By paying close attention to an artwork's condition and response to treatment, conservation professionals better understand the lining process and when to apply it.
[1] The purpose of lining a painting is to mitigate or revert wear caused by agents of deterioration by strengthening or spreading the tensile load of the artwork's canvas.
[2] Attitudes in the conservation world at large have shifted towards minimal intervention and concerns have been raised about the reversibility of lining paintings.
The main reason for lining a painting today is to strengthen a torn or otherwise weakened canvas to stabilize its condition.
[3] The Canadian Conservation Institute lists ten agents of deterioration that play a role in damaging an object or work of art.
The decision to reline a piece of art may be made if any number of agents of deterioration have caused excessive damage over time.
When this type of damage occurs, the artwork may exhibit uneven expansion and contraction of pigment materials relative to their canvas backing due to their chemical compositions.
Afterwards it was to be laid picture side up, with the image covered by a sheet of paper coated in paste (generally of a beeswax or glue base).
[6] If the painting was in a state that did not necessitate an entirely new canvas, the conservator or restoration specialist would move on to the step of adhesive application.
By using a fine-toothed comb and pumice stone, the decayed canvas would be gently scraped away revealing the ground on which the image was painted.
[6] The new lining canvas was pressed down onto the back of the picture by hand; then the outer edges of the lining cloth were fastened to the table by means of a large number of tacks, and a piece of wood with a rounded edge was passed over the back of the cloth, to ensure perfect adhesion.
Fielding cautions that "the greatest care must be taken that the hand does not stop for an instant, or the mark of the iron will be so impressed on the painting, that nothing can obliterate it."
This problem was mitigated by the introduction in the 1950s of vacuum hot-table processes, designed for use with wax-resin adhesives, which exerted a more even pressure on the paint surface; however the longer periods of heating and high temperatures involved often led to other types of textural alteration.
The minimalist approach to the conservation of paintings involves mitigating structural changes in loose linings, backboard, and frame glazing.
Although experiments with synthetic fabrics have been carried out since the 1960s, linen cloths are still frequently used for lining because they maintain the aesthetics of traditional painting.
[2] Polyester sailcloth is favored specifically because it is stiff, resists degradation, and can withstand a greater tensile load than linen.
Although, initially, pure beeswax was used, mixtures incorporating resins such as dammar and mastic, or balsams such as Venice turpentine, were soon found preferable.
[10] During the 20th century, it came to be realised that the impregnation of the paint layer with wax could have deleterious effects, including darkening of the picture, especially where canvas or ground were exposed.
Beginning in the mid-nineteenth century, wax-resin lining was introduced in an effort to offer protection over a wider range of humidity.
Debates around the lining of paintings have been recorded as far back as the end of the 18th century, with outcry denouncing the Louvre and the National Gallery.
In the late 20th century, scholars such as Percival-Prescot suggested the use of nonlining alternatives signaling a transition in conservation approaches [11] One of the most important debates surrounding the lining of paintings discusses the process's necessity in the first place.
Modern changes to interventive policies in the 1970's and onwards have spurred conservation specialists to maintain works of art and their original materials when possible.
[7] In the climate of minimal intervention, there is a consensus that professionals focus on mitigative collection management by controlling environmental factors that lead to deterioration in the first place.
In a small survey conducted by Joyce Hill Stoner, ninety percent of conservators selected against relining an artwork with smaller scale interventions being the second most popular choice.
In the case of wax-resin adhesives, vacuum tables with temperature control functions are able to uniformly apply conditions of heat and pressure across the surface of an artwork, reducing the liability of damage in the hand-ironing process.
Unfortunately, these tables also render the artwork subject to high pressure and heat leading to a different type of textural change that is equally as disruptive.
[11] Even though BEVA 371 is one of the primary adhesive agents used today, it still has its own issues and there have been efforts to remedy the shortcomings of different lining materials.
The results of this experiment show promise for the use of polyeurethane as a lining material that resists damage from physical forces, however tests have not been conducted on its ability to expand and contract with environmental temperature changes.