Summary of Technical Findings
Analysis of microscopic paint samples from the Hogarth portraits of William James and Elizabeth James provided a wealth of information to conservators. Cross-sectional views showing the layered structure of the paint samples gave conservators insight into the artist's technique and the various surface coatings applied over the years. It also confirmed the presence of a non-original pigmented varnish layer applied in a past restoration. This information was critical in gauging how far to take the cleaning treatment.
Cross-section analysis also identified an early coating material found in direct contact with the upper paint surface and now believed to be a contributing factor in the formation of micro-cissing. In addition to visible and UV light microscopy, the complementary methods of SEM-EDS and FTIR mapping helped confirm that the implicated coating is indeed protein-based and that aggregates of what is likely lead- and potassium-based metal soaps have formed on the underside of this coating. This evidence led the Museum's conservators to theorize that shortly after completion the paintings were coated with a temporary protein-based varnish such as egg glair or skim milk, which when applied to paint rich in lead driers and potassium-based soap, the combined effect likely caused the unique beaded appearance in the paint surface known as micro-cissing.Next: Ongoing Research