This blog post is part of a series of observations about the London “Gels in Conservation” conference co-hosted by the Tate and IAP (International Academic Projects, Ltd). In mid-October, over the course of three days, some 41 authors presented research, techniques and ideas on gels in conservation. The talks were excellent, and I’ve focused on four that were notable for the wide range of materials treated and challenges faced. They ranged from coating/grime removal from a giant sequoia tree cross section, to dirt and varnish removal from Delacroix wall paintings, to removal of repairs from a fragile felt hat from a 18th century ship wreck, and an experiment comparing residues left behind by various gels on paper.
The first session of four, “Giant sequoia: an extraordinary case study involving Carbopol gel”, was presented by Lu Allington-Jones and was intriguing for several reasons: the object was enormous–5 meters (over 16 feet) in diameter. The size alone produced significant challenges, for which solvent gel was particularly suited. The scale meant that it would be treated in situ in full view of the public, thus potentially exposing patrons to chemical fumes; it would require large amounts of materials to treat; and it was at the top of an open staircase, meaning significant height came into play, as well. The giant sequoia cross-section had been on continual display since 1894, so it was incredibly dusty, had a darkened and cracking lacquer coating, and had a very friable bark around its perimeter. A material was needed that could safely remove the failed coatings and accumulated dust without penetrating the surface, harming the friable bark, or creating an unsafe environment for the conservators and patrons during treatment. Using a solvent gel had the advantage of keeping the solvents contained, reducing solvent vapor, and could act as a poultice to reduce grime and solubilize the failed coating. In addition, because gel ensures contact with the treated surface, it means that a lower concentration of solvent could be used as compared to a free liquid solvent. The gel was made 24 hours ahead in Ziploc baggies, the time allowed the gel to reach the needed smoothness and viscosity.
For application, the Ziploc bags were cut open at one end, the gel squeezed out and spread to 20 mm thick (about ¾”), then covered with plastic wrap to slow evaporation, giving the conservator about an hour of working time before the gel became too sticky and unworkable. Once the gel softened the coating, it was then removed trowel-like with a piece of cardboard, repeated, then cleared with industrial methylated spirits and wipes. A significant lesson learned about the gel was once it reached 73F or more, it became runny, causing the gel to slip off the vertical surfaces being treated, which didn’t allow enough working time to reduce the surface coating adequately. Once treated, the cross section was varnished with a protective layer of Laropal A81. The cross section looked amazing in the after images. I would encourage everyone to read the article in the post prints as it describes the details of challenges, decision making, and final outcomes.
This blog series is a result of receiving the FAIC Carolyn Horton grant to help me attend the conference. I would like to gratefully acknowledge the FAIC for helping make it possible for me to attend this important conference.