About a week ago, I started to saturate some plaster of Paris to make gesso sottile. This is the second layer of gesso that Cennino Cennini recommends for the outside of a helm crest. In an earlier post I explored the chemical composition of gesso. Gesso sottile is a super hydrated version of plain plaster of Paris. By soaking the plaster, you are allowing it to take on more H2O (water), giving it the desirable property of a slower drying time. This means we will be able to add the final sculpting touches with more care.
Since this is the first time I have used plaster in this way, to sculpt rather than to make moulded objects, it is all a learning experience. I have no idea how well the plaster will stick to the leather, or how well the second layer of plaster will stick to the first, or how the paint will need to be applied. It will also be the first time I have made pigment based medieval paints. There will have to be some test pieces very soon...
Cennini suggests leaving your plaster to soak for 30 days, changing the water to ensure it remains clean. Other sources say this method is inexact - but it is the best evidence I have, closest to my chosen time period, so I have tried this method first. We can always try something else.
To make gesso sottile, I fill a bucket with water and poured plaster in. It is always recommended that you add plaster to water, not water to plaster. When making a gravy or sauce, this produces lumps but for plaster it works well. I mixed it gently and continued to add plaster until it was not absorbed immediately. I covered the bucket with another tub to stop rain, cats, frogs and leaves getting in. Now, we wait.
