The purple Brazilian clay I bought makes soap that is much more grey than purple. Here’s a comparison of an alkanet test bar from last year (left), and two bars made a couple of months ago. The center bar is purple clay at 1 tsp clay ppo, and the right bar was made with ultramarine violet.
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This morning I decided to wash the clay in an attempt to reduce the grittiness. Look at all the very fine dark brown sand that was in a couple of heaping tablespoons of the “clay.” I removed the larger particles, which is the stuff in the white dishes, by rinsing the clay through some very fine Nitex mesh screen borrowed from a science lab. The mesh is used in soil analysis and for size sorting very tiny planktonic animals and algae. I’m not 100% sure of the mesh size, but I’m guessing it’s around 63 um, which is close to the cut-off between sand and silt-sized particles. If you look closely at the jars, you can see that a grey silt layer settled out from the fraction that went through the mesh screen. The colorful clay fraction is still suspended in the water. In case your wondering, I’ve already tested the clay to make sure that the color isn’t due to a water, alcohol or lye soluble dye. My next step will be to try to decant the suspended clay without disturbing too much of the silt. It will be interesting to see what percentage of this powder is actually in the clay particle size range. The silt fraction feels a bit finer than fine pumice and will be fine for exfoliating soap. It’s likely that I will discard the sand.
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edited to add some facts:
Most of the micas I use are from Nurture soap. They often fall in the 10-60 um size range, which puts them into the size range of silt, according to the
Wentworth Scale. The ones that remain shimmery even in cold process soap are more like 200 um. Clay-sized particles are 3.9 um or smaller and will eventually settle. True colloids are 5 nm to 0.1 um and they stay in suspension under normal conditions. Bacteria are typically around 0.5-2.0 um and viruses are smaller!
