Science talk With Chris Duggan House of Science

With Valentine's Day coming up, homemade cards and gifts are always better as they come from the heart, and what better way to celebrate Valentine's Day than with a Marbled card that combines your skills in both art and science?

Please note – this is a messy activity, then again, all the best activities are when you are allowed to get messy on purpose and it's for a good cause – putting a smile on someone's face – your mum, dad, or a partner.

Equipment:

• Two large plates
• Shaving cream (foam not gel)
• Food colouring (a minimum of two different colours)
• White Paper/cardstock
• Scissors
• Spoon
• Toothpick
• Paper towels
• Spray bottle with water

Instructions:

1. Spray a pile of shaving cream on the two plates and spread it out using your hands or a spoon to create a layer with an area at least as large as your card and a depth of about 1 cm.
2. Take the first bottle of food colouring and add several drops to the shaving cream. Do this with both plates.

What happens to the food colouring once it drops on top of the shaving cream?

Does it sink, mix into the foam, or stay on top?

3. Repeat step two with the other colours of food colouring.
4. Take the toothpick and carefully swirl around the colours in the shaving cream until you have created a colour pattern that you like. Try not to overmix the colours.
   What happens when you swirl the colours around?
5. Do they mix with the shaving cream, or do they separate?
6. Using the spray bottle, spray some water on top of the colour pattern on one of the plates. Use at least 5-10 pumps of water, then let the foam sit for about one minute.
7. Finally, place your first card with the front side facing down on top of the ‘wet' shaving cream and press lightly so that the whole card is covered in shaving cream.
8. Repeat step six with the second card and the second ‘dry' shaving cream plate.
9. Carefully remove both cards from the shaving cream, turn them around, and using the paper towels, scrape the remaining shaving cream from the card.

What do you see on the paper once the shaving cream is removed?

Do you notice a difference between the two cards?

Can you explain your results?

10. Let the cards dry. If the paper wrinkles, you can ask an adult to iron it with an iron on the lowest heat setting – if doing this, please place another sheet of paper between your card and the iron as you wouldn't want to destroy your amazing piece of work.

The Science:

Shaving cream is made of a mixture of soap and water with a gas that turns liquids into foam when you spray it out of the bottle. Soap is a surfactant, which means its molecule has a hydrophilic
(water-loving) and hydrophobic (water-repellent) end. Liquid food colouring is a mixture of dye in water or alcohol and therefore is hydrophilic. When you drop the food colouring on the shaving cream, it won't get soaked in, as it only interacts with the hydrophilic parts of the soap molecules and is repelled by the hydrophobic parts. Even when you swirl the colours together, you will see a distinct separation between the colour and shaving cream.

When you put the paper on top of the colour pattern, the food dye gets soaked into the paper, transferring the whole pattern onto its surface. This is because the paper is made from wood pulp and contains cellulose found in the cell walls of green plants: a hydrophilic molecule. The hydrophilic food dye can spread easily across the paper, creating a beautiful, marbled look.

One Step Further:

What do you think will happen if you spray oil instead of water on top of your colour pattern? Try it and see if your prediction was correct.