The mechanical tensions the support undergoes over time generate cracks (craquelure) that form in all the layers of the painting (ground preparation, pictorial film, varnish). These tensions transform the surface into a series of islands that are separate from one another. In many cases, this phenomenon is very light: it does not create limits to the legibility of the work and it does not create particularly dangerous situations for the conservation of the work over time. In the case of drying cracks the phenomenon can be considered as a testimony to the life of the work in time and can almost be considered a testimony to its authenticity (“noble” craquelure).
A characteristic of ageing cracks is the tendency of the edges of the islands to curve up, creating a particular type of craquelure called “cupping” after the form that it takes. The edges curve upward gradually and are ever more noticeable, eventually detaching from the support.
This curvature of the edges of the craquelure can cause the complete detachment of the various islands from the support, and consequently the loss of material.
A situation that can lead to the loss of pictorial material can be due to the contraction of the support that brings about an overlapping of the pictorial film. This condition – frequently seen on canvas paintings and in particular works dating from the 1800’s – can occur when the of the canvas before it receives the ground preparation is inadequate. Just as important, are the type of fiber and the weave of the canvas.
nly in rare cases when the canvas is unusually thin, will it be the canvas that is deformed. This is seen on the back of the canvas and is evidenced by the wrinkling corresponding to the breakage lines of the craquelure.
Frequently, loss of adhesion can be found between the support and the overlying layers as a result of a loss in the cohesion of the ground preparation. This can be due to environmental factors or to materials used in the construction of the work (such as: the scarce amount of glue in the mixture). In this case, the flaking is localised in more or less vast areas of the work. Widespread detachment can occur due to incorrect construction procedures: the scarce adhesion of the preparatory layer with the support can in fact be due to the use of water repellent or non-absorbent materials.
The pictorial film can be compromised due to loss of cohesion processes that augment the porosity. This can be due to environmental conditions that are particularly humid, to the lack of protective films (varnish), to inadequate treatments, as well as the natural ageing processes.
Manfredi Faldi – Claudio Paolini
Estratto da: Artis (Art and Restoration Techniques Interactive Studio), Direzione scientifica: Manfredi Faldi, Claudio Paolini. Cd Rom realizzato da un gruppo di istituti di restauro europei, coordinati dall?Istituto per l?Arte e il Restauro Palazzo Spinelli, con il determinante contributo della Commissione Europea nell’ambito del programma d’azione INFO2000.
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