Tempera - mortars

Egg tempera needs a durable , but delicately prepared gesso ground.
It was mainly painted with it on wood covered with rare canvas to protect the paint layer from cracks and give better adhesion to the gesso. The binder for the mortar was animal glue, less often vegetable glue (clay).
Sometimes an emulsion of glue and oil was used in the last layers of mortar to give the mortar more strength.

Priming the board

According to Cennini, the process of priming a plank was as follows:
A solution of parchment (leather) glue was prepared at such a concentration that it glued the fingers together slightly.
Then it was poured into some vessel (filling it halfway).
The solution was diluted with water (1/3 of the volume).
With the glue thus diluted, the boards were hot glued. After drying, this operation was repeated two more times (drying each time), but already with a stronger solution (closer to the bottom).
After the wood was glued, the old canvas was pasted over it (over the entire surface or only at the joints).
The canvas was dried for two days. After drying, the surface was scraped with a knife, removing any roughness.