DROPLETS OF AN AQUEOUS SOLUTION OR SLURRY CONTAINING A POTENTIALLY TACKY SUBSTANCE ARE SPRAYED OVER A POWDER BED OF A REFRACTORY MATERIAL PREHEATED TO ABOUT 200*C.700*C., WHILE PRECAUTIONS ARE TAKEN TO INSURE THAT THE DROPLETS DO NOT COMBINE. THE WATER IN THE DROPLETS THUS BOILS ON SAID POWDER BED, WITH THE RESULT THAT THE TACKY SUBSTANCE IN THE DROPLETS ENROBES PARTILCES OF POWDER WHILE THE WATER EVAPORATES. THE ENROBED PARTICLES GRADUALLY SOLIDIFY INTO POROUS GRAINS.