Collectors should build a basic vocabulary regarding the art of painting:
Support: the physical structure on which the painting is executed (i.e. wooden panel, stone, canvas, paper, etc.). If canvas was used, a second layer, or lining, may be affixed to the back to later add physical support.
Preparatory Layers: in the case of a painting on canvas, a product made of gelatin or glue – known as a size – is used to influence the fabric’s absorbency. A primer made from a mixture of plaster or chalk and water prepares the support to hold the paint. A final white basecoat layer of gesso is often applied before painting begins.
Tempera: best represented in the luminous paintings of the 14th and 15th centuries, the pigment is mixed with water and egg.
Watercolor: made of finely ground pigment bound with gum arabic or glue, its application can appear both transparent and opaque. The most common opaque watercolor material is gouache.
Oil paint: first widely adopted by 16th-century artists for its transparency, ease of manipulation, and rich colors. It can produce an incredibly smooth surface but can also be mixed with sand and other coarse materials to create texture. Oil paintings can take days, months, or even years to dry depending on the thickness of the paint as well as its chemical makeup.
Acrylic paint: introduced in the 1950s, acrylics were quickly embraced for their ability to look as matte as gouache or as translucent as oil paint. They are bound with a synthetic acrylic polymer emulsion.
Brushes: several brushes of a different shape, size, and stiffness can be used to create a single painting. Some artists choose more unconventional tools, such as palette knifes, rags, sponges, fingers, and spray cans. Well-known Abstract Expressionist Jackson Pollock found that housepainter’s brushes worked best to drip, splatter, fling, and smear paint onto his mural-sized canvases, which he laid out on the floor.
Varnish: the role of this solid, relatively transparent layer of resin is to protect the paint surface and intensify the colors; however, solutions made with natural materials tend to discolor or darken with age. Conservators can fix this problem by removing and replacing the old varnish with a synthetic product.
Scale: the size of a painting may speak to its period of origin. Large-scale works grew in popularity at the height of the Paris Salon between 1748 and 1890. The annual or biennial art event exhibited hundreds (if not thousands) of paintings at a time. Limited gallery space and high demand forced many exhibited works to be hung wherever space allowed – even high on walls (and far away from a viewer’s ideal vantage point). As a result, artists increased the size of their supports. Soon artists saw that selling smaller works to the bourgeois for their homes was a more lucrative business. These easel paintings maintained their ranks until the Abstract Expressionists circled back to large-scale canvases
Markings: artist signatures and dates of completion may be found on either the front or back of paintings. These markings help establish authenticity, but not all artists sign their work. Therefore, collectors should look at any labels or stamps on the back of the support or its frame. These can provide information about the origin and age of the artist’s materials as well as about previous sales and owners.