HTML file.

We can replace it with our own page.

For example:

sudo nano index.html

Then create something simple:

<!DOCTYPE html>
<html>
<head>
    <title>My Raspberry Pi Server</title>
</head>

<body>
    <h1>Hello from my Raspberry Pi!</h1>

    <p>This webpage is being served by a computer in my house.</p>

    <p>I built this server using Linux and Apache.</p>
</body>
</html>

Save the file.

Refresh the browser.

Your page appears.

There is something particularly satisfying about this because we can immediately see the result of what we have done.

Now Make It Look Like a Proper Website

The next stage is obvious.

Add some CSS.

Create several pages.

Add photographs.

Build navigation.

Perhaps create:

index.html
about.html
projects.html
contact.html

You could create folders for:

/images
/css
/javascript

Now our Linux project has naturally become a web-development project as well.

A student who has learned some HTML and CSS can suddenly host what they have created on a real server rather than simply double-clicking an HTML file on their computer.

That difference matters.

Try Talking to the Server Without a Browser

There is another lovely Linux experiment we can perform.

On the Raspberry Pi type:

curl http://localhost

Instead of beautifully formatted text and pictures, you should see the HTML returned directly to the terminal.

Why?

Because curl is acting as the client.

The browser isn't essential.

This is an excellent demonstration of the difference between the data returned by the server and the way a browser interprets that data.

Look Behind the Scenes

Once a student has a working server, there is plenty more to investigate.

For example:

sudo systemctl restart apache2

restarts the server.

You can look at Apache's log files:

cd /var/log/apache2

and examine requests arriving at the server.

One particularly interesting command is:

sudo tail -f /var/log/apache2/access.log

Leave that running and visit your website from another device.

Requests begin appearing.

Refresh the browser.

Another request appears.

Visit another page.

Another appears.

This is the Internet becoming visible.

A website visit that seems almost instantaneous from the user's side is actually producing identifiable network activity on the server.

A Great Networking Investigation

There is an excellent experiment you can perform before going anywhere near the public Internet.

Try accessing the Raspberry Pi from:

the Raspberry Pi itself;
another computer connected by Ethernet;
a laptop connected by Wi-Fi;
a phone connected to your home Wi-Fi;
the same phone after switching Wi-Fi off.

The first four may work.

The fifth probably will not.

Why?

Because something fundamental has changed.

The phone is no longer part of your local network.

And that introduces one of the most important distinctions in networking:

a private IP address is not the same as a publicly reachable Internet address.

So How Do We Put the Website on the Internet?

This is where the project becomes even more interesting.

Inside your house, your Raspberry Pi might have an address such as:

192.168.1.74

That is a private address.

Millions of networks can use addresses like that.

Someone elsewhere on the Internet cannot simply type that address and arrive at your Raspberry Pi.

Traditionally, we solve this using technologies including:

NAT, port forwarding, DNS and a public IP address.

A home router can be configured so that requests arriving on particular ports are forwarded to your Raspberry Pi.

Web traffic commonly uses:

Port 80 = HTTP
Port 443 = HTTPS

You might also register a domain name so that people visit something meaningful such as:

www.myexperimentalsite.co.uk

rather than remembering an IP address.

Suddenly DNS — another subject that can seem rather abstract when taught from a diagram — has a very obvious purpose.

But Don't Simply Open Everything on Your Router

This is also where the project gives us an important lesson in cybersecurity.

Putting a server onto the public Internet means computers anywhere in the world can attempt to communicate with it.

That means we need to think about security before simply opening ports.

At a minimum, a public server should be kept updated, unnecessary services should remain closed, administrator accounts should use strong authentication, remote SSH access should preferably use keys rather than passwords, and a public website should use HTTPS.

Raspberry Pi's own current security guidance recommends key-based authentication for improving SSH security and also discusses tools such as Fail2Ban for systems operating as servers.

This is another reason this project is so valuable.

Cybersecurity stops being a theoretical discussion about "hackers".

The student now owns a machine that may potentially be reachable from the Internet.

The question becomes:

What exactly am I exposing?

A Modern Alternative — Use a Secure Tunnel

There is another approach that I think is particularly interesting for an educational project.

Instead of opening incoming ports on your home router, services such as Cloudflare Tunnel can create an outbound connection from the Raspberry Pi to a public service.

Your website can then be associated with a public hostname without directly exposing your home's public IP address or opening inbound ports.

Cloudflare describes its Tunnel system as using an outbound-only connection, allowing a public hostname to be mapped to a local service such as a web server running on localhost.

That gives us another excellent computing discussion.

There are now at least two possible architectures:

Internet
   |
Router
   |
Port forwarding
   |
Raspberry Pi

or:

Internet
   |
Tunnel provider
   |
Encrypted outbound tunnel
   |
Raspberry Pi

Neither should simply be memorised.

Ask instead:

What are the advantages, disadvantages and security implications of each?

That is much closer to real computing.

What About HTTPS?

When browsing modern websites you will normally see:

https://

rather than:

http://

The S matters.

HTTPS encrypts the communication between the browser and web server and uses certificates to establish the site's identity.

This provides another natural extension to the project.

Instead of merely asking students to define encryption or digital certificates, let them investigate what has to happen to turn their own HTTP website into an HTTPS website.

Tools such as Certbot can obtain certificates and configure supported web servers, with automated renewal available on typical installations.

Now suddenly public-key cryptography, certificates and certificate authorities have a reason to exist.

A Website Is Only the Beginning

Once the basic server works, there are dozens of directions in which this project could develop.

You could create a personal portfolio.

You could host revision material.

You could build a household information page.

You could display data from a Raspberry Pi sensor.

You could connect a weather station.

You could create a database-backed application.

You could write a Python application and put a web interface in front of it.

You could make a dashboard displaying temperature, pressure, humidity or electricity generation.

You could create a small API that another computer queries.

You could even have several Raspberry Pis sending measurements back to one central server.

The simple HTML page has become the starting point for much more substantial computing projects.

My Favourite Extension — Build a Live Science Dashboard

For somebody interested in both computing and science, this is where things become especially interesting.

Imagine connecting a temperature sensor to the Raspberry Pi.

A Python program records:

Time
Temperature
Humidity
Pressure

The readings are saved.

The web server then displays them.

Now somebody on another computer can open a browser and see the latest measurement.

Add a graph and the project becomes better still.

You now have:

Sensor -> Raspberry Pi -> Python -> Data -> Web server -> Network -> Browser

That is a complete system.

Each individual element is understandable, but together they form something genuinely useful.

Turn It Into a Proper Student Investigation

Rather than providing every instruction, I would be tempted to give students a challenge:

Can you build a website on a Raspberry Pi that I can view from another computer without anybody telling you exactly how to do it?

Once they succeed, introduce the next challenge:

Can you work out how the second computer actually found the Raspberry Pi?

Then:

Can somebody outside our network see it?

Then:

Why not?

Then:

How could we make that possible safely?

That sequence transforms the exercise from following instructions into problem solving.

And that is where some of the best computing education happens.

Useful Questions to Ask Along the Way

A project like this can generate considerably more learning if students have to explain what is happening.

What does sudo actually do?

Why do we need apt update?

What is a Linux service?

Why does Apache continue running after we close the terminal?

Where are the website files stored?

Why can another computer access the Raspberry Pi?

What does an IP address identify?

Why does localhost work?

What is port 80?

What is the difference between a private and public IP address?

What does DNS do?

Why is HTTPS preferable to HTTP?

Why might directly exposing a home computer to the Internet be risky?

Those questions move the exercise far beyond simply copying commands.

From Command Line to Internet Server

This is exactly why I think students should experience Linux rather than merely learn definitions about it.

At the beginning we type:

sudo apt install apache2

It looks like just another Linux command.

But follow what happens next.

Software is downloaded.

A service starts.

A network port begins listening.

A second computer sends a request.

Linux receives it.

Apache processes it.

A file is retrieved from the filesystem.

It is transmitted across the network.

A browser interprets it.

A website appears.

Then perhaps we introduce DNS.

Then HTTPS.

Then server logs.

Then scripting.

Then databases.

Then security.

One small Raspberry Pi has become a laboratory for understanding an enormous proportion of modern computing.

Conclusion — Don't Just Learn Linux. Build Something With It.

There is a danger when teaching computing that operating systems, networks, programming and cybersecurity become separate chapters.

Students learn a definition of an IP address.

Then they learn some Linux commands.

Then perhaps some HTML.

Then they learn that port 80 is used for HTTP.

Then they memorise what DNS does.

A web-server project pulls those separate ideas back together.

The IP address now has a purpose because we need to find our Raspberry Pi.

HTML has a purpose because we need something for Apache to serve.

Ports matter because requests must reach the correct service.

DNS matters because people prefer names to numbers.

Linux permissions matter because server files must be controlled.

HTTPS matters because communication across a public network should be protected.

Cybersecurity matters because putting a computer on the Internet has consequences.

And perhaps most importantly, the student finishes with something that actually works.

There is a considerable difference between being told how a web server works and typing an address into a browser on another computer and seeing a page that is being delivered by a Raspberry Pi sitting on your own desk.

That is when Linux starts to feel less like another topic in Computer Science.

It starts to feel like a tool.

And once students realise that, there is an enormous amount they can build next.

11 September 2026

Making Glue from Milk — The Chemistry of Casein, Coagulation and Precipitation

Milk does not immediately suggest itself as a building material.

We pour it over cereal, add it to tea and coffee, turn it into yoghurt and cheese, and perhaps occasionally forget about it at the back of the fridge.

But hidden inside milk is a substance that can be separated, treated and turned into something quite unexpected:

glue.

The key ingredient is casein, the main family of proteins found in cow's milk.

By adding acid to milk, we can make those proteins come out of suspension as solid curds. Separate those curds, remove as much liquid as possible, and then treat the casein appropriately, and we can produce a surprisingly effective adhesive.

It is an excellent experiment because what initially looks like a simple kitchen activity opens the door to some serious chemistry.

We encounter:

proteins;
acids;
pH;
electrical charge on molecules;
colloids;
precipitation;
coagulation;
filtration;
neutralisation;
polymers;
intermolecular forces;
and the science of adhesives.

It also provides a wonderful reminder that chemistry is not simply about producing coloured solutions in test tubes.

Sometimes chemistry produces useful materials.

Milk Is Much More Complicated Than It Looks

At first glance, milk appears to be a simple white liquid.

Chemically, however, it is a remarkably complicated mixture containing:

water;
proteins;
fats;
lactose;
calcium compounds;
vitamins;
minerals;
and many other dissolved or suspended substances.

Approximately 80% of the protein in cow's milk is casein.

But casein is not simply floating around as individual protein molecules.

Much of it is organised into tiny structures called casein micelles.

These microscopic particles remain dispersed through the water in milk, contributing to its familiar white appearance.

Under normal conditions, the micelles repel one another sufficiently to remain dispersed.

Change the chemistry of their surroundings, however, and that stability can disappear.

That is exactly what we are going to do.

The Key Idea — Make the Casein Precipitate

One of the easiest ways of separating casein from milk is to make the milk more acidic.

Ordinary white vinegar works very well because it contains dilute ethanoic acid, also known as acetic acid.

Milk normally has a pH somewhere around 6.5 to 6.8.

Casein proteins contain groups that can gain or lose H+ ions depending upon the pH.

As the pH falls towards approximately 4.6, casein reaches what chemists call its isoelectric point.

This is extremely important.

At the isoelectric point, the overall electrical charge on the protein is approximately zero.

The protein particles therefore repel each other much less strongly.

Instead of remaining distributed through the liquid, they begin sticking together.

The casein coagulates and precipitates.

Suddenly our smooth white milk begins separating into:

solid curds and liquid whey.

Anyone who has made cheese will recognise what is happening.

Precipitation, Coagulation and Cheese Chemistry

This gives us an opportunity to introduce several useful scientific words.

Precipitation

A substance that was previously dispersed or dissolved comes out of the liquid as a solid.

Coagulation

Small particles come together to form larger clumps or masses.

In this experiment the casein particles lose much of the electrostatic repulsion that normally keeps them apart.

They aggregate.

We see this as curds forming in the milk.

The remaining liquid is often called whey.

This is very similar to some of the chemistry used in food production.

But our objective is not cheese.

We are going to turn our casein into an adhesive.

What You Will Need

For a straightforward investigation you need:

about 100 mL of skimmed or semi-skimmed milk;
approximately 10-15 mL of white vinegar;
a small saucepan, beaker or heat-resistant container;
a thermometer if available;
a spoon or stirring rod;
filter paper, muslin, cheesecloth or a fine kitchen sieve;
paper towel;
sodium bicarbonate;
a small container for making the glue;
two wooden lolly sticks or pieces of wood for testing it.

Skimmed milk is particularly useful because the lower fat content generally gives a cleaner casein preparation.

Whole milk will still work, but the additional fat can make the separated material feel greasier.

Stage One — Warm the Milk

Measure approximately 100 mL of milk.

Warm it gently to around 40-50 degrees C.

It does not need to boil.

In fact, vigorous boiling is unnecessary and can complicate the experiment.

The warming simply helps the acid interact with the milk and allows the casein to coagulate relatively quickly.

Already there is a useful scientific point here.

Students often assume that whenever heat is used in an experiment, heat must be causing the chemical change.

Here it is mainly helping the process occur efficiently.

The acid is the crucial ingredient.

Stage Two — Add the Vinegar

Add approximately 10 mL of white vinegar while stirring gently.

The transformation can be remarkably rapid.

Within moments the previously smooth milk begins looking lumpy.

White solids appear.

The liquid surrounding them becomes more transparent and slightly yellowish.

Those solids contain the precipitated casein.

Add a little more vinegar if necessary until separation appears reasonably complete.

It is worth stopping at this stage and simply looking.

This is one of those practical experiments where the change is visually obvious enough that very little explanation is initially required.

Something fundamental has happened to the milk.

What Has the Acid Actually Done?

A very simplified explanation would be:

acid makes the casein precipitate.

But the underlying chemistry is more interesting.

Casein molecules contain acidic and basic groups.

The electrical charge carried by the proteins therefore depends upon the surrounding pH.

At normal milk pH, casein micelles carry sufficient charge to help keep them dispersed.

Adding ethanoic acid increases the concentration of H+ ions.

As the pH approaches the isoelectric point of casein, the overall charge decreases.

Repulsion between neighbouring protein particles becomes weaker.

They begin aggregating.

At the same time, acidification affects the calcium phosphate associated with the casein micelles, further destabilising their structure.

The result is the spectacular coagulation that we can actually see.

Is This Just Protein Denaturation?

Students may immediately think of cooking an egg.

Heating egg white causes proteins to unfold and form a solid network.

That is commonly described as protein denaturation.

Casein precipitation is slightly different.

Caseins do not have the same tightly folded structures as many other proteins.

Here, reducing the electrical charge and destabilising the casein micelles is especially important.

So although the words coagulation and denaturation are sometimes used rather loosely in everyday explanations, the chemistry deserves a little more care.

What we are primarily observing is acid-induced casein precipitation and aggregation.

Stage Three — Separate the Casein

Pour the mixture through filter paper, muslin or a fine sieve.

The liquid whey passes through.

The solid casein remains behind.

Press the casein gently with paper towel to remove as much liquid as possible.

You can rinse the curds with a little clean water and filter them again if you want to remove some of the remaining acid and soluble material.

Eventually you should have something resembling a soft white paste or crumbly putty.

At this stage it still does not look particularly promising as glue.

But we have now separated a natural polymer from milk.

Stage Four — Turn the Casein into Glue

Transfer the casein to a small container.

Add a small amount of sodium bicarbonate.

Start with perhaps a quarter of a teaspoon for casein obtained from around 100 mL of milk.

Mix thoroughly.

You may notice some gentle fizzing.

This occurs because sodium bicarbonate reacts with remaining acid.

A simplified ionic equation is:

H+ + HCO3- -> CO2 + H2O

The carbon dioxide produces the bubbles.

The bicarbonate also raises the pH.

This helps transform our acidic casein curds into a smoother and more usable adhesive paste.

Add a few drops of water if necessary.

The objective is not to produce a thin liquid.

You want something resembling a thick glue.

Why Should Protein Work as Glue?

This is perhaps the most interesting question in the entire experiment.

Why should something extracted from milk stick pieces of wood together?

Proteins are enormous molecules.

Casein molecules contain many different chemical groups capable of interacting with other substances.

When casein glue is spread across a surface, it can make close contact with microscopic irregularities in the material.

At the molecular level there can be interactions including:

hydrogen bonding;
electrostatic interactions;
attraction between polar groups;
and mechanical interlocking with pores and rough surfaces.

As water leaves the adhesive during drying, the casein molecules become increasingly concentrated.

Eventually they form a solid protein-rich layer between the two surfaces.

We have effectively created a natural polymer adhesive.

Test the Glue

A scientific investigation should not finish with:

"It looks like glue."

We should test whether it actually works.

Take two wooden lolly sticks.

Overlap them by perhaps 2 cm.

Spread approximately the same amount of casein glue over the overlapping region.

Clamp them together or place a small weight on top while the adhesive dries.

Leave them for several hours, preferably overnight.

Then try pulling them apart.

The result can be surprisingly convincing.

Turn It into a Proper Investigation

This experiment becomes much more interesting when students begin changing variables.

For example:

Does milk type matter?

Compare:

skimmed milk;
semi-skimmed milk;
whole milk.

Keep everything else constant.

Which produces the most casein?

Which produces the strongest glue?

How Much Casein Can You Obtain?

You can also turn the practical into a quantitative experiment.

Weigh a clean dry filter paper before filtration.

Collect the casein and allow it to dry thoroughly.

Weigh everything again.

Calculate:

Mass of casein = final mass - mass of filter paper

You could then calculate percentage yield relative to the mass of milk used:

Percentage yield = mass of dry casein / mass of milk x 100

Students should be careful with their interpretation.

Milk contains plenty of water, so we are not expecting an enormous percentage yield.

Does the Amount of Acid Matter?

Try adding different quantities of vinegar to identical volumes of milk.

For example:

2 mL;
5 mL;
10 mL;
15 mL;
20 mL.

Measure the mass of casein obtained.

At first, increasing the acid concentration should promote more complete precipitation.

Eventually, however, adding more acid should produce little additional benefit.

This is a useful demonstration of an important experimental principle:

more reagent does not necessarily mean more product indefinitely.

Measure the pH

If you have a pH meter or suitable pH probe, the experiment becomes considerably more informative.

Measure the starting pH of the milk.

Then add vinegar gradually while monitoring the pH.

Watch carefully as coagulation becomes extensive near the casein isoelectric region.

This converts what looks like an elementary kitchen experiment into a very good piece of analytical chemistry.

You can plot:

mass of casein precipitated against pH

or perhaps:

turbidity against pH

if suitable sensors are available.

Which Acid Works Best?

Another extension would be to compare different food-safe acids.

You might investigate:

white vinegar;
lemon juice;
citric acid solution.

Use solutions of comparable acidity where possible.

Students could investigate whether the type of acid matters or whether the principal factor is simply the pH achieved.

This is where experimental design becomes important.

If one sample receives much more acid than another, we cannot confidently say that differences arose because the acids themselves were different.

How Strong Is Our Milk Glue?

The most enjoyable extension may be engineering rather than chemistry.

Prepare several identical wooden joints.

Glue each pair using a different adhesive.

For example:

casein glue;
PVA glue;
flour paste;
starch adhesive.

Allow each sample to dry for the same length of time.

Then gradually add mass until the joint fails.

A simple results table might contain:

Adhesive	Overlap area	Drying time	Maximum load before failure
Casein	4 cm2	24 h	...
PVA	4 cm2	24 h	...
Flour paste	4 cm2	24 h	...

Now students are not simply making glue.

They are carrying out materials testing.

Be Careful About What You Call "Strong"

Suppose one glue supports a heavier mass than another.

Is that enough to declare it better?

Perhaps not.

We might also ask:

How long did it take to dry?
Was the joint waterproof?
Did the glue remain flexible?
Did it become brittle?
How easily could it be applied?
How long could it be stored?
Did it stick better to wood than plastic?
What happened in humid conditions?

Real engineering decisions rarely depend upon a single measurement.

The "best" material depends upon what we want the material to do.

A Glue with a Long History

Casein adhesives are not simply a classroom curiosity.

Before modern synthetic glues became widespread, casein-based adhesives were important materials for woodworking and plywood manufacture.

They offered a way of creating useful adhesives from naturally occurring proteins.

Modern synthetic adhesives such as PVA, epoxies and polyurethane products have largely replaced casein glue for many applications because they can offer better consistency, durability and water resistance.

Nevertheless, making casein glue gives students a glimpse of an earlier form of materials technology.

It also challenges an assumption we make increasingly often:

that useful manufactured materials must begin with petroleum or sophisticated industrial chemicals.

Nature already produces extraordinarily complicated polymers.

Sometimes chemistry is about learning how to separate and use them.

Milk, Cheese and Glue Are Connected by Chemistry

One of my favourite features of this experiment is the way it links apparently unrelated objects.

Milk.

Cheese.

Protein.

Glue.

They appear to belong to completely different worlds.

But at molecular level the connections become obvious.

Cheese making relies upon manipulating milk proteins.

Our glue-making experiment does something related, but instead of preparing food we deliberately recover the protein as a functional material.

This is one of the strengths of practical science.

The divisions between "food science", "chemistry" and "materials science" start disappearing.

There is simply matter — and what happens when we alter its conditions.

A Good Experiment for Discussing Colloids

Milk also gives us an opportunity to discuss something that receives surprisingly little attention in school science:

colloids.

Not every mixture is simply a solution or a suspension.

Milk contains extremely small particles dispersed through another substance.

Its proteins and fats interact with water in complicated ways.

Colloids are everywhere.

Examples include:

milk;
mayonnaise;
fog;
smoke;
paint;
shaving foam;
gelatin;
many cosmetics;
and numerous medicines.

Changing the conditions surrounding a colloid can cause it to become unstable.

Our precipitating casein is a beautiful example.

Common Problems

Nothing seems to happen

The milk may not be sufficiently warm, or you may not have added enough acid.

Add vinegar gradually while stirring.

The mixture is very greasy

You may be using milk with a high fat content.

Try skimmed milk.

The casein glue is too runny

Too much water has probably been added.

Add water only a few drops at a time.

The glue is too crumbly

Mix the casein more thoroughly with a small quantity of sodium bicarbonate and a few drops of water.

The joint seems weak

Allow considerably longer for drying.

Casein adhesive needs water to evaporate before maximum strength develops.

Also check that your surfaces are clean and make reasonably close contact.

Safety

Although this is a comparatively low-risk practical, normal laboratory precautions still apply.

Do not eat or drink laboratory materials.
Milk proteins can cause allergic reactions in people with milk allergies.
Take care when heating liquids.
Do not boil the milk unnecessarily.
Wash hands after the experiment.
Clean surfaces and equipment afterwards.
Once milk has been used experimentally, treat it as laboratory material rather than food.
Do not store homemade casein glue for long periods. Make a fresh batch when required.

Young students should carry out heating and chemical handling with appropriate adult supervision.

What Students Are Really Learning

At first sight, this might appear to be a novelty experiment.

"Make glue from milk."

But scientifically it contains far more depth than that description suggests.

Students encounter:

Biology:
Proteins and their properties.

Chemistry:
Acids, pH, neutralisation, precipitation and molecular charge.

Physics:
Intermolecular forces and material behaviour.

Materials science:
Polymers, adhesives and mechanical testing.

Experimental science:
Variables, controls, measurement, repeatability and data interpretation.

That combination makes it particularly valuable.

A good practical does not merely illustrate something students already know.

It gives them something new to think about.

From Breakfast to Materials Science

Perhaps the most memorable moment comes at the very beginning.

You start with an ordinary glass of milk.

Add a little acid.

Suddenly the liquid separates.

Filter it.

Treat the solid.

Spread it between two pieces of wood.

The following day those pieces may be firmly attached.

Nothing magical has occurred.

We have simply changed the conditions surrounding a naturally occurring polymer.

But that is precisely why the experiment is so satisfying.

Science allows us to look at an everyday substance and ask a completely different question.

Not:

"Can I drink this?"

but:

"What is actually inside it, how can I separate those substances, and what else could they do?"

That change of perspective is at the heart of good science.

Milk is not merely milk.

It is water, sugars, minerals, fats and proteins assembled into an extraordinarily complicated material.

And hidden among those proteins is casein — waiting for a little chemistry to turn breakfast into glue.

10 September 2026

There Are Barcodes Hidden in Starlight

Look up at a star on a clear night and, to the naked eye, it does not seem to give us very much information.

It is a point of light.

Perhaps it looks slightly blue, yellow or orange. Perhaps it is brighter than another star nearby. But that seems to be about it.

And yet astronomers can use that tiny quantity of light to work out an extraordinary amount about an object that may be hundreds, thousands or even millions of light-years away.

They can determine what elements it contains.

They can estimate its temperature.

They can measure whether it is moving towards us or away from us.

They can sometimes determine how rapidly it is rotating.

They can investigate the gases in the atmosphere of a distant planet.

And in some circumstances they can even infer the presence and strength of magnetic fields.

All of this begins with one deceptively simple idea:

Split the light apart and look carefully at the colours.

That is spectroscopy.

And it is one of the finest examples in science of how careful measurement can reveal information that appears, at first, to be completely inaccessible.

Light Contains More Information Than Our Eyes Can See

When we look at ordinary white light, our eyes simply interpret it as white.

Pass that light through a prism or diffraction grating, however, and something remarkable happens.

The light separates into its component wavelengths.

We see a spectrum.

The familiar visible spectrum runs approximately from:

violet;
blue;
green;
yellow;
orange;
red.

But the spectrum is not always a smooth rainbow.

Sometimes it contains bright coloured lines.

Sometimes it contains dark gaps.

Sometimes certain wavelengths are much stronger than others.

Those details form a kind of scientific fingerprint.

Or, perhaps more accurately for modern students, a barcode.

The pattern tells us something about the atoms, molecules and physical conditions that produced the light.

That is why spectroscopy is such a powerful idea to introduce beyond the normal school syllabus.

Students are not simply observing colour.

They are learning that light carries encoded information about matter.

Start Somewhere Much Closer Than the Stars

One of the best ways to introduce astronomical spectroscopy is not to begin with astronomy at all.

Begin in the laboratory.

Look at ordinary light sources.

Even quite simple equipment can produce surprisingly interesting results.

A diffraction grating, handheld spectroscope or suitably arranged spectrometer can be used to examine:

an incandescent lamp;
an LED lamp;
a fluorescent tube;
a sodium lamp;
daylight;
different coloured LEDs;
computer and television screens.

Students very quickly discover that "white light" is not always produced in the same way.

And that is where the experiment becomes interesting.

An Incandescent Lamp — A Continuous Spectrum

An old-style incandescent lamp works by heating a filament until it becomes extremely hot.

Look at its light through a spectroscope and you see something reasonably close to a continuous rainbow.

There is light across a wide range of visible wavelengths.

This is very different from what we see from many modern sources.

It also gives us a useful introduction to the idea of thermal radiation.

A hot object emits a range of wavelengths.

As its temperature increases, the distribution of those wavelengths changes.

We can see this in everyday life.

A piece of metal being heated may first glow dull red.

At a higher temperature it becomes orange.

Eventually it may appear yellow-white.

Temperature is changing the spectrum.

Stars behave in a related way.

Their colour therefore tells astronomers something about their surface temperature.

A red star is not simply "painted red".

Its colour is connected with its physical temperature.

LEDs — Not All White Light Is the Same

Modern LED lamps provide a particularly good surprise.

Students may expect a white LED bulb to produce the same smooth rainbow as an incandescent lamp.

Often it does not.

Many white LEDs are made using a blue LED together with phosphor materials that convert some of the blue light into longer wavelengths.

Depending upon the lamp, the resulting spectrum may show a strong blue peak combined with a broader region at other wavelengths.

Different LED lamps can produce noticeably different spectra even though they all look white to the human eye.

This immediately gives students an important lesson.

Objects that appear identical to our senses may be physically very different when measured scientifically.

Our eyes integrate many wavelengths together.

A spectroscope separates them again.

Fluorescent Lamps — A Forest of Lines

Fluorescent lighting gives another very different spectrum.

Instead of a smooth rainbow, students are likely to see several particularly bright lines or bands.

These arise from the gases and phosphors involved in producing the light.

Suddenly spectroscopy begins to look much more like a barcode.

There are particular wavelengths present much more strongly than others.

Those wavelengths can act as clues to the substances involved.

This leads naturally towards atomic emission spectra.

Sodium — A Beautiful Demonstration

If a suitable sodium source is available, it provides one of the classic spectroscopy demonstrations.

Sodium produces extremely characteristic yellow emission close to 589 nm.

With sufficient resolution, the familiar yellow region can be resolved into the famous sodium D lines.

The important point for students is not necessarily the precise wavelength.

It is the principle.

Sodium atoms do not emit every possible colour equally.

They produce very specific wavelengths.

Those wavelengths are connected with changes in the energy states of electrons within the atom.

Each element has its own characteristic pattern.

Hydrogen has one pattern.

Helium has another.

Neon has another.

Sodium has another.

That makes spectroscopy a method of chemical identification.

Why Do Atoms Produce Particular Colours?

This is where the experiment begins to connect with atomic physics.

Electrons in atoms are not allowed to possess just any energy.

They occupy particular energy levels.

If an electron moves from a higher energy state to a lower one, energy can be released as a photon.

The energy of that photon is related to its frequency by:

E = hf

where:

E = photon energy
h = Planck's constant
f = frequency

Because only certain energy differences are permitted within the atom, only particular photon energies are produced.

That means only particular frequencies — and therefore particular wavelengths — appear in the spectrum.

The result is a set of spectral lines.

The positions of those lines are characteristic of the element producing them.

It is rather like giving every element its own optical signature.

Emission Lines and Absorption Lines

There are two particularly important types of spectrum to introduce.

Emission spectra

A hot, low-density gas can produce bright lines at specific wavelengths.

Those bright lines show the wavelengths emitted by atoms or molecules in the gas.

Absorption spectra

If continuous light passes through a cooler gas, particular wavelengths may be absorbed.

The spectrum then contains dark lines.

The remarkable thing is that the positions of those dark absorption lines correspond to wavelengths that the same substance can emit.

This becomes enormously important in astronomy.

We cannot travel to a star, scoop up a sample of its atmosphere and bring it back to the laboratory.

But light from deeper, hotter regions of a star passes through cooler material in the star's atmosphere.

Atoms in that atmosphere absorb particular wavelengths.

The resulting dark absorption lines tell us what substances are present.

We read the lines.

The lines tell us the chemistry.

How Do We Know What Stars Are Made Of?

This is perhaps the most extraordinary part of spectroscopy.

Suppose we observe a dark line at a particular wavelength in the spectrum of a star.

How do we know what caused it?

We compare it with laboratory measurements.

Scientists can excite samples of hydrogen, helium, sodium, calcium, iron and many other substances here on Earth.

They measure the wavelengths at which those substances absorb or emit light.

Then they compare those laboratory patterns with spectra from stars.

If the lines match, we have evidence that the same element is present.

This is one of those moments in science that deserves to be appreciated.

The laws of physics appear to work in the same way in a laboratory on Earth and in stars vast distances away.

The sodium atom in a lamp in a laboratory behaves according to the same physics as a sodium atom in the atmosphere of a distant star.

That is a profound idea.

A Wonderful Historical Twist — Helium Was Found in the Sun First

Spectroscopy also produced one of the loveliest stories in the history of science.

During observations of the Sun in the nineteenth century, astronomers noticed a spectral line that did not correspond to any element then known on Earth.

The line was associated with a previously unknown element.

It was named helium after Helios, the Greek Sun god.

Only later was helium identified on Earth.

In other words, an element was detected in the Sun before it was found terrestrially.

A substance nearly 150 million kilometres away was identified using nothing more than the light arriving from it.

That should give students some sense of just how powerful spectroscopy can be.

Temperature Is Written into the Spectrum Too

Spectroscopy does more than reveal composition.

The overall shape of the spectrum contains information about temperature.

Hot objects produce thermal radiation across a range of wavelengths.

As temperature increases, the wavelength at which the radiation is most intense shifts.

Qualitatively:

cooler stars tend to appear redder;
hotter stars tend to appear bluer.

This sometimes surprises students because everyday experience teaches us to associate red with hot and blue with cold.

In astronomy, the opposite applies to stellar colour.

Blue stars are generally hotter than red stars.

For example, the surface temperature of a cool red star may be only a few thousand kelvin, while a hot blue star may exceed 10,000 K.

That is another reason why colour in astronomy is not merely aesthetic.

It is data.

Stars Can Tell Us Whether They Are Moving

Spectroscopy becomes even more impressive when we consider motion.

Suppose we know where a particular hydrogen absorption line should appear.

If the star is moving towards us, its spectral lines may appear shifted slightly towards shorter wavelengths.

This is a blueshift.

If the star is moving away, the lines shift towards longer wavelengths.

This is a redshift.

For relatively low speeds, the relationship can be approximated by:

v / c = change in wavelength / original wavelength

or:

v / c = Δλ / λ

where:

v = radial velocity of the object
c = speed of light
Δλ = change in wavelength
λ = original wavelength

This means astronomers can measure motion along our line of sight without seeing the star physically move across the sky.

Again, the information is hidden inside the light.

Finding Planets Without Seeing Them

This provides a lovely connection with another astronomical topic: exoplanets.

A planet orbiting a star does not simply travel around a perfectly stationary object.

The star and planet actually orbit their common centre of mass.

As a result, the star moves slightly backwards and forwards.

That movement can cause its spectral lines to alternate between tiny redshifts and blueshifts.

This is the radial velocity method of exoplanet detection.

We may never directly see the planet.

Instead we detect the extremely small gravitational effect it has upon its star.

This is a wonderful example of indirect scientific reasoning.

We observe one thing.

We infer another.

Can Spectroscopy Tell Us How Fast a Star Rotates?

It can.

Imagine one side of a rotating star moving towards us while the opposite side is moving away.

Light from one side is slightly blueshifted.

Light from the other side is slightly redshifted.

The combined effect can broaden the spectral lines.

By studying that broadening, astronomers can estimate how rapidly the star is rotating.

This is a much more advanced application, but it is an excellent example to mention because it demonstrates how much information is contained within the precise shape of a spectral line.

Not merely whether a line exists.

Not merely where it is.

But even how wide it is.

Magnetic Fields Can Leave Their Mark as Well

Strong magnetic fields can alter atomic energy levels.

This can cause spectral lines to split into multiple components.

The effect is known as the Zeeman effect.

Astronomers can use this splitting to investigate magnetic fields in stars and other astronomical objects.

At this point spectroscopy has moved far beyond simply identifying chemicals.

The spectrum has become a diagnostic tool for the physical environment.

Composition.

Temperature.

Velocity.

Rotation.

Magnetism.

All encoded in light.

Reading the Atmosphere of Another World

One of the most exciting modern applications of spectroscopy involves exoplanet atmospheres.

Imagine a planet passing in front of its star.

Most of the starlight travels directly towards us.

But a small fraction passes through the planet's atmosphere before reaching our telescopes.

Atoms and molecules in that atmosphere absorb particular wavelengths.

By comparing the spectrum during the transit with the normal stellar spectrum, astronomers can sometimes identify substances in the planetary atmosphere.

Depending upon the planet and the quality of the observations, spectroscopy can reveal signatures associated with substances such as:

water vapour;
sodium;
carbon dioxide;
methane;
other atmospheric gases.

This does not mean that every molecule automatically indicates life.

That is an important scientific caution.

Atmospheric chemistry is complicated, and biological and non-biological processes can sometimes produce similar substances.

But spectroscopy gives us something that would have seemed astonishing only a few generations ago:

the ability to study the atmosphere of a planet orbiting another star.

A Practical Spectroscopy Investigation

This topic lends itself beautifully to a home laboratory, school laboratory or astronomy club.

You do not need a professional observatory to introduce the underlying science.

Equipment

Depending upon what is available, you might use:

a handheld spectroscope;
a diffraction grating;
a simple educational spectrometer;
a camera with a diffraction grating;
suitable spectrum-analysis software;
several different lamps or light sources.

Suitable sources might include:

incandescent filament bulbs;
LED lamps;
coloured LEDs;
fluorescent lamps;
sodium lamps where safely available;
computer displays;
phone or tablet displays;
daylight.

Investigation 1 — Are All White Lights Actually the Same?

Place several apparently white light sources side by side.

For example:

an incandescent lamp;
a warm-white LED;
a cool-white LED;
a fluorescent source.

Look at each through the spectroscope.

Ask students to describe the differences.

They might consider:

Is the spectrum continuous?
Are particular colours stronger?
Are there obvious bright lines?
Are there gaps?
How do two different white LEDs compare?

This is a wonderfully simple experiment because the student's eyes initially say:

"They are all white."

The spectroscope says:

"No, they are not."

That is science in miniature.

Measurement reveals structure that ordinary observation misses.

Investigation 2 — Compare Coloured LEDs

Use red, green and blue LEDs.

Observe their spectra.

A red LED does not simply contain "white light with the other colours removed".

Its output is concentrated into a relatively narrow region of wavelengths.

Students can compare different LED colours and consider why a nominally single-colour light source still has a finite spectral width.

More advanced students could investigate the relationship between LED colour and photon energy.

Because:

E = hf

and:

c = fλ

we can combine them to obtain:

E = hc / λ

Shorter wavelength photons therefore have more energy than longer wavelength photons.

Blue LED photons have more energy than red LED photons.

That provides a useful bridge between visible colour, wave physics and quantum physics.

Investigation 3 — Look at a Computer Screen

This is particularly effective because it connects spectroscopy with something students use every day.

Display a white image on a computer monitor, tablet or television and examine it through a spectroscope.

Depending upon the display technology, students may be able to see separate red, green and blue contributions.

Then display:

red;
green;
blue;
yellow;
cyan;
magenta;
white.

Ask what changes in the spectrum.

Students begin to see that the screen is creating perceived colour by controlling a small number of primary emitters.

White on a display is constructed.

It is not necessarily the same spectrum as white daylight.

Investigation 4 — Match an Unknown Spectrum

This turns the activity into a genuine scientific puzzle.

Provide spectra from several known sources.

Then present an unknown.

Students must identify it by comparing the pattern.

This mimics the basic reasoning astronomers use when identifying chemical elements.

The task can be made increasingly sophisticated.

At first students may simply match obvious patterns visually.

Later they could measure approximate wavelengths.

They could produce a table such as:

Observed wavelength	Possible element
486 nm	Hydrogen
589 nm	Sodium
656 nm	Hydrogen

The exact activity will depend upon the resolution of the equipment, but the principle is powerful.

Students are no longer merely observing.

They are interpreting evidence.

Investigation 5 — From Laboratory Spectrum to Stellar Spectrum

This is probably the strongest extension.

Give students a published spectrum of a star.

Provide laboratory reference spectra for several elements.

Ask:

Which elements appear to be present?

Students can look for matching patterns.

One matching line is usually weak evidence.

Several matching lines provide a much stronger case.

That becomes a useful lesson in scientific reasoning.

Scientists do not normally identify a substance because one feature happens to look similar.

They search for a consistent pattern of evidence.

A Further Challenge — Can We Build a Simple Spectrometer?

For students who enjoy engineering as well as astronomy, a homemade spectrometer is an excellent project.

A simple design can use:

a narrow entrance slit;
a diffraction grating;
a dark enclosure;
a camera.

The slit restricts the incoming light.

The diffraction grating separates it by wavelength.

The camera records the spectrum.

With suitable calibration, pixel position across the photograph can be related to wavelength.

Calibration might use a known spectral line from a particular source.

Students then move from merely looking at spectra to actually measuring them.

That is a significant conceptual step.

What Does a Diffraction Grating Actually Do?

A diffraction grating contains a very large number of closely spaced lines.

Light passing through or reflecting from the grating interferes.

Different wavelengths emerge strongly at different angles.

A simplified diffraction-grating relationship is:

nλ = d sin θ

where:

n = diffraction order
λ = wavelength
d = spacing between grating lines
θ = diffraction angle

Students who have studied waves may recognise this as another application of interference.

Spectroscopy therefore connects astronomy with wave physics.

The grating does not somehow "colour" the light.

It separates wavelengths that were already present.

What About Looking at the Sun?

The Sun is obviously an exceptionally interesting source for spectroscopy.

Its spectrum contains thousands of absorption lines.

Historically these dark lines are strongly associated with the work of Joseph von Fraunhofer and are often called Fraunhofer lines.

But this also introduces an essential safety issue.

Never look directly at the Sun through optical equipment

Students should never aim:

a telescope;
binoculars;
magnifying lenses;
cameras with optical viewfinders;
homemade optical systems

directly at the Sun unless the equipment is specifically designed and correctly filtered for solar observation.

Concentrated sunlight can cause permanent eye damage extremely rapidly.

For simple educational spectroscopy, use safely projected sunlight or diffuse daylight rather than direct solar viewing.

This is a topic where the science is fascinating, but correct optical safety must come first.

Why I Like This Experiment So Much

There are some experiments that demonstrate a fact.

And then there are experiments that change how a student thinks about what it means to observe something.

Spectroscopy belongs firmly in the second category.

A student looks at an LED and sees white light.

Then they look through a spectroscope and discover structure.

They look at a fluorescent lamp and discover lines.

They look at a sodium source and discover a characteristic signature.

Then you show them a stellar spectrum.

And suddenly the leap becomes possible.

The same physics applies.

The laboratory is no longer disconnected from astronomy.

The student has effectively learned one of the tools used to investigate the Universe.

That is what I particularly like about practical science.

You can begin with an ordinary lamp sitting on a laboratory bench and finish by discussing what distant stars and planets are made of.

The Bigger Lesson — Science Often Means Learning How to Ask Nature Better Questions

The human eye is an extraordinary instrument, but it has limits.

Looking harder at a star does not tell us very much more.

Building a better question does.

Instead of asking:

"What colour is the star?"

we ask:

"Exactly which wavelengths of light are present?"

Instead of asking:

"Does this star appear to move?"

we ask:

"Have its spectral lines shifted?"

Instead of asking:

"What is its atmosphere made of?"

we ask:

"Which wavelengths have been absorbed?"

This is one of the deeper lessons of science.

Progress often comes not from observing the same thing more intensely, but from inventing a new way to measure it.

A spectroscope gives us a different way of looking.

And once we look in that way, the apparently featureless point of light becomes an extraordinary source of information.

Conclusion — Every Star Is Sending Us a Message

Stars are impossibly distant by everyday standards.

We cannot touch them.

We cannot collect samples from most of them.

We cannot place thermometers in their atmospheres.

We cannot follow them with speed cameras.

Yet they continually send something across space towards us.

Light.

And hidden within that light is information.

Chemical composition.

Temperature.

Motion.

Rotation.

Magnetic fields.

Atmospheric chemistry.

Perhaps even clues about planets orbiting stars that our ancestors did not know existed.

All we have to do is learn how to read it.

A spectrum is therefore much more than a rainbow.

It is a message.

And spread across that message are the barcodes of the Universe.

Questions to Explore

For students who want to take the idea further:

Why does a hot solid produce a different spectrum from a hot low-density gas?
Why do absorption and emission lines for the same element occur at the same wavelengths?
Why are blue stars hotter than red stars?
How can spectral lines reveal the speed of a star?
How can line broadening reveal stellar rotation?
Why might several spectral lines be needed before confidently identifying an element?
How can an exoplanet atmosphere affect the spectrum of its parent star during a transit?
Why would finding oxygen in an exoplanet atmosphere not automatically prove that life exists?
How could you calibrate a homemade spectrometer?
What other parts of the electromagnetic spectrum can astronomers use besides visible light?