It is a protein substance that is a member of the group of adhesives of animal origin. It is obtained from skimmed milk, and has optimum adhesive properties. It has been widely used since antiquity in the preparation of supports, imprimaturas and tempera colours. Its success is tied to its insolubility in water that renders it barely sensitive to humidity, compensating in part for its defect; that is, it is less elastic than animal glue. In addition, both its solubility and take occur in cold surroundings. Indications for its fabrication are found in various medieval recipe books and in the writings of Theophilus (12th Century) and Cennino Cennini (end of the 14th Century) who speaks of "slaked lime and cheese glue" making reference to the coagulation of calcium, surely one of the most known and used glues of antiquity.