I'm doing a portriat with these paints and while reworking on the face i find the paint is sticky and some is rolling into little pill like things. I like the skin on my portriats to look flawless and smooth. i do not want bumps in the paint. I'm using the paint with the aqua oil. Using reeves and Winsor and newton brand. Should I use regular oil to mix, thin these paints instead of the auqa oil? could I still clean up with water?