Conservation of canvas easel paintings.
- Clare Finn
Canvas paintings have been restored for centuries and some paintings may have undergone conservation many times. Work may have been carried out to repair mechanical damage such as tears or distortions in the canvas, to reattach flaking paint, and to address materials the original artist used that may have deteriorated. There are also aesthetic treatments such as removing dirt or yellowed varnish from the painted surface. As a consequence of the aging of the original materials, no artwork will look the same as when it was first painted after some time has passed. Even contemporary paintings may be made with materials that age within an artist’s lifetime, and consequently need conservation treatment.
1. Causes of deterioration.
In the days before heating could easily be controlled, rooms were heated by open fires. Light was provided by candles or torches made from oil-soaked rags. Thus the natural processes of aging to which paintings were subjected were exacerbated by seasonal and diurnal changes in temperature and humidity, as well as the soot and fumes given off by these fires. Paintings of all media can be affected by air-borne surface dirt settling on their surfaces, but unvarnished surfaces are affected more directly than are varnished ones. Acrylic paintings are affected particularly adversely as dirt does not always remain on their surfaces but can be drawn into the paint layer. Varnishing is not always the solution. Some modern media cannot be varnished and varnish itself can discolor with age, changing the look of the paint it covers, whether it is a traditional oil or modern paint. In fact, some artists never intended their work to be varnished. Aged canvases become brittle and no longer perform their primary function of supporting the paint. Contemporary works also suffer from uncontrolled, fluctuating enviromental conditions. Mishandling can result in bumps and scratches.
2. Approaches to conservation.
The way paintings are repaired today, as distinct from the past, differs not just in the modern materials available with which the work is carried out but in the overall approach to the work. Not everyone who repaired paintings in the past was a restorer. Parry Walton, who was the first to treat Rubens’s paintings in the Banqueting House in Whitehall in 1688, was listed as a restorer, but Giovanni Battista Cipriani, who treated them in the 1770s, was not. He was a painter, designer, and engraver, and this was reflected in his treatment of the paintings. He would be accused of having “repainted [the canvases] wholesale.” Traditionally, the work of a restorer was seen as a craft; only from the late 19th century did conservation become recognized as a profession. As a consequence, there are few records of early restorations, although evidence may be found by examining paintings themselves. There are exceptions to this dearth of surviving records. For example, some documents for treatments carried out on the Rubens paintings in the Banqueting House survive and among them is Walton’s financial account for materials and labor for their restoration. It lists cloth for lining, nails, colors, “oyle” varnish, and also priming, paste, and “glew.” The “glew” was probably animal-skin glue also used in carpentry. Paste may have been flour and water. Both become brittle with time and make excellent food for mold, insects, and rodents if they become damp. The “oyle” was likely linseed, though it may have been poppy or walnut. All these materials have been used by artists in the creation of paintings. Today one criterion for choosing materials for remedial repairs is to select media that will not be confused with those that artists used originally. Other criteria are that both treatments and the materials used in repairs should be meticulously recorded and be reversible as much as possible. The challenge for modern conservators is to stabilize both Old Master and modern works of art with a full understanding of their past alterations and an informed assessment of their future needs. This is not a job for amateurs but requires specialist training to understand the many issues involved and avoid just as many pitfalls.
3. The artists’ materials.
The manufacture of paint has changed hugely over time, and having a thorough and detailed understanding of their evolution is key for any conservator. Traditionally, paints were hand-ground, but machine-ground paints with smaller particles and different handling qualities were introduced in the 19th century and new synthetic pigments were also introduced at this time. While traditional pigments were not immune to change, a noticeable number of newer 19th-century ones were unstable, changing color and fading in light. Other colors have been affected because of pollutants in the atmosphere.
The early 20th century saw the introduction of synthetic media—alkyds, acrylic, and polyvinyl acetates—that dry more rapidly than oil paint and age differently. These modern paints contain additives that give the paints consistent drying times and flowing qualities but may lead to instability. These new materials have necessitated some radical changes in approaches to the remedial treatment of contemporary pantings.
4. Structural treatment.
Linen and cotton canvas supports weaken naturally as they age, and lining, which involves gluing a new canvas over the back of the original one, is the process by which a brittle or torn canvas can be strengthened. This provides structural support to the paint without removing the weakened old, original canvas. In time, as the lining canvas becomes weakened, the process is repeated and the painting is then relined. The glue used for linings in the past was generally animal glue, flour and water paste, or a combination of the two. The canvases were pressed together with heavy, hot irons. On occasion those irons would be so hot they burnt and blistered the paint, flattening the brushwork, crushing or melting the paint.
By the 1970s, wax-resin replaced animal glue and flour pastes as lining adhesives and pressured hot-vacuum tables were introduced. Wax infused into a painting made it resistant to mold and humidity when pictures were hung in damp, unheated, or overheated rooms. However, it began to be noticed that wax darkened canvases, altering the paintings’ colors, and did not stick particularly well to the surfaces of the painting. In addition, the use of vacuum tables was not suitable for all paintings. Synthetic fabrics and glues, subsequently introduced, offer more stable alternatives to natural linens, cottons, and animal skin glues. A wide range of methods and adhesives are now available and are chosen to suit the individual requirements of each painting. The glues and resins used today can be used more flexibly than those used in the past; they do not discolor and can be applied in various viscosities, which allow them as needed either to adhere loose paint from behind or not even penetrate the canvas.
If an original canvas is not too aged and brittle, then strip lining, which involves attaching strips of new canvas to the edges of an original canvas, is also an option. This technique can sometimes delay the need for a full lining. A loose lining can be stretched, though not glued, under the original canvas. This buffers and cushions a painting and is also especially suggested if a painting has to travel a great deal. Tears can be treated with a traditional patch, feathered at the edges, or with a thread-to-thread method which involves gluing each thread together under a microscope.
5. Aesthetic treatments.
Cleaning may include the removal of surface dust and deposits as well as layers of discolored varnishes. There are two basic approaches to cleaning: one is that discolored surface layers should be removed, another approach is that they should only be thinned and thus preserve a “patina.” Patinas are the changes to a surface over time and are often thought to be aesthetically appealing. “Old Master Glow” varnishes that were popular in the 19th century were intentionally darkened, often to the color of molasses. The removal of any of these layers using appropriatly tested solvents and reagents should be done only by well-trained professional conservators.
There are different approaches to treating areas of lost paint. Some reintegrations of losses are done through visible retouching, meaning that the losses remain evident. This can be achieved either by toning down losses in an even, uniform color or in a way so they are only apparent when the painting is viewed up close. Other approaches are to totally integrate the areas of loss so they are not evident at all. In both cases, the modern retouching is only applied in the areas of loss unlike the past when restorations often covered orginal surfaces.
The aging processes that paintings undergo is being studied and researched in an ongoing basis. Materials and techniques are chosen and are being further developed specifically for their long-term stability, reversibility, and resistance to discoloring. Above all the goal is that the original artists’ work and not that of the conservator should be the most prominent.
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