Golden Open thinner was made to better thin open acrylics without using water. As it thins Open acrylics it will also slow the drying time. Unlike GAC100 that we often use to thin regular Golden acrylics, Open thinner is water-based and has no binder in it. If you want it to act like binder and medium, you can mix it with Open acrylic medium in 1:3 ratio.