So, i’m not entirely sure of your process but heres what i would recommend. I do this when painting warhammer figures. After you have the model finished, give it a signle very light coat of flat black primer spray paint. Then when painting it, thin your paints with (if you’re using a water based paint) water. If you’re using oil, well, i’m not 100% sure. Check out some warhammer painting tutorials on how to thin your paints, it will increase the already pretty good quality of this type of paint job