The Natural Aging Process of a Textile Support
When accessing a painting on a textile support there are several common types of damage to be aware of. Each of these problems stems from a separate cause. Textile supports were used traditionally in European paintings. The textiles themselves were made of flax, linen, hemp, cotton, and other synthetic materials. This method became popular in the 16th century and the prior tradition of using wooden supports faded out of style. By the 18th century textile supports constituted the principle support used in Europe and the United States.
Like all organic materials, textile supports are not exempt from the natural aging process. As the supports age they loose their elasticity and firmness and in most cases eventually cease to be able to function as a support for the paint layer. In the past a conservator would approach this problem with a blanket solution. Now, due to better training and modern inspection procedures and technical equipment this issue is now dealt with an ever-increasing sophisticated visual approach.
It is no longer sufficient for a conservator to apply general and unspecific solutions to paintings that each present their own difficulties and sensitivities. This turning point in the treatment of textiles is marked by, “The Conference on Lining Techniques,” that took place in Greenwich England in 1974. As a result of this conference a three-year moratorium on lining was put in place in order to allow time to help better understand its effects.
It is important to at least have a basic knowledge of the history of lining textile supports. This particular technique of lining can be traced back to the seventeenth century. However, it is not known where it was first practiced. Both France and Italy claim to have invented the procedure. The earliest evidence that has been found thus far points to Amsterdam in the form of an invoice made by a conservator in 1660.
Lining in its most basic, abridged definition, is attaching the original canvas of a painting to a new canvas. The first linings were done with paste, rye or wheat flower. However there are many different recipes some including molasses honey and various drying agents. A hot iron would then be applied. Very few documents remain describing the original hot wax lining technique. In a rare primary document a French dictionary describes the procedure, published in a 1757 edition. Despite this piece of evidence, many experts continue to believe the process of lining was invented in Amsterdam. Rembrandt’s, “Night Watchman,” was lined with hot wax around 1853. Using hot wax is known as, “The Dutch Method,” that gained wide acceptance in the 19th century. It was the hope that textile supports could be conserved in this way for eternity.
In the 1930s new methods were actively sought out to incorporate new materials and mechanical appliances. During this time it was common practice to use lead white oil paint to line a painting. While creating a very strong bond it also had the effect of drying something like cement. As the technology became available with the introduction of the electric iron, the hot table, invented in 1949, and then the invention of the low-pressure vacuum table in 1974 new methods developed and were incorporated into the lining process.
In the 1970’s synthetic adhesives replaced those used historically. These synthetic bonding agents eliminated three major risk factors for conservators: pressure, heat, and moisture. Synthetic resin with its low melting point made it no longer necessary to preheat the lining adhesive. This made the low heat-sealing method, and cold lining possible. These methods, unlike the ones historically used, achieve a great degree of reversibility. They also lessen penetration of the bonding agent into the textile layer and the paint layer.
In order to line a painting pressure must be exerted on the surface. For this reason linings can cause damage not only to the outside of the painting, but also from within the structure itself. Such damage is usually not perceptible, however, it will weaken the structure of the painting and may lead to further damage. Heat is also another hazard increasing the chemical reactions taking place inside the painting. Unfortunately, other very common causes of damage are due to vandalism and careless handling.
Aside from these factors, the most damage to textile supports are caused by negative properties of cellulose in the fibers. The properties of cellulose cause oxidation by absorbing atmospheric oxygen causing paintings to age. Oxidation is unstoppable. The cellulose in the fiber of the painting absorbs photochemical reactions and breaks down the fibers. Acids present in the atmosphere attack cellulose. This process is further exacerbated through contact with drying oils from the paint surface that, as it dries, absorbs large amounts of oxygen. Cellulose in the fiber possesses hygroscopic properties. This means that the fibers absorb moisture from the atmosphere and swell up becoming thicker and shorter. At the same time the canvas fibers also release moisture. In other words, a canvas does breathe. This loss of moisture causes the canvas to stretch and become slack. A loose canvas is subject to gravity and unchecked will progressively bulge down. This is one reason there are keys in a stretcher and why it is important to provide a solid and stable sub strait.
As the paint layer oxidizes the canvas looses its elasticity and becomes brittle. The fiber of the canvas will also react to the constant and substantial mechanical stress of the stretcher. Dust particles and other airborne pollutants settle on the back of the painting, in the gaps between the stretchers and in this way contribute to this aging process. Climate pockets may form from behind the canvas and the wall. This provides an ideal place for mildew to thrive. These climate pockets also give rise to the diffusion of water vapor through the textile support and painting layers. This causes serious craquelure. This is why as a conservator it is of the up most importance to put backing boards on all oil paintings.
The very properties of cellulose in the fiber provide a potential breeding ground for microorganisms. Under most circumstances the only effective step to safeguard against mold is to reduce the relative humidity in the environment surrounding the painting to 50 to 60 percent. Humidity at this level does not provide sufficient moisture to sustain fungal growth.
Damage is further caused from visible and invisible rays in the electromagnetic spectrum, notably, ultra violet rays. Last, but not least, the callous in the fiber and paint layer is affected by previous conservation or restoration treatments.
In considering the paint layer itself its important to have an understanding of the artist process of laying paint. Until the 19th century the paint layer of a painting mostly consisted of several color layers superimposed one layer upon the other. In this complex manner artist were able to achieve the most complex of color effects. Only rarely were the pigments mixed with each other, as is customary in modern paintings. They were mostly used in pure form and only lead white was added to make colors lighter.
Here are several things to consider.
1. The painting support
a. This is the textile support including the stretcher or strainer
2. The ground layer
3. The paint layer
4. The binding agents
5. The varnish layer
6. Previous restoration
c. Over paint
Let us further consider the issue of over painting. If the original painting is partially or completely covered with several layers of paint by a hand other then the artist, this condition is known as over painting. In past centuries paintings were often over painted in guise of being retouched. Some paintings can be considered over painted when the retouching extends beyond the boundaries of the defective area into the original painting. The term over paint may also be applied in the case of “beautification” in accordance with the contemporary taste of the time even if there is no defective area underneath.
When speaking with your conservator remember to understand these issues and understand that these 4 issues are addressed.
Choose not to line a painting unless it is absolutely necessary.
Choose to reweave a canvas when at all possible and choose not to patch.
Choose to in paint and not over paint any paint losses, or have a conservator remove over paint.
Be sure all materials used are easily reversible.
Make sure a backing board is securely attached to the verso.