paintings, what they are made of, their anatomy, and terminology
canvas paintings
the adjacent images show the typical front and back views of a canvas painting.
The traditional manufacturing technique
Canvas paintings are made in the following manner: first, a canvas is stretched on a wooden frame. the canvas consists of a regular woven textile consisting of cotton, linen, hemp, etc. The canvas is stretched by pulling its edges and nailed (or stapled) to the wooden frame to keep the canvas flat and taut. The wooden frame, referred to as the auxiliary frame, can either be a strainer or stretcher. A strainer consists of a simple frame that has its corners adhered together with nails or adhesive. A stretcher, however, does not have its corners adhered together (with nails or adhesive) in order to permit the frame to expand and slightly increase its outer dimension. The latter expansion occurs by wooden keys (triangular-shaped wooden parts) that are found in pairs at each corner of the frame. the tapered keys can be gently hammered to push each member of the frame to separate a bit more from each other. Stretchers are intended to increase the painting's tautness whenever it slackens by expanding and increase the frame's dimensions. (The latter is a delicate operation that can cause paint detachment and it is recommended to ask for professional advice). Therefore, it is possible to differentiate a strainer from a stretcher by taking a look at the painting's reverse side and check for the presence of wooden keys at each corner of the frame. The following photograph is a detail of a painting's reverse side, showing two wooden keys inserted at each corner of the frame.
A liquid adhesive, typically consisting of an animal or fish glue diluted in water, is then applied by brush on the canvas. This procedure is referred to as sizing and is mainly intended to increase the rigidity of the canvas. consequently, the sized canvas is coated with a thin preparatory layer (or ground layer). this layer can consist of powdered hydrated gypsum or chalk mixed with a drying oil, animal or fish glue. This coating often contained a reddish powdered paint to obtain a preparatory coloured base on which to paint.
Consequently, paint is applied. paint is made first by crushing a material having the required colour. For example, to obtain blue colour, the semi-precious stone called lapis lazuli can be finely ground to obtain the natural ultramarine colour (refer to the following two images). The finely-powdered material (referred to as pigment) is then mixed with an adhesive in order to remain adhered to the painting and to be easily brushed. The latter adhesive, referred to as medium, generally consisted of a drying oil such as linseed oil. mixing pigment with oils would make oil paint. other mediums that were less commonly considered for canvas paintings include glues originating from animal or fish (the mixing of pigment with animal/fish glues is referred to as tempera magra); or egg with/without a drying oil (referred to as tempera grassa). some rare examples of canvas painting also included an extremely thin sheet of real/false gold adhered to the painting with a drying oil - referred to as oil gilding - or armenian clay/bolo - referred to as water gilding.
Paint can be applied in several ways. it can be applied thick to obtain texture. the thick application of paint is referred to as impasto. but paint can also be applied thinly and evenly. in addition, it is possible to apply an extremely thin and semi-transparent coating (particularly effective with a particular range of pigments) that are referred to as glazes. glazes can be applied for several reasons. generally, glazes are applied to retain the underlying colours visible... or to create a very special effect - such as applying blue and, once dried, a thin transparent yellow glaze can be applied over it to obtain a very nice green colour.
Once paint is applied and left to dry, a transparent protective coat can be applied over the painting - referred to as varnish. varnishes used to be consist mainly of a natural tree resin, such as dammar or mastic, that are diluted in a chemical solvent and applied on the painting by brush. varnishes not only protect paintings, but also increase the colour saturation of the painting, making colours look slightly darker, more intense and more glossy. it is also important to note that, ideally, varnishes are applied 6-12 months (or more) after completing a painting because oil paints take a very long time to dry completely.
Thus, in a few words, canvas paintings are made of many different materials that are adhered together. if one had to imaginably divide a canvas painting in two parts, it should look like the following image:
the anatomy of a typical canvas painting
Today's ready-made canvas paintings available from art shops
Today canvas paintings can be bought ready-made from art shops. many artists choose to do so. usually, commercial canvas paintings consist of a very thin cotton canvas stretched on a wooden stretcher. the canvas is primed with a white acrylic-based preparatory layer and can be painted over with oil paint or acrylic paint.
Regarding the permanence of such commercial canvas paintings, one must note that the extremely thin canvas is easily worn out after a few decades. they can easily rip, particularly around the edges where it is bended around the wooden stretcher frame. the choice of using cotton canvas presumably lies mainly in the cotton's low cost, and not because it is the best canvas for paintings. in fact, a few manufacturers choose to offer the more expensive linen canvas that by time cause less paint cracks and detachments. moreover, the application of a white acrylic primer is done because of the acrylic's considerable flexibility which resists cracks and is suitable for both oil and acrylic paints, making it more commercially viable. but an acrylic-based preparatory layer may not be ideal for oil painting because if an oil painting (painted on a commercially-prepared canvas painting) requires chemical cleaning by paintings conservators, the chemical solvents used for oil paints may partly dissolve the underlying acrylic preparation, causing damage... of course becoming a potential nightmare for conservators who will do their best to avoid such damage. and, finally, manufacturers of canvas paintings refrain from saying exactly which materials they use to produce their canvas paintings... possibly a secret that is well guarded to prevent others from copying them. not knowing what materials are used, one can not exactly tell if they are permanent and if the manufacturers are really interested in producing art materials that can be effectively treated by conservators in the future - once the materials deteriorate. to top it all, manufacturers change their materials generally without notice.
In a way, the new culture of going to art shops to purchase ready-made canvas paintings has distanced artists from the fascinating world of handling and testing different canvases and preparatory layers. it is possible to manufacture a canvas painting from scratch and it is very rewarding indeed because one can learn a lot how to handle materials and obtain the desired final effect of a painting. paintings become more personal too. but, of course, it should be also mentioned that manufacturing paintings from scratch is time consuming and a bit more expensive. in addition, a new breed of paintings conservators are studying modern art materials together with conservation scientists in a collective effort to establish new conservation treatments that are adequate for the conservation of modern materials. fortunately, some art manufacturers are also willing to work hand-in-hand with conservation specialists to formulate more permanent materials that can also be treated by paintings conservators.
artandconservation.net by David Frank Bugeja is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 2.5 Malta License.