Purple Brazilian Clay

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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!
 
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I remembered that I have 150 ml syringes sitting around the house for some long gone soaping idea. It was easy to collect the clay-laden water from the jars leaving the silt layer behind. A siphon hose would also work.

It looks like jar on the left has mostly suspended clay with little to no silt remaining. The jar on the righ has most of the grey silt that was in the mixture.

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Next up will be the Blue Cambrian clay because it also seems to have a lot of impurities.

Here’s the blue clay. There’s a super thin, gorgeous blue layer near the bottom of the middle jar. It may be easier to see it in the second photo.

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Now I’m going to be patient and let gravity do its work.
 
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Thanks @Zing I like them all, but it would be nice to get just a tiny bit more color out of the clay. I didn’t want to add more because of the grittiness, which is a bit much in the product I purchased.

I mentioned Nurture earlier, which is where I get my micas, but the clays came from a Etsy seller. They’re sold as “premium cosmetic clay“. The color of the clay aside, after seeing how much sand is in the mix, I will not be buying from that seller again. (edited to add: in the end, I like the colors I got enough to buy at least the blue clay again, assuming it performs well in the test bars I made, which are posted, here). The purple clay from Nurture looks better online and in this gorgeous soap. It is possible to get much purer blue clay, but perhaps you have to know someone or live in Germany! Fraeulein Winter used it to make a pretty polka dot soap.

I realize that this post is getting to be a bit like an elementary school science experiment. If you’re still following along, great! I’m having fun playing with mud.

The purple clay is coming along nicely, but is starting to look like it has a good dose of rose colored clay. I succeeded in eliminating most of the larger particles.

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I’m still working on size fractionating the blue clay. The jars below are pint size versus the quart jar above and I started with 2x as much blue clay (4 tbs) compared with the purple clay. There won’t be much of the deeper blue, but I’m hoping to have at least enough for a nice swirl in a white soap. I have about a quart of the light blue (second from right) in suspension and put most of it in a warm oven to speed up water evaporation.

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Updates!

I’m almost done with size fractionation of the clays from the purple Brazilian “clay” mixture. First, I ended up adding in the rest of what I had, just under 4 oz. total. Once the coarser particles and grey silt were removed, there were two major fractions left. The one that settled first is an ultramarine violet color (in the bowl). That left a pretty pink fraction and some white clay in suspension. The white settles the slowest and was siphoned off before I took the photos. The jar on the left in the second photo has the purple and pink fractions layered at the bottom over top of some pesky grey particles, the two in the middle are the pink-colored clay and the jar on the left contains rose clay for comparison. There is a bright deep purple fraction in this clay, but there’s not enough of it for me to recover using my crude methods with the small amount of clay I have.

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Fractioning the blue clay turned out to be more of a challenge, even after I mixed in the rest of what I have, so nearly 4 oz. total. Most of darkest blue particles settle out sandwiched between two grey layers, which is very inconvenient. The almost pure version of that lovely blue, in the tipped pint jar, is the color of ultramarine. There’s also a layer at the bottom of the jar to the right that is still sitting on top of a pesky grey layer. The second set of three jars shows various splits of water off the top of the settling jars. I added a bit of sea salt to each jar to make the clays clump and settle more quickly. As it stands, I have dark blue, pastel blue, lt. blue/green/grey and grey clay fractions, plus some pumice-like silt.

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If you want to try a less complicated method to remove the grittiness from your clays, check out this post:
 
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Can the rest of us get such screens? If so, where?
I’m using Nitex bolt cloth that is < 63 um, likely #230 mesh. I lost track of the exact mesh size when the labelling rinsed off in a close encounter with isopropyl alcohol. #230 mesh will retain sand, and let the silt and clay pass through to a collecting container below. It’s widely available through scientific suppliers and possibly on Amazon, but there’s usually a 1 yd minimum and it’s pricey due to the nature of the production process that ensures calibration.

You can also buy ready made stainless steel sieves with calibrated mesh, but they’re also expensive.

A search for #230 mesh on Amazon turned up polyester silk screen mesh that is close, like #200 or #250. It’s inexpensive and may be worth a try. This #200 stainless mesh also looks reasonable. https://www.amazon.com/dp/B081QB3BLF?ref_=cm_sw_r_ud_dp_Z7X112DYZXNEY530P57F

A handy mesh size conversion chart:

Note: edited to correct the sentence in bold above.
 
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It’s taking quite a bit of time to get the bluest clay out from between the two pesky grey layers, but I’m almost there. Actually, one of the pesky layers is brown and one is grey. That has led to some nice color variations in the portions that are mixtures of grey or brown and blue. The brown clay has maybe just the tiniest hint of green in it. I’m sure Van Gogh was with me late last night when I grinding dry clay in a mortar and pestle. Here’s what I have and will post the rest, including the priceless purest blue, when I’m finally satisfied that it’s as pure as I can get it. The bit of grey daylight isn’t the best for photography, but the clay colors look true on my iPad. It appears that I retained somewhere between 50% and 75% of the original volume, after tossing the very gritty sand fractions for each clay type. For context, the small jar caps are from recycled mica jars (5 gram size) and the actual jars, not shown are about 1/3 full. The glass jars are the 2 oz. size. I was not interested in weighing everything.

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Edited to add the last of it.

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left to right: first is the jar from above for comparison, next is the purest blue I was able to achieve, last is what I had to scrape off the top of the bluest fraction to eliminate a thin layer of brown clay.

The Great Clayscapade is over until the soap is made. I’m almost afraid to use it!
 
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paradisi

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Especially would like to see a chemical assay. It seems if there were a clay of that brilliant blue it would have been refined for ceramics use in Europe for decades if not longer.
Plus, IIRC, that Cambrian clay used to be touted for its radiological "health benefits". So... I have questions.

I've seen the assays on the purple clay, nothing hinky there.
This is SO COOL… I have some Cambrian blue clay that I don’t trust - when you say you tested to make sure the colors weren’t from a dye, how did you do that?
 
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This is SO COOL… I have some Cambrian blue clay that I don’t trust - when you say you tested to make sure the colors weren’t from a dye, how did you do that?
There was no color change or release in water, alcohol or 50% MB lye solution. I did not try an acid, but probably should, but see below.

@paradisi - The COA is available here and the MSDS is available on request from seller. Blue clays are common in nature where they are formed under conditions that leave iron in a reduced state. They are being studied for use as medicinal clays. Apparently there’s a big deposit in Oregon. Check out the third photo down, here.

Edited to add: There are at least two blue fractions in the material I have. The particles that formed the very bright blue settled pretty quickly (minutes). That fraction may be in the fine silt range and possibly quartz based, which could account for the color. The other predominant blue fraction settles very slowly (days) and must be a very fine clay. And then there’s everything in between.

Edited again:
Curiosity got the better of me. The bright blue in the mix is probably Dumortierite, which is indeed a quartz mineral. There are mines in the Uvil’dy Lake region of Russia, which is the source of the clay, according to the seller (more here, use a translator). According to Wikipedia, the stones have been used as imitation lapis lazuli.
 
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I have a couple of blue clay updates to share. First, I contacted the etsy seller to ask him what else he knows about the clay. He responded, but provided little information except that the clay he is selling now is more finely milled. Perhaps that means it no longer contains sand, which would be great. Further research on blue clay led me to the French blue clay D’Argile Bleue, which I can‘t locate for sale in the US. As luck would have it, I made a new friend last weekend who just so happens to live in Paris. She researched the clay for me and learned that it contains azurite, a copper-containing mineral. I’m not sure how it will behave in soap, but she is going to send me some for testing.
 

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