These inks are supposed to be invisible unless activated by light or heat, but in practice, you can usually still see a little bit of what’s written with the ink.

Geek Life: Fun stories, memes, humor and other random items at the intersection of tech, science, business and culture. SEE MORE Lines drawn with Living Ink’s algae pen disappear in about 10 ...

“Mix 5 drams copper acetol arsenate. 3 ounces acetone and add 1 pint amyl alcohol (fusil-oil). Heat in water bath — steam rising will dissolve the sealing material of its mucilage, wax or oil.” ...