Oyster underpainting

I like to layer my paintings, it gives them more depth and interest. The first layer is a value study. I choose a color to compliment the main colors of the finished painting. Since the oyster will have a lot of blues, I chose transparent red oxide which is orangish, the complement of blue. It's my favorite color for underpainting, as it is transparent, so it glows in the lightest areas and is dark enough to give me a dark, but transparent value. I use only transparent red oxide and a solvent to create this layer, no white is allowed, it will cloud things up. Using a black and white copy to isolate the lights and darks, I paint in the values, heavier on the darks and thinner on the lights, wiping out the whitest areas. This step is done in one sitting, because after it dries you cannot reclaim your lights. The trick is to match your values with your next, color layer. I also like to let the under painting peek through to infuse the painting with a cohesive color. If it works this layer glows and looks so good, you don't want to cover it with color, but be brave. It gets better.