We are continuing work on the very fragile, large drawings of the Hotel Ponce de Leon. As noted in the previous post on these drawings, we have already separated them into three separate sections (as they originally had been), removed the dirty cloth backing, cleaned the surface of the paper, reattached loose pieces, and backed them with a heat set tissue to keep the loose pieces intact and provide the paper with some support while they were being digitized. We have decided to remove the heat set tissue backing and back these drawings with Japanese paper.
To remove the backing, we place the drawing on a suction table. The suction holds the drawing down as we gently remove the heat set tissue backing by separating it from the drawing with a spatula and pulling it off in small sections. Since conservation materials are designed to be reversible, it comes off relatively easily.
Next, we make starch paste using wheat starch and distilled water, which will be used as the adhesive for attaching the Japanese paper to the drawing. The wheat starch and water are combined over heat until they form a thickened paste. (The Northeast Document Conservation Center has a very informative leaflet on their website on using adhesives to repair paper artifacts. It can be found here.)
After this cools, we apply a thin layer to the Japanese paper making sure we apply the paste in different directions. Japanese paper is prone to stretching and shrinking so applying the paste in different directions helps ensure that it will not stretch or shrink all in one direction once adhered to the drawing.
The Japanese paper is then laid on the back of the drawing while it is still on the suction table and is kept there until it dries.
So far we have completed this work on two thirds of one of the drawings. In these images, John Freund, the head of the conservation department, demonstrated this process which I was later able to perform under his supervision. I hope we will finish treatment on the last third of the drawing this week.