Spinach sun print paper

As a child I had a pack of paper which changed colour when placed in sunlight.  I remember making prints of various objects, but mostly of treasuring the pack of paper in its little blackout bag and thinking of things I could use it for.  I had a look at something similar for my son, but it's pretty expensive for something that he may or may not find interesting so I decided to experiment with making something similar to see what he made of it.

Chlorophyll, the pigment that gives green plants their colour and enables them to photosynthesise (convert energy from sunlight into chemical energy) can lose its green colour in strong sunlight (photobleaching).  This gives a green to white colour change.  For a source of chlorophyll, I used spinach.  You could use any green leaves, particularly dark green ones which have high concentrations of chlorophyll, but I went for something edible.

To extract the chlorophyll, I used a pretty crude method, but it worked.  I put some spinach leaves and a small amount of vodka into a blender, whizzed it until the spinach was very finely chopped and then strained the liquid using a small sieve.   I didn't know if the vodka would work as chlorophyll isn't water-soluble, but there seemed to be enough ethanol (alcohol) in there, so my guess is that any colourless high percentage alcohol spirit would be fine.

I then painted the dark green liquid onto some printer paper with a sponge brush (a normal brush would do, but this gave a nice even covering) and let it dry.  I put it in the oven an hour after dinner was cooked so it was a bit warmer than room temperature.  It might be stating the obvious, but don't put it outside to dry in the sun...!

I experimented with a piece of the paper to see how long it took to change colour.  It was a very sunny day, and after an hour there was a pretty clear colour change where it was exposed to the sun.  To make a nice print pattern, you need something which will stay still and not allow light through.  You could use a piece of glass to hold light-weight objects e.g. leaves on the paper and allow light through, but I went for something which was easy and hands-on for my 3 year old.

Making a robot design

He loves all things robot-related, so I dug out the spanners and other bits and bobs from the toolbox which he'd used for his slime robot creations, together with a few coins.  I explained that the paper would change colour in the sun and that he could make a picture by putting things on top of the paper to stop the colour change underneath them.  I suggested he might like to make a robot, or something else if he preferred.  He wasn't quite sure about the idea of the colour-changing paper, but the idea of making a robot appealed and he set to work placing the loose parts on the paper, which I'd placed on a tray so he could assemble it slowly indoors before moving it into the sun.

He decided to use absolutely everything I'd put out, and chattered away about how it was going to be a money-making robot.  I wish his creation was real, but I enjoyed watching him having fun making shapes and moving them around until he was happy.  We then carefully carried the tray between us into a sunny spot in the garden and left it there for 45 minutes whilst we did something else indoors.

His 'money-making robot'

He wanted to have a look to see if anything had happened, and at a first glance he wasn't impressed.  I suggested that he carefully lifted a coin to see if it was a different colour underneath, and when he discovered that he could see where the coin had been because there was a dark green circle, he wanted to see the rest of his robot.  It wasn't totally even, possibly because I didn't paint the chlorophyll mix on evenly or possibly because of the angle of the sunlight.

We took it inside (so the pattern didn't fade) and took all the loose parts off the paper.  He was pretty happy with his sun print picture, and told me all about the robot's money-making abilities!  We found a place to put it up which doesn't get any direct sun; over a week later it's not faded noticeably.

I explained that I'd made the colour-changing paper with spinach leaves, and showed him the left-over chlorophyll mixture.  He wanted to make some more, which we duly did, although it had to air-dry and he'd lost interest in making another picture by the time it was dry.

Sun print picture of the robot

The solar paper I had as a child could be fixed by putting it in water, and the stuff I made will eventually fade.  However it provided some amusement, and we may well come back to it this week as it's forecast to be sunny again here.

Comments

  1. Wow this sounds brilliant. Can't wait to try it out with my son soon. As a chemistry nerd who also likes plants and biology, chlorophyll is fascinating, and this application is too. Well done!

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    Replies
    1. Thank you Hannah, I hope you and your son have fun!

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