Conservation of Devout Men Taking the Body of Saint Stephen, dated 1776, by Benjamin West (American, 1738–1820):
February 2015, Surface cleaning
After thorough examination of the painting, conservators have formulated a treatment plan and conservation work has begun. Research into Benjamin West’s materials and techniques, known as the technical examination, is ongoing and updates will be posted regularly.
The first phase of the conservation treatment involves surface cleaning to remove the dust and grime that have accumulated on the surface of the painting. Just as dust settles on any undisturbed surface, dust also builds up on the surface of paintings. In addition to dust, other environmental pollutants, such as soot, had formed a distinct layer of grime on the altarpiece.
Surface grime can harm delicate artworks, serving as a basis for the formation of mold, attracting insects, and causing chemical deterioration of the underlying layer. In addition, thick surface grime can shift the overall tonality of a painting, making it appear darker or yellowed. It can also make a painting hazy or difficult to read as the grime scatters light off the surface of the painting.
A thick layer of grime can also impede an even reduction of the varnish layer, and so conservators will often remove grime in a separate step during the treatment process. This process of "unpacking" the surface allows for a much more nuanced treatment, particularly as the solubility of the grime tends to be different from the solubility of layers of varnish and overpaint.
To remove the surface grime on Benjamin West’s altarpiece, conservators use a water-based, or aqueous, cleaning system expressly formulated for this particular painting. The water is adjusted to a specific pH and a very small amount of a water-soluble chelator is added. The chelator only works at specific pH levels and binds selectively to ions in the grime layer, making cleaning more efficient. The surface is then cleared with pH-adjusted water to remove any residues. The detail below shows cleaning in progress; the left half has been cleaned of grime.
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It takes four weeks to completely clean the altarpiece, with conservators carefully applying small cotton swabs dampened with the cleaning solutions to the surface. Below is a detail of the surface cleaning of Stephen’s torso. The grime is dark gray, almost black, in appearance. At the bottom right, the gray discoloration of the uncleaned area is visible.
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In the coming months, conservation treatment will continue with gradual reduction of the yellowed varnish and the overpaint.