Fun with crystals

If you look closely at sugar or salt, you will see it is made up of lots of little crystals. We can ‘grow’ bigger crystals if we start from scratch and let them form slowly. So how do we make a crystal from scratch? We need to dissolve the salt or sugar and then let it recrystalise. You can try out these two experiments to make some rock candy and geodes. Both of these involve boiling water so definitely one for some grown-up help.

Rock candy

Heat a cupful of water in a pan until it is boiling. Then start adding sugar. Stir, add more sugar, stir, add more sugar, stir…you get the idea! Keep going until you cannot get any more to dissolve, this should be at least two cupfuls. This is called a saturated solution. Let the mixture cool down for around 20 minutes then pour into a tall glass. When the solution cools we say it supersaturated, this means it now has more sugar than it can normally hold. It’s ready to start growing crystals! If you hang a bamboo skewer into the glass (use a clothes-peg to keep it in place), crystals of sugar will start to form on the skewer. Remember we need SLOW formation so it will take a few days, perhaps even a week, be patient! It’s really important that it is left undisturbed for this time so put it somewhere out of the way.


Geodes are mineral crystals found inside rocks, we can make our own inside eggshells. Make sure the eggshells are perfectly clean and the membrane has come away from the inside. Make a saturated solution like you did before, you can use sugar or try table salt or Epsom salts, then add a little food colouring. Pop the shells in an egg box and fill with this solution, the fuller the better but make sure they won’t spill! Leave them somewhere safe to evaporate and in a few days you should see the geodes form!

Crystals in nature

Crystals form in nature when some things become solids. This can be rocks that were molten (lava) or minerals that were dissolved in water. Molten rocks will solidify as they cool, dissolved mineral will crystalise as the water evaporates.

The size of the crystals depends on the time that they take to form. Fast=small, slow=big. Igneous rocks (ones that are made from lava or magma) might have small crystals if they came from a volcano as they would cool quickly in the air. Sometimes igneous rocks can be made slowly underground and we can often see larger crystals in these. Geodes come from dissolved minerals seeping into gaps in other rocks, the water evaporates soooo slowly that we get beautiful big crystals. You can try putting your egg geodes in different places when they are evaporating, perhaps one on a radiator, one on a windowsill and one somewhere cold. Just make sure they’re not going to get knocked over!



It’s time to get messy! Here is one you definitely don’t want to do in your kitchen, take the experimenting outdoors.

You may have already seen or heard about the Coke and Mentos experiment. Basically you drop some Mentos in a bottle of Diet Coke and stand well back as it makes a big fizzy mess! First, you need to know what is going on. Fizzy drinks are just flavoured drinks that have a whole load of carbon dioxide gas dissolved into them. The gas stays trapped inside for as long as the lid is screwed on tight, when you take the lid off it will slowly come out as small bubbles. This is what makes the drink ‘fizzy’. If you’re a very patient person who really likes watching bubbles, you could sit and watch it for a couple of days while each bubble gradually makes its way out. I’m guessing that you would like something a bit more dramatic! By dropping things into the bottle, you can get all those bubbles to form at once and rush out of the bottle in a big fountain. The most famous example is the Mento but it is not the only contender for best fizz-producer. You can try out other sweets, salt, sugar, cake sprinkles…whatever you have in the cupboard. Try different drink brands and flavours, which is best? All of them work by the rough surface of the sweet providing ‘nucleation sites’, these are places where bubbles can easily form. Give them lots of nucleation sites and get lots of bubbles…simple!

You can see a slo-mo video of one of our explosions on our Facebook page. We’d love to see your exploding fizzy drinks so do share your videos with us on Instagram, Facebook or Twitter!

Two very important things that you need to know: (1) This is an OUTDOOR experiment!!! It makes a big mess so make sure it is on the grass or somewhere that spillage doesn’t matter. (2) Only use sugar-free drinks, they simply work better (and don’t leave a horrid sticky mess that will attract every ant in the world to your garden). You might like to make a cardboard tube ‘launcher’ so you can drop several sweets in at once. Be warned it ‘erupts’ pretty quickly so stand back!

And … do this outdoors (did I mention that?).

There are lots more experiments to try on our Home Science page. If you’d like a visit from a Fab Scientist to bring even more cool stuff to your birthday party or school, give us a shout!

Click here for more experiments


When you hear someone speak, you don’t just hear what they are saying. You can also tell where they are. Trick your ears by making this simple ‘Ear Switcher’. All you need is about a metre of hosepipe, a couple of funnels and some sticky tape. Cut the hose into two pieces, stick a funnel in the end of each one, then tape it together as in the picture. If you have a plastic Alice band, stick the whole thing on that to make it easier. Pop it on your head and hold the free ends of the tube in your ears (never stick anything right into your ear!). Now close your eyes and get someone to make noises, can you work out where they are? We normally work out direction because sounds reach one ear before the other. Sound travels super-fast (over 700 miles per hour) so there is only about a two-thousandth of a second between hearing it in one ear and then the other. Your brain is clever enough to notice that difference and use it work out a direction….until you confuse it with an Ear Switcher!


Volcanoes hold great fascination among children (and grown-ups!). Here are some ideas for making your own and experimenting with the best eruptions.

First you need to find out about volcanoes. Do you have any books about them? Try looking up ‘volcano facts for kids’ on the internet. There are some great pictures and videos available too. Do you want to make a cinder cone, stratovolcano or shield volcano? Then think about what to make it out of. You could use sand, salt dough, paper mache, Lego, junk…be creative. It will get messy though! Whatever you make it out of, it needs to be on a big tray to catch the ‘lava’. Put a small bottle inside to be the ‘magma chamber’, make sure you don’t cover the top of this.

Experimenting with eruptions 

There are a few options for making your volcano erupt. You can try them out (on a tray or in the sink!) before choosing one to go in your volcano model.

The most common is vinegar and bicarbonate of soda. Just mix a tablespoon or two of bicarbonate of soda with about a cupful of warm water. Pour it into a small bottle, add a squirt of washing-up liquid and then vinegar. You can experiment with different amounts of vinegar and powder.

Or try a mini version of Coke and Mentos. Take a small (250ml) bottle of diet cola, drop in three Mentos and decide if that’s the eruption for you!

My favourite is a much slower eruption but it just keeps on going for ages. This one needs some 6% hydrogen peroxide (available cheaply in all chemists, don’t use any stronger than 6%). Pour 100ml into a small bottle, add a good squirt of washing-up liquid and then add the magic ingredient: a spoonful of yeast mixed with warm water. The foam ‘lava’ is safe to play with, it’s just soapy water.

How do these work?

  • The vinegar and bicarbonate of soda react together because they are an acid and an alkali (see the colour changing cabbage experiments for ideas about this). The chemical reaction makes a type of salt, some more water and carbon dioxide gas. It’s the gas the makes it into an eruption, the washing up liquid just catches some of this gas to make a load of bubbles.
  • See the Fizzy Fountains experiment for ideas about Coke and Mentos.
  • The final eruption is called ‘elephant’s toothpaste’ as it looks a bit like a massive heap of toothpaste being squeezed out of a tube. The hydrogen peroxide can break down to make water and oxygen gas. It usually happens pretty slowly but the chemicals in yeast speed it up. All the gas bubbling up through the washing up liquid is what makes all the foamy fun!


We’re always told not to play with our food but sometimes it’s tricky not to! Here are some interesting investigations on food and our sense of taste.

Everything tastes the same!

Investigate how your senses of smell, taste and sight work together to help you enjoy your food. Get a few different fruits or vegetables such as carrot, apple, potato, turnip, parsnip or pear. Either grate or chop them into small pieces (all about the same size). Now get a volunteer to close their eyes and hold their nose while you feed them a little of each. Can they work out which is which? They probably can’t as you need all of your senses for your brain to identify a food. You could try different foods or different people (are adults or children better at this?). Apparently even strong-tasting foods such as garlic don’t taste any different from a potato if you hold your nose but I’ve never been brave enough to try! You could try chewing a small piece of raw potato while sniffing a piece of apple, does it start to taste of apple?

Multi-coloured celery

A boring old piece of celery can teach you lots about how plants work. Plants do not have veins and blood like us but they do have a system to move things around. They have special tubes called xylem vessels to carry water up from their roots to their leaves. You can see this in action if you put a stick of celery in a glass of coloured water (use food colouring). After a couple of hours you will see the colour has moved up the stem. If you cut across it, you will be able to see the xylem vessels clearly. You could try splitting the base of the celery stick and putting each half in a different colour do the colours mix or stay on their own sides? Try looking at other veg when you’re eating, can you see the xylem vessels in a carrot or lettuce?


You will need: an old CD or DVD (check before you steal your mum’s favourite Take That album!), a sports-bottle cap (Fruit Shoot or similar), a balloon, Blu-tack.

Roll the Blu-tack into a sausage and use it to attach the cap the centre of the CD. Make sure the cap is closed. Inflate the balloon but don’t knot it, then carefully stretch the opening over the bottle cap (it helps if you twist the end of the balloon to stop it deflating while you’re doing this). Your hovercraft is now ready to go! Carefully open the cap and the air will start to escape from the balloon. This makes a ‘cushion’ of air under the CD so you should be able to skim it along a smooth surface (the floor is best). Why not decorate your hovercraft and race it against your friends?

See how to make this on the Fab Science YouTube channel


Think like a scientist:

  • Try skimming it without the balloon (or with the cap closed), what do you notice?
  • The cushion of air reduces friction between the CD and the floor, can you find out more about friction?
  • Does the size of the balloon make a difference?


What happens when you poke a balloon with a sharp stick? Expecting it to go bang? Try out this impressive science trick to skewer a balloon without popping it (hopefully!).

You will need: balloons, bamboo skewers, vegetable oil.

First, inflate the balloon about half-way and tie a knot. Next, dip your skewer in oil to make it easier to push into the balloon. Now for the important part, choosing where to stick the skewer: look carefully at the balloon and you’ll notice that the area close to the knot is a little darker than the rest of the balloon, that’s because the rubber isn’t stretched as much. This means that if you make the hole there you might manage to avoid the ‘pop’. At the other end, there is another darker area, carefully push the skewer out at that point and you have a balloon kebab!

Note for parents: take care with sharp points and this should only be attempted under supervision. A cheap pair of safety goggles from a DIY store could come in handy.


Floating and sinking is all about density. We usually think about solid things floating or sinking in water. For example, a football will float on a pond as it is less dense than water and a bowling ball will sink as it more dense than the water. Using these same ideas about density you can make liquids float on top of each other with some very colourful results!

You need

  • a glass or clear plastic beaker
  • golden syrup (squeezy bottle is best)
  • washing up liquid
  • coloured water (use food colouring or fruit squash)
  • cooking oil
  • a spoon

What to do

First, pour about 1cm of golden syrup in the bottom. Try to avoid getting any on the sides of the glass. Next, carefully pour washing up liquid on top (try to pour it very slowly down the side of the glass). Do the same with some coloured water, even slower this time. Finally pour vegetable oil slowly onto the top, it’s easier if you run it over the back of a spoon. Hey presto, you’ve made a liquid rainbow, isn’t it pretty?

Think like a scientist:

  • What happens if you carefully pour a few drops of coloured water on top of your rainbow? (watch from the side)
  • Can you experiment with other liquids?
  • You can try making your own liquids of different densities by adding different amount of salt or sugar to water.
  • Which liquids are best for floating? Try floating the same thing in different liquids such as water, oil, juice, washing up liquid, golden syrup. Do some things float in one but not the other? Can we link this to the density of the liquid (think back to the rainbows)? This is a messy one but does you thinking about density! Good things to try are peas, small beads, marbles and sweets.

Don’t forget to show us your rainbows on the Fab Science Facebook group…we’d love to see what you have been up to!


Simply fill a small white plate with water (a few millimetres deep) and place a selection of Skittles or M&Ms around the edge. Keep it very still and watch as the colours travel across the plate. What do you think will happen when the colours meet? You might expect them to mix but you’ll probably find that you get perfectly neat lines instead! This is because the sugar and colouring that is dissolving from the surface of the sweet is spreading out by a process called diffusion. The sugar will move from where there is lots of sugar to places where there is less. When it meets more colour and sugar coming the other way, there’s no point going any further!


You can make your own colour-changing potion just using vegetables! You will need a grown-up to do the cooking bit.

Making the potion:
Roughly chop half a red cabbage and boil in just enough water to cover it for around 10 minutes. The water should turn dark blue. Keep the water and put the drained cabbage to one side. Leave it to cool.

Doing the experiment: You need some beakers (see-through ones are best). Put about 100ml of water in each one and add 2 tablespoons of the blue potion. Now get experimenting! Try adding different things to see if you can make the liquid change colour, you’ll need to give them a stir. Things you could try: vinegar, lemon juice, milk, liquid hand soap, toothpaste, bicarbonate of soda, washing powder… anything else that you can find (check it’s safe!). Try it again using beetroot instead of cabbage, do you get the same results?

Think like a scientist:

  • Try to guess what colour each one will go before you do it.
  • Can you change the colour back if add something else?
  • Have a look at the cabbage, what colour is it? Would you want to eat it? How could you make cabbage stay red when it’s cooking? (look up red cabbage recipes for the answer!)
  • The colours change because the things that you are testing are called acids and alkalis. Acids turn the liquid red or pink, alkalis make it go blue or purple. Can you find out about them in books or online?