What is it you have when you own a painting? What, inherent in the materials and construction of your painting could go wrong? Your painting, in all probability is painted on one of the following surfaces: canvas, card, paper, artistboard, wood, Masonite, metal, etc (See Figure 1). In preparation for the paint, a primer or gesso will cover the surface. The paint itself which is pigment in oil or acrylic medium is then applied on top of the gesso and this is followed, after the painting has dried, by a coat of varnish, not all paintings however, are varnished.
We will start our explanation of conservation with the top layer, the varnish, and work our way down. A natural resin varnish will yellow, sometimes even turn to a deep amber (See Figure 2). Very fine lines may appear as the varnish cracks due to the expansion and contraction of the canvas or the panel below. A synthetic varnish will start to grey and become translucent or cloudy, it may also crack, though generally it is more flexible than its natural counterpart. All of this, of course, is detrimental to the visual effect of the painting. But, if you prefer your blues green, your reds orange, and your whites yellow then by all means don’t remove the varnish.
Why does a painting even have a varnish if it discolors and its removal if done improperly, can be damaging to the paint surface? Simply put, oil paint looks better with a full gloss, as the quality of oil paint is naturally glossy. It has an oiliness or wetness about it when first applied, though this will dull overtime, which is when a coat of varnish is necessary to retrieve the optimum richness of color and the subtleties of glazing. Oil paint has a profundity when wet that it loses when dry. However, as we have mentioned, not all paintings are varnished. Acrylic paint has become commonplace, making use of varnish increasingly infrequent and a taste for a dry surface on oils, which became popular in the early twentieth century led to a “matte varnish”, which is intended to dull the surface ostensibly to achieve the appearance of an unvarnished surface, often unsuccessfully. Because of the difficulty in removing this type of varnish, it is best in my opinion to have no varnish at all and to let the painting be dull naturally; the surface can still be cleaned gently and successfully.
A conservator uses specific solvents to dissolve the different varnishes taking great care not to remove any paint. (See figure 3) Removing discolored varnish should provide an accurate perception of the painting when it was painted. The removal process requires knowledge of how the artist may have compensated for the aging of their materials. For instance, some artists would paint flesh pinker, to compensate for the varnish yellowing. Knowledge of an artist’s technique with oil paints is important vis–à–vis the amount of varnish or medium used with the pigments as they may be soluble in the solvents that were intended only to dissolve the varnish.
Next to be considered is the paint surface itself. Most of time’s attrition is left unanswered. Oil paint will become transparent, darken or fade according to the pigment and the amount of intensity and time of sunlight on its surface. The effects of moisture can cause the paint to crack or cup in a tent-like form, loosening the paint from its ground often resulting in flaking and loss, (See figure 4) or poor technique by the artist in surface preparation, paint and medium application, or use of poor quality materials, which can separate and crack, these conditions can be remedied with consolidation and inpainting. Consolidation is the process of gluing the paint back onto the gesso or support and realigning the surface to a flat plane. This is unfortunately too complicated a process to explain in these brief notes, but it can be executed either from the front or when possible from the reverse of the painting. This will achieve the effect of making the paint stable on its support and prevent further loss. At this point a coat of varnish, known as an isolating varnish, is either brushed or sprayed onto the picture. The oil painting is now in what we call its “actual state” that is, not restored but conserved.
Ares of missing paint are then filled with a gesso or acrylic resin, which will fill deep cracks or losses. (See figure 5). It is important that none of the original surrounding paint should be covered by fill. Then when perfectly level and textured, to imitate the brush strokes, the paint used for “inpaint’, which is a fast drying acrylic pigment in a ketone resin, is carefully applied to the areas of loss and the colour and gloss are matched to the original paint to make the match undetectable. One or more final varnish applications are applied before the work is completed to unify the surface.
And now to the third component of a painting, its support and secondary support. That is, the material it is painted on and what supports that material. Although I have left this until last to discuss it is actually the first stage to be approached. Before we can work on a painting we must ensure that the back is sound. Wood panels must be free of woodworm (See figure 6). and supported enough to prevent warping or cracking Canvas must have strong tacking edges, which are the edges that wrap around the stretcher bars. Stretcher bars must be straight and be keyed out to the correct tension. If the canvas has a rip, puncture, or has been damaged by fire or water, a second canvas may need to be glued (adhered?) to the original for strength. This is known as a lining canvas.
If you own a painting look at the back of the painting, make sure if it is a canvas on a stretcher it has all of its keys (the triangular wedges at the four corners) (See figure 7), and make sure it has a foamcore backing (paper is not enough). This backing serves two purposes, it helps prevent the canvas being pierced from the reverse, and it reduces the adverse effects that the large fluctuations in humidity can have on a painting, caused by the rise and fall of temperatures here in New England.
It is advised not hang a painting in direct sunlight, not to have it on an exterior wall, or over a fireplace. If you are storing a painting, the basement is not a good idea, nor is the barn. Remember, a painting is made up of three or four mutable layers upon an unsound support. It needs monitoring and care if is to be enjoyed by future generations. (See figure 8)