Example 1 0.7 lb. of casein is stirred into 2 lbs. water. Stirring is continued while 3 lbs. of 28 wt. percent aqueous ammonia are added and the stirring continued for about 20 minutes to dissolve the casein. Then 8.5 lbs. of a 10 wt. percent solution of cooked starch are added with thorough stirring. Then 7 lbs. more of the aqueous ammonia are added and the solution made up with water to a total weight of 96.5 lbs. Then lbs. of finely ground plaster of Paris (steam calcined. gypsum) are stirred into the solution and finally 3.5 lbs. of finely ground ZnSO 6-H O are added and the whole mix thoroughly stirred.