I took up paint-by-numbers recently and was struggling with paint drying out as well as coverage issues. I was amazed when I started adding this to paint. A few drops in each mini tub of paint works miracles to guarantee better coverage. I really don't know how this works but instead of thinning the paint, like when I added water, it seems to thicken it making covering numbers and lines effortless now. Wish I could go back and redo all the paintings I've done before I used this product. Now I'll just have to buy my favorites again and make them better.The smoothness of the paint and the color sustainability is absolutely wonderful! This size bottle should last a very, very long time and I couldn't be happier!