and only grind a very small amount at a time. I have ground it in a glass bowl I used as the mortar and with a wooden spoon as the pestle I have ground powder down to a very fine grade. I did this when I was testing substitute powders in a flintlock and wanted to see if I could make it all work. I even thought of getting my a real glass mortar & pestle and seeing if the extra fine powder would really make a difference in the speed of the ignition.