Fluorescent food dyes

We have used my collection of food colourings for a few previous activities, including mixing primary colours, making colourful sugar gradients and using the yellow curcumin-based food dye to make colour-changing fabric for acid and alkali art. This time, I thought we could combine learning a bit more about ultraviolet light and fluorescence with some tie dyeing to make it more fun!

The food colourings we used (Tesco own brand if you're in the UK) contain the following key ingredients:
- Yellow - curcumin
- Red - anthocyanins
- Blue - spirulina extract
- Green - curcumin and spirulina extract

The fabric we used was a piece of white cotton jersey material cut from an old Moses basket sheet which had shrunk in the wash. To do our tie dye, we did the following:
1. Took the square of material, put the handle of a wooden spoon in the middle and twisted the spoon to coil the material around the handle. With the assistance of my small boy, this took a couple of goes to get a fairly even spiral.
2. Removed the spoon whilst holding the material in place and put two elastic bands around it, at right angles to each other. The small boy liked making this into a 'present shape'.
3. Made up concentrated solutions of each of the four food colourings, approximately one part food colour to three parts water.
4. The small boy poured each colour onto one quarter of the bundle of fabric, between the elastic bands. He needed encouragement to do this slowly so it had time to absorb into the fabric rather than running off.
5. Left it in a plastic box for about 8 hours.
6. Washed it. I stuck it in the washing machine as we have a super quick wash that uses a small amount of cold water. Do not put it in the wash with anything else!

Fabric with dye added

I wasn't sure how well this would work - it was a bit of an experiment in how well the dyes would bind to the fabric. However it worked brilliantly and we ended up with a lovely tie dye spiral pattern which the small boy liked!

The next part was to put the dry fabric into our home-made UV light box. The food colourings fluoresce, absorbing the UV light and emitting it in the visible spectrum. They don't look the same colour as they do when illuminated with white light! The small boy quite enjoyed looking at his fabric pattern under the ultraviolet light and telling me about the colours he could see.

Tie dyed fabric illuminated with (L) white light and (R) ultraviolet light

This was a nice combination of showing how a spiral shape can be made and talking about more fluorescence following our experiment with highlighter pens (which we've done a few times since with different drawings as it's proved a good way to get the small boy doing some mark making).