The February, 1933 issue of Modern Mechanix included this great, long article on the state-of-the-art of horror movie makeup.
All the information he could dig up gave only a suggestion, not a solution of Pierce's problem in turning Karloff into a duplicate of Osiris for "Im-ho-tep," in which picture the mummy comes to life. Manifestly embalming fluids and perfumes have no place in makeup for the camera, so for a month Pierce experimented with pigments, paints, drying materials. He had to have a rotted cloth that would not fall from the body, yet would crumble easily when the body stirred from its coffin. The face must look very old and withered and dry. The eyes must be closed, yet seem to see.
An assistant spent a week feeding double-weight cheese cloth in two widths–two and three inches–through a barrel-like cylinder over a gas flame, winding it gently over a turning wheel. This cooked and charred the cloth without actually burning it.
Pierce experimented with 20 dry colors until at last he looked down into his mixing pot on exactly the yellow-gray color with which good mummies are covered. Burnt umber, light umber, fullers' earth, other colors, glue and hot water combined to produce this mud-like substance. With a little cotton and the standard make-up pigments Pierce was ready for the big job– a seven hour ordeal–of turning back the pages of time 3700 years, all for a five-minute effect on the screen.