I have bought coloring books for my son. The book has pages of pictures what turn to color after you brush it with wet sponge ar brush. How does it work?
Also, some of them are single use only – you get them wet, they stay colored. Other (more expensive ones of course) dry out and you can re-wet rhem again after some time. How does thaaat work?
In: Other
They have the paint under water soluble covering. when you apply water, the outer disolves and you then get the paint to fill the area
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