Making pigment from earth materials?

[High-Desert]

I have attempted to make earth pigments from some local strat layers, an incredible green, that I have to take a canoe out to get, so I would like to get a bunch and store it.
I grind them in a mortise and pestle and separate the sediment in water. Whenever I drain off the water after all of the fine sediment has settled, I let it dry......then its hard as a rock again and it no longer fine sediments. Has anyone else had this problem or am I missing some step here. The only way I have gotten it to work it to keep the fine sediment wet and mix it that way, but I would like to store it dry.

[Pat B]

Eric, can you grind up the dried sediment again?
 Is it copper that makes the green pigment?

[High-Desert]

I can grind up the dried sediment again, but I have to repeat the whole separation process again, it doesn't simply break down to a fine sediment.
I don't think it's due to copper, I think it's due to ferrous iron in a anoxic environment.

[Zuma]

Just a thought. If you repeatedly grind the material perhaps you will eliminate the binder
that creates the cement. Also maybe an additive could help diffuse the particles. 
From what I have studied is the blues and greens from nature are most always copper
related and iron the reds.
Zuma

[High-Desert]

Thank you  Zumba, what sort of additive should I use. I'm really new to the earth pigment stuff.
I would typically assume cooper too, but i did a lot of field study in this area for my geology degree and we have layers of oxidized iron, which causes the red color, and the anoxic layers of iron can cause green to green grey. Cooper is typically more on the green to green blue....but when identifying rocks, color is usually the last identifier.

[TrevorM]

A total guess, but could it be green clay?

[Zuma]

Oil is cheap.  Citrice juice, turpentine? Chemistry is my short suite.
Zuma

[High-Desert]

yes, it is definitely a clay material with some larger clasts. I will try some different additive to see if it helps.

[TrevorM]

OK if it's clay you could bake it first to harden it. Then it wouldn't be water soluble any more. The only issue I can see is the high temps might change the color. Maybe you could just heat it in a hot oven instead doing a full kiln?

[High-Desert]

Baking it! That's a great idea! Thank you TrevorM

[TrevorM]

I have them once in a while Let us know how it goes 

[Jodocus]

With a decent mortar, you can even grind down rock. If you do it dry, some will fly off, but it sounds like you have plenty.