6/8. Red onion, oil on linen panel, 7x5 in.
I began to understand just before this painting what the difference between Mars and ivory black is. I never really thought much about black, always treating it as a minor hue (though it's not really a hue) unlike in the limited palettes where it plays a very major role; sometimes I'd use it only for making an already dark color blacker. (Usually when I said "black" I meant Mars, always believing it to be darkest.) Though I say Mars is blacker overall - i.e., it's opaque and stronger - ivory black is actually blacker, i.e., darker. The main difference is that ivory black is semi-transparent. So I thought, with my palette's dark hues being transparent (or semi-), would I generally want to go to a black that is semi-transparent as well?
I assumed mixing a transparent black with already transparent darks wouldn't have any real additive effect. In fact I didn't think about the subtractive effect it would have, i.e., the paint being too oily - as can be seen in the upper background of this painting, which was the result of switching to ivory black for a mix. Putting some Mars black in it towards the bottom made it stronger, but I left it mostly as it was here because it was interesting.