The method of testing the quality of plaster of Paris is by taking a small pinch of the powder between the finger and thumb and gently rubbing it, if small particles of it are felt, grit indicates that, parts of the plaster have already absorbed water, and it is therefore unfit for use. The same test may be observed by taking a pinch of the powder again and placing the fingers under water, and then rubbing the same way as before. If, however, in both of these tests no grit is felt, and under water a thin creamy substance is found, which is easily rubbed off the fingers, the plaster is in a proper condition for use.