Why can't I make invisible ink out of lemon juice?

Question

I'm teaching a summer science class to kids and I try out the experiments the day before. Tomorrow, I'd like to make invisible ink using lemon juice and water (though I've tried with just lemon juice, too.) I've let them dry and then tried holding them up to a light for several minutes. I've also tried blow drying them, but nothing is revealed. What am I doing wrong?

Answer 1

You have to hold the paper close to the source of the light. It isn't light per se that makes the juice visible, it is heat. If you hold the paper with the dried lemon juice a few inches from a 100 watt bulb, you will get the desired effect. Just don't touch the bulb with the paper or it may ignite. You can also do it by holding the paper a foot or so above the burner of an electric stove. Use full strength lemon juice. Don't add water. You can also try it using milk instead of lemon juice.

Answer 2

You are doing it wrong, you are trying to do an acid base reaction with acid neutral chemistry. You can use lemon juice and milk to get a reaction, or vinegar and ammonia. You need two dissimilar liquids to stain the paper.

Answer 3

It's a blacklight you need not a regular light.....