Well, seems like the smallest symmetry order makes sense to use, I suppose. In any case these are 5-fold geometric patterns from the ‘Arts and Crafts of Islamic Lands’ book. They are all drawn on a decagon, mostly from the intersection points of the lines between the vertices. Here are the four:
Sharp eyed readers (if any) will notice that a) these are painted in acrylic, not watercolour (as the post title suggests) and ii) two of these patterns are the same. Foolishly I spent some time making the minimal version in a diamond shape, then tiled that, then realised it was the same as the other one. Ho, hum.
To pick one of them at random, nearly. This one:
Looks particularly nice as it has a fade from top to bottom as I gradually diluted the paint. Not deliberate, but looks quite nice. Oh, and these are all outlined in fine pen (0.1 to 0.5 mm) to contrast the colours.
The final product is here