The process of conservation is as much about analysis as it is about correcting problems which have developed over the years as art ages. It would be nice if once the artist had completed work nothing would happen to shorten its life. Unfortunately, everything ages even if no external trauma happens. That ageing of materials is one of the primary reasons steps must be taken in a timely fashion to prevent accelerated deterioration. It is a little like old cheese. Waiting does not improve it and, in the case of art, it does not heal itself with time.
We have all seen the results of inattention to the stability of art. First, little cracks develop in the paint layer. These are usually due to the subtle and sometimes not so subtle expansion and contraction of a surface on which the paint was applied. For our purposes, lets focus on paintings, since we are treating a mural which is a painting on canvas applied to a wall.
Over time, the absorbent materials and those which are susceptible to change in behavior based on moisture content affect the stability of a painting. Canvas dries out, adhesives loose their sticky properties and paint shrinks as the solvents in it evaporate. The evidence of this is the branched net like pattern of small cracks which develop in the paint layer. As the interval between the cracks develops it permits more drying and loss of attachment. Eventually, depending on the ambient temperature and humidity, paint flakes away and is lost. All of this happens under merely normal conditions. If we add a stream of water, whether from behind or flowing down the surface, the losses happen at an accelerated rate. What we loose is the original paint and the design integrity. That loss translates into a loss of value. Clearly, stopping the loss preserves value. More importantly, it allows the progress of time to increase the value and rarity of a panting.
With this as a background lets move on to the specifics of the mural restoration in the next post.