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Hi. There are markers that are made for small children that only shows up on a special peice of paper. If a kid draws on a wall no color is produced. Crayola calls them "Wonder Markers." How do they work? Thank You.
Question Date: 2010-05-31
Answer 1:

Most of the wonder markers rely on molecules called Leuco Dyes. These dyes are very similar to a pH strip. If you haven't seen a pH strip before, it is a piece of paper with a dye in it. By putting the strip into solutions of different pH's, the strip turns different colors.

The way that I imagine the markers work is that they have different pH sensitive dyes that are clear at their pH of storage - maybe its neutral. I imagine that the special paper is either acidic or basic, which will cause a change on the dye molecule, causing color to appear, just like with the pH strip.

Those markers aren't just for small children! They're still fun!

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