Anatomy of a Painting
Paintings conservators consider paintings as layered structures. Identification and characterization of all the component layers of a painting is the essence of the examination process. This analysis informs treatment possibilities and is critical to the work’s long-term preservation.
The primary support refers to the image-bearing surface (e.g. canvas, wood panel) but there may also be an auxiliary support which in turn supports or strengthens the primary support (e.g. stretcher, strainer, wood battens).
Stretcher or Strainer – the wood frame over which a painting on canvas is stretched and fastened through the foldover edge (margins), typically using tacks or staples. A strainer has fixed joins whereas the joins of a stretcher are designed to allow for expansion so that tension in the canvas may be increased.
Canvas – the textile support on which the image is painted; cotton “duck” canvas and plain weave linen canvas are most commonly used. Some artists paint on textiles that were not intended for artistic purposes. A variety of weave types, fabric weights, and fibre types (linen, cotton, etc.) are possible.
Unorthodox supports may be utilized by artists, often for economic reasons. The reverse of an early work by Alberta artist Alex Janvier, RCA is shown here before treatment. The primary support was a finely woven cotton textile glued over an auxiliary support of corrugated cardboard cut from a 1950’s “Wagon Wheels” box. The painting was restretched over a rigid, inert support, but the cardboard was retained for owner Jackie Bugera, Bearclaw Gallery, Edmonton
The keyed stretcher with mortise and tenon joins shown above is a common type. Two keys in each corner allow for independent movement of the stretcher bars; each key may be tapped to open the join slightly, tightening the canvas. Keying out of a stretcher is best undertaken by a conservator to ensure damage does not occur.
Size is a translucent substance intended to decrease absorption by the textile and increase bonding with the paint (or ground if present). Traditionally the size is a water-soluble, animal-based preparation such as rabbitskin glue. If present, the size is applied first, and may or may not be followed by the application of a priming layer.
Ground or Priming is an opaque, preparatory layer that may be applied to the primary support with or without size and is similar to the size layer in function. The ground also alters the visual qualities of the image, and may contribute texture, light reflection, and if tinted, underlying colour.
Paint – In its simplest form and definition, paint is pigment bound in a medium such as drying oil or acrylic resin. Paint manufacturers modify paints with additives such as fillers and driers, typically with the aim of providing more consistent drying and performance characteristics throughout their entire range of colours. Oil and acrylic are now the most common media utilized by painters, but many other medium types are available, and more than one medium may be employed (“mixed media”). Artists may add other substances to paint such as sand, wax, tar, glue, resins, manufactured mediums, or virtually any substance imaginable…..these additions may or may not be visible but can greatly alter the paint’s characteristics including solubility, durability and ageing properties.
Frequently the image is first drawn by the artist on the prepared support with a medium such as charcoal or graphite – this underdrawing may remain visible where uncovered by paint, or thinly painted/with translucent paint. Of course the design may be worked up in multiple layers of paint, sometimes over a protracted period.
Surface Coatings, Dirt and Accretions
A translucent substance such as dammar resin varnish may be applied over the paint to protect the surface and enhance the paint’s optical properties. Natural or synthetic resins may be used. Each resin type has distinct handling and performance characteristics that is affected by the varnish formulation. With ageing, some varnishes become brittle or yellow. Other kinds of surface coatings employed by artists past and present include wax, oil, industrial coatings, and proteinaceous substances.
Dirt may be trapped below a surface coating as well as accumulating on the topmost surface. Accretions such as accidental paint spatter and fly specks can damage the surface in addition to being unsightly.