Reports and write-ups on “Conservation of a canvas paintings” generally skip or very slightly mention the problems (and their treatment) at the back of a canvas painting. We need to understand that back represents the health of the canvas support on which the paint layer is resting. Dust/dirt has a tendency to collect on the back of paintings. It settles between the canvas and stretcher bars, and gets engrained in the exposed canvas.
In this write-up i will discuss how we might be able to treat some common problems at the back of a painting to avoid accelerated degradation of the painting. Here i would share the experience of treating the back of a painting in our conservation lab these days.
Following pictures would help understand the problems that need treatment to improve and increase the life of a painting:
From the pictures we can identify some basic problems in this particular canvas painting, for which we can create a methodology and start treating. We might find more problems or new more accumulated deteriorating agents while cleaning the back.
We started treating the back of this canvas painting from simple to more thorough and comprehensive cleaning procedures.
1. Removing the dust with dust attracting sponges, brushes and vacuum
The loose dust and accretions are easily removed with brushes. More deeper dirt is picked-p with dust attracting sponges and mini vacuum.
2. Treating the tide-lines with agarose gel
Tide lines are actually concentrated accumulation of various water-soluble components accumulated in the canvas because of spilled over water and its movement through capillary action.
Tide lines are the result of a chemical reaction when contaminated water reacts with soluble degradation products in canvas (or paper, in case of paper paintings) that has the ability to pull liquids either by wicking or capillary action through the material to the point where evaporation takes place leaving behind the contaminates and degradation products producing a line that disfigures the object and weakens it.
At room temperature, individual agarose pieces are applied to a portion of tideline and allowed to rest on the surface for some time. The agarose pieces imbibe the soluble components in the tide-line during contact with the surface of the canvas, by diffusion and capillary action. Slow acting agarose pieces not only pick up the acidic and damaging water soluble components of the tide-line but also hold moisture in check .
Most of the water soluble components of tideline are absorbed by the agarose gel, rest were diffused.
All the tidelines were carefully removed from the back of the canvas and it looked much better than before. There were still some stains and some diffused components left from the tide-lines.
3. Cleaning with pH adjusted water
The back was further cleaned with adjusted water and results were great.
Whatever processes we were doing at the back, we checked regularly if it is affecting the front. Some tests were also being conducted at the front in between the three cleaning processes of the back. It was interesting to note that as the back was cleaned, the complete painting (both from front and back) looked healthier and much more treatable.