Sachi Yanari-Rizzo, Curator of Prints & Drawings
When people think of a museum’s permanent collection, paintings comes to mind immediately. Collections care takes into consideration the inherent properties and needs of each medium or material. In a previous blog, we talked about how important the environment is; now, let’s look more closely at the physical structure of paintings and how environmental conditions impact their natural aging process.
What Is a Painting? The Support
First, what is a painting? A painting is made up of several parts—often a support, preparatory layers of size and ground, paint, and sometimes varnish. The support is the bottom structure that holds all the layers. It is most commonly wood panel or fabrics, like linen, cotton, or a synthetic; however, artists may use other materials for a support, such as copper, glass, cardboard, Masonite, or plaster, which is used in fresco. For example, in Urnscape (1993), pictured below, Ginny Ruffner painted small Impressionist landscapes on the surface of the ovoid glass disks.
Wood, the customary material used for a support, is an organic material and subject to decay. Despite this, remarkably, examples of paintings on wood, even from antiquity, have been preserved. The Fayum, or Roman Egypt mummy portrait paintings, date from the first through the third century A.D. and can be seen at the Metropolitan Museum of Art. Wood planks were the main support used in Europe from the Middle Ages through the Renaissance for painting religious icons and altarpieces, and are still used today. Oak was common in Northern Europe and poplar in Italy. Some wood panels have an additional support, known as a cradle. The cradle is made up of a grid of wooden bars on the back side.
Beginning in the 15th century, artists started painting on fabric, which largely replaced wood panel as the support of choice in Europe. Canvas was a lightweight solution as the scale of art increased and the market became wider and more international. In the photo set of Bellotto‘s painting below, you can see the weave on the back of the canvas.
To maintain a tight painting surface, the artist stretched the canvas over a structural foundation comprising wooden bars joined at the four corners. Wood bars may be added to provide structural support to large-scale pieces. A strainer has corners that are fixed and are not adjustable. Stretchers, however, are more adaptable since they are built with mortise and tenon corner joints. Narrow slots are cut into the wood stretcher bars near the corners. If the canvas is slack, thin triangular wedges, traditionally made of wood, can be tapped in (known as keying out, see photo set below) forcing the joint apart and thus making the canvas taut. Although keying out was often used as a conservation method for deformation of the canvas, it is no longer recommended once a ground and paint have been applied.
What Is a Painting? Preparatory Layers
Sizing (glue, starch, gelatin, or varnish) is applied to a wood panel or canvas to fill in the surface. It is necessary to apply a sizing especially if using oil paint as this thin layer seals the fibers of the canvas and acts as a barrier against the oil that could otherwise cause the fibers to degrade. An application of an opaque coating, known as a ground (primer or gesso), helps to give the artist an even surface to ensure good adhesion of the paint layers. Sometimes, though, artists will skip this step and paint on unprimed canvas.
What Is a Painting? Paint Layer
The paint layer is made up of pigments that give paint its color, plus a binder. Pigments can be made from inorganic materials (minerals, metals, and metallic salts) or organic materials that are made from carbon-based life forms (plants, animals, and synthetic dyes). Pigments are mixed with binders yielding distinctive visual and physical characteristics. Binders include linseed and walnut oils that are used for oil paints; egg yolk for tempera; beeswax for encaustic; and synthetic resins for acrylics. Certain pigments are light-sensitive, so paintings may be susceptible to fading, darkening, and discoloring.
By the early 1960s, artists used acrylic emulsion paints widely. They boasted a quick dry time and were less likely to fade or yellow. Application of acrylics directly to the unprimed canvas became popular in the mid-1950s through the mid-1970s, especially amongst Color Field painters Morris Louis, Kenneth Noland, Paul Reed, and Helen Frankenthaler. This became known as staining, since the paint soaks into the untreated canvas. Some areas of the work remained unpainted, leaving exposed raw fabric. Conservators in this case need to consider these works as both a textile and a painting.
What is a Painting? Varnish
Lastly, an artist might choose to brush on a thin transparent layer of varnish over the painted surface. Varnishes are natural or synthetic resins in organic solvents. They visually amplify the color saturation while protecting the paint layer from pollutants in the air. Although natural varnishes begin transparent, hard, and glossy, they can discolor and darken through the years. Acrylic paintings are usually unvarnished, which may make them more vulnerable to collecting dirt.
Care of Paintings
Prevention is key to avoiding physical and chemical damage. A frame is a valuable addition to the work, especially if it is original to the piece or made by the artist. Adding a nice quality frame can enhance the aesthetic experience while viewing the painting. It also offers a form of protection by adding some rigidity. The frame should be wide enough to avoid touching the actual surface of the painting while handling, and should extend beyond the surface of the work.
You may have noticed that we avoid hanging paintings above the vents in the gallery. Dirt, grime, and dust built up over time can obscure the image in the painting.
We typically cover the entire back of a painting on canvas with a rigid material like Coroplast, Gatorform, or Fome-Cor. This is screwed to the back of the stretcher or strainer, acting as a buffer against sudden changes in environmental conditions, blocking out dust and dirt, and reducing the vibrations caused when moving the painting. We hear horror stories about people at home who have stored works temporarily by stacking them against a wall. With no backboard, another work’s corner or edge can accidentally slip and dent, puncture, or tear the canvas.
Some collectors and museums choose to frame paintings in ultraviolet filtering glass that provides some protection from ultraviolet light, dirt, and dust. A spacer or inner frame liner is used so that the glass is not in direct contact with the painting’s surface. On the other hand, this will alter the viewing experience of the painting.
Using two points to hang is more stable, as the work is less likely to shift if bumped. If one hanging device should fail, there is still a back up to prevent the painting from falling. We prefer to install D rings onto the back of the frames as this type of hardware comes in various sizes rated for paintings of varying weights. To hang paintings, we prefer hooks that also accommodate a range of weights.
And what happens when paintings aren’t on view? Framed paintings are stored on movable wire screen racks on tracks that allow the racks to be compressed to save space. (You may have seen a similar system in a library). The heavy gauge wire screen allows us to hang anywhere on the vertical surface with metal S hooks. The racks are a compact solution that provide easy visibility and access. Works have permanent homes, so that they are easy to locate. Some storage solutions include racks that slide out instead.
An interesting challenge to storage in the collection is Gilport D XXX, which is composed of two trapezoid shaped pieces of unframed canvas. It was Paul Reed’s intention to experience his painting without a frame. Instead, the work is pinned to the wall with thumb tacks, leaving a visible gap in between the two panels. We re-use the same holes each time it is installed. While most framed paintings are stored vertically on a rack, Reed’s painting is treated like a textile and is stored on a tube that is covered with an acid free paper. It is rolled with the painted side out, to decrease the chance of the paint flaking, then covered again with an acid free paper and labeled; hung on a rack so there is no pressure on the painting from resting on a surface.
Paintings are vulnerable to bugs. Insects that are particularly problematic for paintings include carpet beetles and powder post beetles. Carpet beetles are attracted to the protein in sizing material on canvas. Evidence may include holes in the canvas, worm-like insects, or fuzzy carcasses. A tell-tale sign of past or current presence of a powder post beetle are small holes (about 2mm) in wooden materials. Be on the lookout for a substance of sawdust consistency known as frass, which might indicate that the infestation is active.
Excessive levels of light can lead to a build-up of heat. Therefore, small light fixtures placed in close proximity to the work may not be the best lighting solution at home. Since paintings are made up of layers of materials with different physical characteristics, dramatic fluctuations in temperature and humidity impacts these organic materials in different ways. The canvas or wood can absorb moisture and swell with higher humidity and contract when it is dry. Wood panels can warp and split. Fabrics can tighten in high humidity and grow slack in low humidity, a cycle that can result in ripples along the edges. Paint is not particularly flexible and may loosen its attachment to the layers underneath, putting it at risk of cracking and flaking as its support expands and contracts.
Calling in a Conservator
At this point, a painting conservator might be called in to do some consolidation work, where insecure paint areas are stabilized by using an adhesive. Inpainting is done when there are areas of paint loss. The conservation work might include removing layers of grime or a discolored varnish.
Besides using a variety of microscopes to examine the surface, there are many techniques involving light waves that painting conservators use to gain a better understanding of the construction and past touch-ups. Ultraviolet light is used to examine the surface layer, infrared light can help them understand what is just under the surface and paint layer, and X-rays go through the layers to provide information about the solid structure.
Despite its inherent fragility given all these variables and the disparate materials that make up a painting, it is extraordinary how well paintings are preserved today. Many artists received training as apprentices and through art academies that promoted techniques that were durable. In the 20th and 21st centuries artists have pioneered the use of untraditional materials, which will contribute to new challenges in preservation.
Come see Sachi in the Print & Drawing Study Center Tuesday-Friday, 11am-3pm, or by appointment.