Painting with Distemper, Part 1
How do you accurately restore a wall paint that has been missing for over 170 years? This is a question that frequently confronts Monticello’s Restoration Department. Most recently it was the focus of an investigation in the second floor bedroom that Jefferson called the “North Octagon Room.” At the start of the project, the walls in the room were covered with off white paint and no written record of what the room looked like in Jefferson’s time survived. However, Monticello’s Robert H. Smith Director of Restoration Bob Self knew that Jefferson’s original wall color likely survived underneath the later paints. To find out, Self took small samples from the wall and sent them to Dr. Susan Buck, a paint analyst and conservator who specializes in historic architectural finishes.
Monticello has long benefited from paint analysis; many rooms in the house feature historically accurate colors based on microscopic analysis of paint samples. The first attempt to record the house’s paint history using this technique started in 1977 when paint analyst Frank Welsh sampled each of Monticello’s rooms. Guided by Welsh’s report, many of the rooms on the first floor were repainted to reflect his findings, but the second floor spaces were left unrestored because they were being used for offices. However, all employees were recently relocated from the second floor and so the walls in the North Octagon Room can now finally to be restored to their Jefferson-era appearance.
While the paints in North Octagon room were analyzed in 1977, Susan Buck was asked to resample the space because the science of paint analysis has advanced dramatically over the past 35 years. In this case Buck’s findings revealed that the first paint layer found on top of the plaster was a distemper paint. Distempers are ancient paints made from water, ground chalk, hide glue, and, if a color other than white is desired, pigments such as ocher and lamp black. Inexpensive and easy to produce, these paints were used for millennia in many different parts of the world and were commonly used in the United States until the 20th century. Besides being cheap, distempers were also popular because they could be applied over newly plastered walls and ceilings. Linseed oil-based paints were not used on fresh plaster because traditional lime-based plaster is very alkaline when first applied (it has a high pH) and so it breaks down the oil in the paint. Similarly, fresh plaster can also cause wallpaper to turn brown and disintegrate. Therefore distempers, along with lime-based whitewashes, were virtually the only paints used on newly plastered walls in Jefferson’s time. Earlier paint investigations have also revealed that Jefferson clearly liked distempers and used them for other rooms at Monticello, including bedrooms, stairwells, and the Dome Room.
In addition to identifying the type of paint used in the North Octagon, Susan Buck was also able to identify its color using two tools. First, multiple readings were taken from the samples using a specialized digital color measuring instrument called a Chroma Meter. This information provided Buck with a baseline color that she then checked with a second, and decidedly lower tech, instrument – her eyes. After fine tuning the color specification she recorded her results using both the Munsell system (a universal color reference system often used in architectural preservation and restoration projects) and the CIE L*a*b* standard (another widely used color measuring system). She ultimately determined that the North Octagon room was painted a light bluish-grey color soon after it was plastered.
The next challenge, which will be detailed in a future blog post, was to develop and apply a historically accurate distemper paint using the color sample and pigment identification provided by Buck.