Four gel methods for each composition have been prepared: the colloidal gel method (CG), the gelatine
protected gel method (GE), the citrate method (CI) and the polymeric gel method (PG). Using a conventional
ceramic method, composition 3 has been prepared as reference in order to compare with the products of the ammonia water solution was dropped until gelation occurred at pH=5–6. This gel was aged at room temperature
in the open air and dried at 100 C. Then it was crushed and ground in an agate mortar