Q: I know what type of medium to add if the paint coming out of the tube is too thick. But what if the paint is too thin?
A: One way to alleviate this problem to some extent is by
squeezing the paint out onto an absorbent surface such as blotter
paper. With a painting knife, move the pile from one to another one the
blotter paper in order to absorb as much oil as possible until the
paint has the desired consistency. In doing so, you might find that
after removing some of the oil, the true amount paint of in the tube is
less than you had originally thought. Therefore, investing in higher
quality colors may prove to be more economical in the long run.