Cleaning Research for 18th century Unvarnished Water-sensitive Matte Tempera Paint

Abstract: This master thesis studies various cleaning techniques used to conserve the unvarnished matte tempera painted surfaces of the Per Stålhammar funeral coat of arms for the Kalmar Läns museum (KLM 014946). The polychrome sculpture is dated from 1701 and has never been conserved before. This led to a critical condition, and the object required careful and immediate preservation. During the conservation process, the areas painted with blue pigment smalt were noticed to be more fragile and sensitive to cleaning strategies applied to other areas of the polychrome sculpture. Subsequently, the research identified the paint, ground layer, and surface material composition of this problematic area. After identifying the materials components, the artificial mockups were created to use as a surface to test cleaning methods. The selection of cleaning materials was derived from the previous research, proposing dry-cleaning methods and hydrogels, which proved suitable for water-sensitive paints. The examination of cleaning methods was tested with Microscopes, Scanning Electron Microscopy (SEM), and an Artificial aging chamber. The overall goal was two-fold. First, contribute to the knowledge gap in the cleaning research performed on unvarnished matte tempera polychrome sculptures. And second, to find a method that will not affect the original surface and perform a safe and efficient cleaning without creating watermarks, have a pigment pick–up issue, or leave residues on the substrate. The investigation showed that the dry-cleaning method and use of hydrogels could work together and target different tasks. Among the dry-cleaning materials, the best result was performed by Yellow fibecloth and Evolon-CR©. The novel hydrogels by Nanorestore Gel ®, the type HWR, and MWR were selected as safe materials when examining the wet cleaning methods. Those hydrogels suggest a controlled removal with a low – risk for the painting surface. This research will alleviate the future conservation decision–making process on art objects with similar matte tempera paint surface conditions.