Conserving Watercolors: Misting to Stabilize Paint Layers

In preparation for the Museum’s current exhibition, Brushed With Light, conservators in the Paper Conservation Department examined over ninety watercolors. It was great to work on familiar works as well as those never examined or exhibited before. A common condition problem we observed during examination was the presence of unstable paint layers. Watercolors consist of pigments ground in gum arabic, a water soluble gum usually from the acacia plant, which holds or binds the pigment particles together and allows the color to be brushed onto a paper support. There are numerous causes for the paint to become unstable and lift away from the paper, including an insufficient amount or deterioration of the gum binder which can cause cracking and if left untreated, can result in paint loss. Some artists painted their images thickly, squeezing paint right out of a tube to create raised areas of paint called impasto. These areas are vulnerable to loss due to expansion and contraction of the paper and to a lack of adhesion to the paper. Some artists occasionally mixed additional gum into their paint, or as a glaze on top to add saturation to areas of flat color. With age these areas can become brittle and tend to crack and loosen.


In this photograph, I am consolidating lifting and powdery paint on the watercolor, The Samuel Fleet Homestead by Frances Flora Palmer, from the 1850s. The watercolor depicts a house which once stood at the corner of Fulton and Gold streets in Brooklyn and was reproduced in an 1884 publication, History of Kings County and Brooklyn by Stiles.


The piece was previously attached to a stretcher and in the image above you can see it was darkened in the central area where it was once exposed to light. It had been treated extensively in the past, but recent examination under magnification revealed areas of lifting paint where the artist used additional gum binder to enrich shadows in the trees and foreground, and to add dimension to the horses and some of the figures.


To consolidate, or re-adhere the loose pigment particles and flakes, I applied an adhesive using this ultrasonic mister. Most of the time consolidation is done with an adhesive introduced with a very small brush under the microscope under one paint flake at a time. The advantage of the mister is that the adhesive—in this case a photo-grade gelatin in ethanol and deionized water—is formed into minute particles which are smaller than the pigment particles. Because of their size they are easily absorbed into the pigment without changing the appearance of the paint layer and can be applied to a larger area at one time. This is an incredibly successful and useful technique for stabilizing powdery paint and small, light paint flakes as with this watercolor. In this case I am carrying out the treatment on a suction table which creates a downward pull to further enhance the absorption of the consolidant into the paper.

In my next post, we’ll go under the microscope to see the before and after effects of consolidation with an ultrasonic mister on another watercolor in the exhibition.