Here is Extenders very useful to make the paints flow better and extends drying time so you can work on the blending and highlighting a longer time to get a smoother surface. I mix this into a bottle about 15-20% each and then the rest distilled water. I find Liquitex Slow-Dri Fluid Retarder and Flow-Aid to be the best. About $6 a bottle it will last you long. There is also a cheaper choice Anita's Extender for about 90 cents at hobby lobby.