Even though I've revisited the earth formula here, I never really managed to make a true "formula" - one that could be replicated time after time, using precise measurement. As a result the various earth patches done so far on the layout vary in various degrees. Since I've been having a hard time matching colors with different batches lately, I've decided it's time to take things further and bought a precision scale. It can measure in increments as small as 1 milligram, so hopefully this will be good enough to replicate various dry pigment formulas over and over again. At 20 pounds, it's actually a good price - considering it actually has that 1 mg granularity observed after some testing. The photo shows this little device at work, while I was adding small amounts of ultramarine blue to the old earth formula (5 parts plaster, 1/5 parts burnt sienna, 4/5 orange). This has to do with a small test board made from a piece of foam and a sheet of plaster cloth applied on top - its role being that of sampling various combinations and writing down the various ratios involved.
Why blue pigment instead of pure black one to make the formula slightly darker ? 2 reasons: the complementary color of the light brown-ish color that my earth formula has is actually blue, as seen here (a hue plus its complementary color will yield black in color theory when applied to pigments as stated here), secondly, I've never experienced this combination before (I've been adding only black pigment until now).
