Extender is used when you want to increase the work time of the paint. Add 1/4 bottle of extender (15ml) to 1 pint (500ml) of Fusion Mineral Paint to increase the dry time. Using this ratio 1 bottle is good for 2-4 pints of paint. Extender can also help reduced the apperance of brush strokes and roller marks. The more Extender you use the longer the dry/ cure time.