Step #1 Making the Gypsum Biscuits:
8 parts – water
1 part – finest gypsum powder or Plaster of Paris by volume
· Sprinkle the gypsum into the water through a sieve, stir continuously for at least 30 minutes or until the gypsum no longer sets.
· Then stir this mix every 2 hours for that day and the following 2 days.
· Cover with a damp cloth and leave it so for a full month, stirring it at least twice every day.
· Take then a sieve large enough, place a cotton sheeting piece or muslin inside the sieve and pour the water and the gypsum and leave to drain all the water, squeezing with your hand gently until all the water has been poured off.
· Make small cakes or balls of gypsum using your hands and let these cakes to dry thoroughly.
Step #2 Making the Gesso Sottile:
· Have your Rabbit Skin Glue glue ready and warm, pour the cakes, one by one into the glue, and stir to mix them well, until you obtain a heavy double-cream consistency gesso.
· Apply this gesso warm with a brush over degreased and already sized MDF or Masonite panels. Brush on 8 coats, at right angles. When you first brush a coat, the surface shines, wait it to dry until it becomes dull and matt before brushing the following coat. A total absolute maximum of 12 coats can be applied.
· Leave the panel so prepared to dry completely until the following day or maybe for 2 days if necessary.
· Finish by polishing the gesso with garnet paper or a pad of damp linen cloth, using circular movements across the entire surface. This technique will produce a marble touch effect just enough absorbent for oils.
PLEASE NOTE: The initial measure you used to measure the volume of gypsum and water for the cakes must be the same volume measure you use to measure the Rabbit Skin Glue glue. The quantities for the full gesso, i.e. the cakes and the glue, are 2 parts of Gypsum Cakes to 1 part Rabbit Skin Glue Glue. So, suppose you use a ½ pint glass. Measure ½ pint glass of Rabbit Skin Glue granules by volume and 10 x ½ pint glass of cold water, soak the granules and make the glue following one of the recipes previously given. Therefore, in keeping with the same ratio, measure 8 x ½ pint glass of water and 1 x ½ pint glass of dry gypsum powder (as indicated for making the cakes: 8 parts of water to 1 part of gypsum, by volume). It is important to keep the same measurement ratio all along in order to obtain the desired heavy double-cream consistency. You may have noticed that this ancient recipe does not include any white pigment, so your ground will not have the solid white opaque color, typical of a more modern traditional gesso. This, however, is not a shortcoming, as you will have a half tone ground from the onset to work on, by tracing a design on and applying a translucent Imprimatura.