Mica may be cemented by moistening the edges with a solution of gelatine in strong acetic acid. Another cement for mica is made by soaking gelatine in cold water and pressing out excess of moisture in a cloth. Then heat it on a water bath until it begins to melt, and stir in alcohol to form a fluid. For each pint of solution, gradually add whilst stirring 1/4oz. of gum, 1 1/3 oz. of gum mastic previously dissloved in 4oz. of rectified spirit. Keep in stopper buttles, and warm when required for use.