I'm currently working on a large commission. There is a lot of black. My issue is some of the black is shiny and some of it isnt. It's drying very strange compared to what I'm used to. I feel like part of the issue is parts of the painting is thicker paint than the rest. Could that be the cause? I' going to start on a new canvas what can I do to prevent this as much as possible. I don't mind if it does it a little. But it looks pretty bad.