Glycerine is available in your local drug store. It has the consistency of oil, somewhere between water and honey in viscosity. It is water soluble and takes a long time to dry. I use it primarily to mix with acrylic paints to slow down the drying time. In one case, the paint was still tacky months later. While acrylic paints usually dry within ten minutes, a drop (say, one part glycerine to four parts of acrylic matte medium and two parts paint), will slow down the drying time to about an hour, depending on the thickness of your paint. You can work with acrylics as you would with oils, depending on the amount of glycerine added. Some expressed concern that glycerine would affect the permanence of the finished painting. I discovered that "glyceroids" are an ingredient listed on tubes and bottles of acrylic paints and mediums, and so I feel fairly confident in using it as a medium and slowing agent. Often there is a clear liquid at the top of acrylic paint in the tube or bottle, and I suspect that this is glycerine.