This drawing recently came to the paper lab to have some old paper remnants removed. The drawing is on the back of a letter, and some of the writing was obscured. A window mat had been glued to the edges of the sheet, and the paper fibers left behind after most of the mat had been removed are evidence that it was a wood pulp mat with a white facing paper. The stains around the image formed as a result of the acids in the window mat migrating to the drawing paper. Over what was probably years of light exposure while being displayed, the paper darkened where the concentration of acids was highest. The mat was attached with thick starch paste that formed a barrier between the acidic mat and the drawing and locally prevented degradation and discoloration of the paper.
The mat board and facing paper were thinned with a scalpel to reveal the paste. Paste was first thinned by softening it with poultices of fresh wheat starch paste and lifting it off with a scalpel. Remaining paste was brushed with enzymes to break the starch into smaller sugar molecules that could be more easily removed from the paper. Finally, the enzymes were rinsed from the paper. The application of water had to be controlled to ensure that none of the ink was lost during washing. Although the stains remain, the entire letter from Robert Blum to his friend William Merritt Chase can now be read.