canvas
A canvas is a fabric made of linen , which is stretched on a stretcher frame or in a support frame . It is used in numerous painting techniques, e.g. B. oil painting and acrylic painting, as a base.
General
The advantages of canvases over other image carriers such as wood, metal and walls are their low cost, low weight and flexibility (roll up for transport). The disadvantages are a lower stability and the risk of breaking the paint layer. The texture in the work, which is caused by the canvas as a base, can be a desired effect, but it can also be perceived as a disadvantage.
Suitable substances
Many fabrics made from both natural and synthetic fibers are suitable for painting . The fabric structure has a significant influence on the material and design effect. The different art eras also had their different preferences. In the older art, fabrics made of hemp fiber were preferred , which were very robust. The knots found in every hand-woven fabric were beaten flat with a hammer. When they were pre-glued several times, they were repeatedly sanded in between to make the surface as smooth as possible.
Industrialization brought the possibility of mechanically woven fabrics. During this time, cotton fabrics spread among artists. In modern painting, people found their way back to hand-woven hemp fabrics and consciously used structure as a design element. Today's canvases are usually made of cotton or linen. Cotton is cheaper but less flexible - marks in the fabric can remain. Linen is more expensive but more flexible and it can withstand higher loads. Large pictures are therefore usually made of linen.
Covering the canvas
The covering of canvases requires a certain skill and practice. The untreated fabric is stretched straight and loosely on a wooden frame. You always stretch diagonally crosswise, so first the top left corner, then bottom right and so on.
The untreated fabric is stretched through the line (see below). The wedges, which modern frames have on the back, are not used to correct unsuccessful covering, but to compensate for changes in tension due to changes in humidity and temperature. Care should be taken when wedging the prepared canvas, as a possible over-tensioning cannot be reversed. If the fabric has already been primed, it is stretched taut - but this is not recommended for larger pictures because the fabric quickly wrinkles.
In principle, when it comes to covering canvases, a distinction is made between a stretcher and a strainer. The stretcher became popular in the 18th century and is still the preferred type of frame construction today. The historically older variant is the strainer, which was already widely used in the 16th century.
Canvas on a stretcher
Covering the canvas
Pre-gluing
Once the fabric has been stretched, it is treated with a so-called pre-gluing, i.e. a very diluted glue solution. Nowadays there are modern binders like acrylic that are very "good natured". The old technique used bone glue , which is a little more difficult to process. Bone glue must be carefully heated, preferably in a water bath, so that it does not burn. These glues are the strongest natural glues we know. You can also use them to stretch large canvases. If you let the glue stand too long, it will smell very unpleasant.
Other possible ingredients and additions
Since the bone glue remains water-soluble after drying, it is unsuitable for water-based painting techniques. To reduce the water solubility, alum (potassium aluminum sulfate) is added to the glue . This causes the protein content in the glue to precipitate and ensures additional binding through protein chains, which later dry insoluble - comparable to the binding agent casein (cheese substance).
Another method is to add eggs. The resulting egg tempera is not as flexible as glue and tends to break quickly. This disadvantage does not play a role on rigid picture carriers such as wooden panels, where it can then be used without hesitation. These egg tempera primers take longer to dry completely than pure glue primers.
The primer
Before the canvas can be used, it must be primed. There are some examples of modern painting in which it was deliberately omitted as a creative means. The primer is used for preservation, and a light primer enhances the luminosity of the colors. Unprimed fabrics become brittle more quickly.
Rembrandt preferred a dark brown primer, which gives his paintings a dark, warm look. Rubens preferred the white plaster base with a light blue-gray shave.
Light primer
Glue is almost colorless . For a white background, white pigments are therefore added to the primer . This offers chalk , zinc white and titanium white to. The previously popular but poisonous white lead is no longer used; instead, titanium white, which has better opacity, is usually preferred. In addition, unlike white lead, titanium white is chemically inert . Since titanium white is relatively expensive and large quantities are required for the primer, it is sometimes also stretched with the cheaper zinc white or the even cheaper chalk . The chalk should be " soaked " in water for about 24 hours beforehand, because it has enormous suction power, which can otherwise negatively affect the drying behavior.
The more chalk is used, the more absorbent the base becomes. This can go so far that the entire binder of the paint is sucked off and the paint looks very matt and partly "chalked off" (i.e. the paint is not "smudge-proof"). Even after it is completely dry, the paint can remain on the hand when it is touched because there is no longer enough binding agent to form a closed paint film.
Paint rollers have proven effective for applying the white primer.
Depending on the primer, it should be noted that the primer contracts when it dries . This is important when covering the frame (if the canvas is only primed after covering), because especially with large formats, the pressure on the frame can become so great that it breaks when the primer dries.
Plaster bases
The much-mentioned plaster of paris grounds are not stucco plaster or the like, which sets after adding water, but rather chalk grounds .
Paper covering
What is meant is not that the paper is attached directly to the wooden frame, but rather on the fabric covering, as it were as a primer with all the advantages and disadvantages that paper has, such as the strong tendency to yellow when exposed to sunlight. This is a special technique that is not widely used. It is only worth mentioning in connection with the Dada movement and its collages .
insulation
Before the actual painting process begins, so-called insulation is often applied. On the one hand, this has the task of regulating the absorbency of the painting surface and, on the other hand, it is for creative reasons. For example, Rubens deliberately used irregular, striped gray-blue insulation. Anyone who has ever tried to create the preliminary drawing on a bright white background will know how difficult it is to find the right proportions, especially with large-format pictures. Therefore, the evenness is deliberately broken. Anything that is “lean” enough (see below “fat on lean”) and has little tendency to yellow can be used as material.
"Fat on lean"
A rule of thumb that should always be taken into account when composing a picture (and that applies to the entire picture - not just the primer) is: "fat on lean". "Fat" means rich in binder and "lean" means low in binder. So always a layer with a higher binder content on top of a layer with a lower binder content. For two reasons: on the one hand, to avoid tension between the individual image layers, and on the other hand, to ensure good adhesion. There is also a fat-on-lean hierarchy between the individual binders , so the water-soluble ones are the lean ones and the oil-soluble ones are the fat ones. Fat binders physically expand as they dry; So oil paint, for example. The lean ones, on the other hand, contract; very extreme for example, casein - Tempera . If you were to try to apply a casein paint to an oil paint, it would on the one hand roll off and on the other hand (if you emulsify it by adding egg and still make it stick) after a short time under the expansion of the oil paint.
See also
- Bookbinding canvas
- Screen (originally and commonly canvas )
Web links
Sources and individual references
- ↑ What is canvas?
- ^ Mayer Ralph: The Artist's Handbook of Materials and Techniques . Viking Adult; 5th edition (1991), ISBN 0-670-83701-6
- ↑ Stretcher versus Strainer ( Memento of the original from June 12, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
