Another art package I was using a lot last year is ArtRage oils, a free drawing app where the pens in it look like oil paint that can be adjusted to look more or less metallic. The difference with it is the ‘painterly’ effect is more pronounced and more difficult to control. There is not really the precision of other apps but it makes up for it with robust colours. There is a paid for version has more pens and tools, so gives you greater variations and the ability to go to town on interesting images.