Here's The Answer

Popular Science, kesäkuu 1935

Coal as a Source of Colors
P. J. S., Suite, Mont. About 900 different kinds of dyes are made from coal tar. The first one to be discovered, in 1856, was mauve. Coal is therefore of the utmost importance to the drug and dye stuff industries.

'Perpetual Ink'
D. L. K., Los Angeles, Calif. "Perpetual ink" can be made by melting three pounds of pitch over a fire, and adding three-quarters of a pound of lampblack. Sir the mixture well. Its chief use is for filling in letters carved into marble, granite, or some other stone.