Now that we have cleaned the back of the canvas we can look at surface cleaning the front of the painting. This is a separate procedure from the removal of varnish and overpaints and is completed first because surface dirt is the first layer encountered. The reason we remove the dirt layer on paintings is because it considerably alters the colour and tone of original paint, can obscure image detail and significantly alter the surface gloss, clarity and hue of surface coatings.
When we carry out our testing, we apply the cleaning solutions with small cotton swabs in a rolling motion over the paint surface. We test inconspicuous areas first, starting with light colours and then progress to all the main paint colours. We keep and label the test swabs for comparison. We often have to reassess our cleaning strategy because the solubility of dirt and paint can change across the surface of the painting requiring the use of different materials and concentrations of solutions. The most common surface cleaning agents are aqueous in nature – meaning they are water-based. We can modify and control the properties of the water by adding pH buffers and ionic buffers and by adding chelating agents, surfactants, enzymes and gelling agents.
Last year I was able to attend a course in Melbourne about the cleaning of paintings using the Modular Cleaning Program. This is a database system and an approach for cleaning paintings that has been developed to help conservators use established theory and materials in a way which makes the complicated chemistry of cleaning more accessible. Basically, the computer program is better at working with piles of numbers than us! It saves us time by working out the complicated stuff, like ionic equilibria, which requires pages of calculations and is really boring and not to mention, tough!
Through our testing and the help of the Modular Cleaning Program, we arrived at a solution containing a mixture of enzymes which we will use to safely and effectively surface clean Poedua. The next blog post will talk about the surface cleaning process now that we have found our cleaning agent and will include some nice images of the cleaning in progress.