According to Cosmetics Historian James Bennett: “In the early 1930s Lady Esther became the top-selling, loose face powder in the United States, a position it maintained for the rest of the decade” (Bennett, 2018) She created that position by promoting her product as the very finest and confirming it with a home test: “Take a pinch of your powder and place it between your front teeth. Bring your teeth down on it and grind firmly. If there is any trace of grit in the powder it will be as instantly detectable as sand in spinach.”(Lady Esther advertisement, 1935)
This was so successful that competitors needed to find new processes and new materials in order to pass the “bite test”. In 1937 chemists started to do research on particle size required to pass the test. One such chemist, M. L. Smith published the results of his experiments on volunteers. As reported by deNavarre, Smith determined that the particles would need to be 12 microns (0.012 mm) or less to pass the test (deNavarre, 1941, p. 354). This was much smaller than the particles produced by the mixing and sifting methods then used by most powder manufacturers. (Bennett, 2018)
“It must be remembered that a “fine powder” is, of course, a relative term. A generation of so ago “200 mesh” was considered very fine. Nowadays a 50-75 micron particle seems rather coarse, and a material needs to be below 10 microns in size to be thought of as an “impalpable” powder. Perhaps in another twenty years even particles of 10 microns might be thought of to be boulder-like, and the public demand may be for something finer still.”
(Hibbott, 1947, p. 271) (Bennett, 2018)