Black Shale

It has been awhile since I have worked on any new pigments. The black shale in the photo is from a mineral sample, that I took last year and had not gotten around to using. A small outcropping had caught my eye while I was in the mountains about four hours to the west.

I didn't know very much about my sample, so I wanted to be sure that it would be suitable for use in oil paint. I consulted a local geologist, who suggested that I take a pH test of the sample.

After I ground the raw sample, I mixed some with a small amount of water for the pH test. The pH was about 6, slightly acidic. I chose to go ahead to put the sample through my usual process of grinding, washing and levigating. Then I will try mixing it into paint.