AIC’s 39th Annual Meeting – Joint Paintings/Research and Technical Studies Session, June 3, “Developing Cleaning Systems for Water Sensitive Paints by Adjusting pH and Conductivity” by Tiarna Doherty

As a fitting end to a conference full of great talks, Tiarna Doherty, from the J. Paul Getty Museum, wrapped up the final session of the joint PSG/RATS session at the annual meeting on Friday evening with an incredible talk about new developments in cleaning water-sensitive paintings. The project was a collaboration between herself and two others, Chris Stavroudis, conservator in private practice, and Jennifer Hickey, Graduate Intern at the Metropolitan Museum of Art, that aims to develop a methodological approach to cleaning water sensitive works by measuring the pH and conductivity levels of the surface of the artwork and cleaning solutions in use.

Doherty began her presentation by introducing us to the Modular Cleaning Program (MCP), a database system that has been developed to assist conservators in their approach to cleaning artworks. The MCP performs valuable computations which assist the conservator in creating cleaning solutions that take into consideration, pH, ionic strength, HLB, and the functions of surfactants, buffers, and chelating agents, within aqueous cleaning solutions. Using MCP workshops given by herself and Stavroudis as an example, Doherty highlighted how practical experience with the MCP has helped them to understand how paints interact with cleaning systems, and thus aided in their current research.

She continued by concisely explaining why they focused on pH and conductivity. First, recognizing that the pH of something as simple as water may vary widely, Doherty notes that even exposing de-ionized to air over a long period of time eventually causes the pH to lower. Likewise, carbonated water also has a low pH, but since an acrylic paint film swells at a pH of 7 and higher, the use of carbonated water has been shown to successfully clean some water sensitive acrylic artworks. Doherty finished her introduction on pH with a brief explanation of buffers and the use of acetic acid and ammonium hydroxide to adjust the pH of water for cleaning, noting that both of these components of the solution will evaporate over time without leaving a residue on the surface of the artwork.

Next, Doherty continued her talk by segueing into an introduction on conductivity. Conductivity, the ability of a solution to transfer (conduct) electric current, was recently explored as a means to evaluate the surface of an artwork during cleaning and to create/develop useful cleaning systems. In a simple manner, the conductivity of a painting’s surface can be measured by placing a small drop of water on the surface of the painting, and then transferring it to a conductivity meter after a short period of time. Doherty reported that recent research in the field has concluded that there is less swelling of a water sensitive paint surface when it is cleaned with a solution that has a of pH of 6 or lower and a conductivity of 6000 micro-Siemens.

The talk continued with two in-depth cleaning case studies on an oil painting and an acrylic painting, which were both painted in the 1960’s, and had proven to be sensitive to water. Using solutions with adjusted pH, various conductivity levels, and the addition of materials such as chelators, surfactants, and even an emulsion system containing a proprietary material called Velvasil®, Doherty’s team tested and successfully developed systems for cleaning each of the two artworks (which, to ensure accuracy of content, I will point you in the direction of the post-prints for the details of).

As Doherty concluded her talk, I couldn’t help but be a little excited about possible implications of this and future research on these topics. This talk not only raised many interesting considerations about the cleaning of paintings, but, it also revealed the practical application of a new a tool set for conservators who face the challenge of water-sensitive paintings.

Bravo Tiarna (and team), I look forward to hearing more as this project progresses.