Since I'm not much of a painter, I've continued my value studies with the Munsell Student Color Set using my Prismacolor markers.
Prismacolor makes three different gradient grey color marker sets: french grey, cool grey, and warm grey. I have the french grey set. The cool greys clearly have a blue tint. Looking at the samples on my monitor I don't see as much of a specific color tint in the warm greys - maybe red, but if so it's very subtle. The french grey set clearly has a yellow tint - so at this low chroma it appears most like taupe. Though without any other color in context, the yellow is barely noticeable.
Like the value scale Deb Menz uses in her book, the Prismacolor grey scale is based on the percentage of black that is mixed with white. So the lightest marker is 10% and the darkest non-black marker is 90% and there are nine markers in the grey scale, plus black. As you might be able to tell, my 50% marker has seen better days. I should really buy a replacement.
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One difference between opaque paint and the ink in Prismacolor markers is that you can build up layers of ink in such a way that the value and chroma change. These last two images are samples I made layering the 10% French grey and 20% French grey respectively. I found that by the fourth layer of the 10% French grey, the value matches the 20% French grey. So you can layer the 10% French grey to create two values between 10% and 20%.
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I also need to line up my other value indicies to see what Munsell values apply to which Prismacolor values and what Menz values apply to which Prismacolor values.