John, For paints I've also used the testors model paint in the past. Look for it with the model cars in a craft shop, wally world, etc. If it has dried more than a day, it can be coated with epoxy. For painting I've used the butt end of a drill bit or tools made from a 1/4" dowel using a pencil sharpener. What I've found works for me is to shake up the bottle and then dip the stick or drill bit in the paint stuck to the jars cap. otherwise you get too much paint. I'll have to try the comb trick. I've used slits in pieces of corrugated cardboard to do the same idea before.
Mark, You've been a busy boy with the warm water patterns. They look good.