Supports for Painting:
Materials and Practices

DEFINITIONS

Size: any of various gelatinous or glutinous preparations made from glue, starch, etc. used for filling the pores of cloth, paper, etc., or as an adhesive ground for gold leaf on books. In painting, used to seal the support's surface to protect it from acid and make it less absorbent. A size is not a coating; it is a penetrating liquid employed to fill pores, to isolate coatings, or to make surfaces suitable to receive coatings; it is not intended to form a continuous, level film. A size should be very thin, just enough to fill the fibers of the cloth: mix 1.5 oz of rabbitskin glue into a quart of water to create a gel of applesauce consistency. Glue must be prepared by heating without boiling in a double boiler.

"Glue size leaves little to be desired from a functional viewpoint; its incomplete resistance to moisture is its only fault...."

Casein has been recommended for this purpose, because when dry it is much more water-resistant than glue or gelatin; but glue is far superior because casein is too brittle

A modern replacement for glue sizing, is CMC (sodium carboxy-methylcellulose) which has been used for some time in the textile industry. CMC is a cellulose ether, which is chemically compatible with cotton or linen cellulose fiber canvas, and will expand and contract at the same rate as the cloth. CMC remains flexible and will not shed or crack as glue size might do in certain dry conditions. Two coats may be applied with a brush in a low viscosity grade. This product is still in the experimental stage for artistic use; so far I have not heard favorable reports from artists who have tried it, but they may need to adjust the viscosity of their solutions. Mayer warns that "cellulose coatings will form continuous films even when quite dilute, and such films would present a rather precarious bond for the old paint...These materials produce films which are totally foreign in composition and properties to the usual painting materials; this feature may be of greater significance than the fact that they are related in composition to the textile fibers."

Glue: an impure protein gelatin obtained by boiling skins, hoofs, and other animal substances in water and used as a strong adhesive.
Used as a size for painting surfaces, the best for this purpose being rabbit skin glue (especially on a flexible ground) which is flexible and dries out with relatively little tension.

Gluten: the tough, viscid (sticky), nitrogenous substance remaining when flour is washed to remove the starch: Flour Paste.
Generally not recommended for painting purposes, though there are rumors that Bouguereau used a glutenous substance in some way in preparing at least some of his canvases.

Gypsum: a very common mineral, hydrated calcium sulfate, used to make plaster of Paris. Primer for inflexible painting surfaces such as wood panel. (used thinly by early artists on cloth)

Gesso: gypsum or plaster of Paris (calcium sulphate) prepared with glue for use as a surface for painting. Today chalk (as natural calcium carbonate or precipitated chalk - an artificial whiting) is used more commonly than the gypsum that Cennini recommended. Chalk ground was commonly used by Northern painters.

Application of chalk and glue gesso is an art in itself and application must be done methodically and carefully to avoid defects. If gesso is improperly applied, pinholes caused by airbubbles can occur, as well as cracking and peeling from overconcentration of glue, too great a variation in strength of layers (esp. strong over weak), or by atmospheric conditions when applied.

Modern Acrylic "gesso" Polymer primers have come to be used on pre-primed canvas, stretched canvas, and canvas boards. A basic rule of oil painting is that each succesive layer must be more flexible than the last to avoid cracking. And when painting in oils it should be remembered that the ground itself has some degree of flexibility, which normally limits the use of paints to those that are at least as flexible as the priming on the canvas. Acrylic polymers on a cloth support remain more flexible than any oil film. However, "acrylic polymer does not contain the acids which tend to deteriorate cotton or linen fibers. Therefore, the use of a size becomes unnecessary. The absence of glue size and the hydrophobic character of the acrylic polymer produces a very dimensionally stable system. A departure from the rule of applying more flexible layers of paint over less flexible ones is encountered when using an acrylic polymer ground for oil painting.
A survey of this type of construction has shown no detrimental effects of adhesion so far. Layers of oil paint have remained intact over acrylic polymer grounds quite well. The expansion and contraction of the glue size/oil ground construction, due to the absorption and release of atmospheric moisture, is avoided by the use of an acrylic polymer ground. Therefore, the more flexible acrylic polymer layer does not affect the subsequent layers of oil paint as it does not expand and contract as much.
The acrylic polymer ground should not be diluted with too much water as this reduces the effectiveness of the binding resins. Polymer primers that have been diluted to an extreme have exhibited a tendency to powder off or decompose." --Mayer

Certainly the flexibility issue is a mute point when acrylic polymer is used as a ground on a solid substrate such as wooden panels. The greater question is whether acrylic resins will last as long as natural drying oils.

TYPES OF SUPPORTS

INFLEXIBLE
Wood Panel.

The best wood panels for painting are well seasoned, air-dried quarter-sawn hardwoods to avoid warping, bowing, and cupping. Wood types that have been used by artists include: linden, willow, lime, beach, chestnut and walnut, oak, mahogany, and cedar. The best choices of these may be oak, a classic favorite for its strength and resistance to the damp; mahogany, which is extremely durable, has medium to good working qualities, small moisture content, and is of medium price; and western red cedar, used a great deal outdoors because of its reputation for withstanding weather, thus making it ideal as a painting support. A ground made of multiple panels glued together tongue-in-groove with grains running in opposing directions make better supports than one solid board that is more likely to bow and warp.

Other Wooden Supports

Wood emits acidic vapors that are detrimental to subsequent paint films. The acidic deterioration of wood products are most notable in the quick yellowing and decay of newsprint. And framers are well aware of the acid problems associated with cardboard matts and backing boards that necessitate the use of 100% rag PH balanced archival boards for permanent framing since acids from matting can migrate to the artwork and destroy it. Adhesives used in production of engineered wood products "contribute substantially to this chemical reaction" of acidic vapor emission. Therefore, well aged wood panels are preferred.
Protection against these wood acids can be found in the alkali nature of calcium carbonate gesso when used as a buffing agent between the wood and painting. Acrylic Polymer primer is also useful in this regard. Priming should be 1/16" or more for proper protection.

Plywood: a central wooden core sandwiched between a number of thin layers of wood which are glued together.
Blockwood: narrow parallel softwood or, less commonly, hardwood strips glued edge to edge and faced, like ply, with a thin veneer. Comes in 3-ply and 5-ply.
Chipboard: made of chips of wood compressed into rigid panels with synthetic resin glues. Flooring grades compressed to a density of 720 may be used for artists' supports.
Hardboard: a composite panel made by hot pressing steam-exploded wood fibers with some resin, and relies mainly on the lignin that is naturally present in the wood to cement the particles together. The homogenous structure of the board is said to be more stable than solid wood, plywood or blockboard regarding warp. However, some conservators have condemed hardboard due to outgassing and chipping and peeling from the corners. While the marketplace promotes it as a permanent support, conservators have described it as an "excessively self-destructive support at best."
Medium-density Fiberboards: made the same way as hardboard but with the addition of a synthetic resin. They are considered among the most stable boards available and "acceptably permanent." They have a less hard and glossy face side than standard dense hardboard. The "A" grade should be used for artists' supports.

FLEXIBLE
Cloth Supports - stretched over frame or panel
The cloth is the weakest point in the survival of a well-made picture; but advantages of weight, transportability, and the fact that defective paintings on canvas can be repaired or conserved more satisfactorily than those on other supports, have caused linen to retain its position as first choice as a support material ever since it came into general use. The best cloth canvas should be closely woven and of equal thread count in its warp and woof. Single oil primed linen may last longer than double primed because it is more pliable and limber, more supple and less liable to crack when handled than those with thicker coatings. For this reason, large works should be single primed. Smaller works that demand finer paint handling, such as portraits and still life, can be double primed.

Linen Canvas: made from the fibers of the flax plant (Linum usitatissimum) it is a long (24 to 36 inch), strong fiber that creates a more uniform texture than cotton. Russia is the major producer of flax, but the best quality comes from a "200 kilometer wide band of country stretching from lower Normandy through Picardy to Flanders and up into Holland, where there is a great flax-growing tradition." The best finished linen is said to be that made in Belgium.
Cotton Canvas: the seed hair fibers of the cotton plant (Gossypium hirsutum and Gossypium barbadense) are not as long as the linen fibers. The longest cotton fibers are from Sea Island cotton in the United States which has staples of between one and a half and two inches, while average cotton stables run one to one and one eighth inches. These fibers must be spun together to make long threads which increases irregularities and is feared by many to create a weaker strand. It does appear, however, that a good quality loomstate cotton duck canvas of between 12 and 15 oz. is as durable as the more commonly used lighter weight linen and may degrade more slowly in this heavier weight. Light weight (below 12 oz.) should not be used for permanent painting.
Polyester Canvas: a synthetic fiber that creates a tight, dimensionally stable, stiff cloth. It is believed to be more durable than linen or cotton, with a strong resistance to acid attack. It absorbs very little moisture and has exceptionally good dimensional stability, with good elastic recovery. While flexible, it is less likely to stretch out of shape than the natural fibers, placing less strain on the paint layers. It does have a very smooth surface texture, which may not be as good for thickly worked paintings and should be stretched two way before stapling to the support using more staples placed closer together.
Jute: while it is offered for sale, it becomes brittle and is not recommended for permanent painting.
Hemp: A tall, annual, moracious herb, Cannabis sativa, native to Asia, but cultivated in many parts of the world. It produces a tough fiber used for making rope, coarse fabric, etc. Coarse hemp canvas is believed by some researchers to have been the predomenant canvas used by the French prior to the end of the eighteenth century.

Animal Skins

Leather: tanned hide. A non-dyed, non-surface-coated leather should be used for painting supports in order for the paint film to adhere. Stretched over wood panel.
Parchment and Vellum: calf-skin, dehaired, stretched, and scraped, then prepared with chalk and pumice stone. also stretched over wood support.

Paper

Paper is unsuitable as a ground for professional / archival oil painting for many reasons, including the fact that it becomes brittle and weak, is overflexible, and is susceptible to mold, rot, and decay. Works on paper are very fragile and must undergo extreme restorative and conservative treatments, usually within 35 years, even when painted on 100% rag paper mounted to wood panel.
Paper can be used for quick sketches where permanence is not important.

FLEMISH PRACTICES

Painting on Wood Panel

White poplar or oak was used to create the support. To prevent the splitting of the joined planks, one should allow for expansion and contraction without warping. To do this, join your planks with the grain in parallel direction. On the back create several grooves perpendicular to the grain into which you should place cross beams tongued to fit the groove. Do not nail or glue them, but allow for the expansion of the boards to move along the grooves and hold all in place by a loose fitting frame.

Michelle Scalera, Conservator at the Ringling Museum in Sarasota, Florida, told me how early painters would get their wood from the black forest, then age the wood planks through hydration and dehydration before assembling their painting support.

On the back of your panel, protect it from worms and moisture induced warp in the following manner. Coat the back with gesso, size, tow, and a coat of black oil paint. but don't make it too firm so that it may expand and contract with the wood. A work found treated in this manner is still in perfect condition, showing no signs of worm or rot. (on canvas some have recommended that the back be tanned to preserve it and keep out moisture. However, it has been found that affixing a backing board to the frame protects the canvas better. This is the common method used today.)

Size the front of the panel with 2-3 coats of animal skin glue or cheese powder and quicklime. Over this spread 8+ layers of gesso. Apply the first layer thickly on a panel not overly smooth. Then apply at least 7 more thinly. After applying each layer, allow it to dry, sand it, and then apply the next coat perpendicular to the last. This created the bright white ground used by the Flemish in their thin transparent method of painting. The effect was based upon stained glass, where light would pass through the colored resinous layers, reflect off of the bright white ground and reflect back to the viewer. However in Italy, where they were more likely to paint in a grisaille, or dead color in black and white, and then overglaze their color upon it, Vasari recommends 5 coats of size, applied by sponge, and one of priming. While Palomino used only 1 coat of size followed by 1 or 2 of oil priming.

(It is warned that a board so prepared is susceptible to moisture separating the gesso from the board, especially when using the more porous white poplar, as opposed to harder oak or chestnut wood.)

A drawing was then traced to the white gesso ground. Afterwards, it was outlined with brown ink and shaded in full value and much detail. After which it was over primed with a translucent flesh toned oleo-resinous medium through which the drawing could be seen and the white ground was still effective. Usually the drawing was coated with size before the oil prime to keep the oil from absorbing into the gesso ground. This was done to keep the ground pure white. (Obviously this is not necessary when painting on a tinted ground.) Then the colors were applied thinly, at once or in layers.

The process is then as follows:

Wood panel - (Support) not overly smooth on the surface.
Size - 2 to 3 layers. Helps to protect the ground from off gassing produced by the wood as it ages.
Ground - a thick, coarse layer of either gesso (gypsum=calcium sulphate usually used in Southern Europe) or chalk (calcium carbonate usually used in Northern Europe and tinted with pigment, either white or colored) bound with animal glue. Top coat with up to 7 fine layers of the same gesso or chalk applied thinly and perpendicular to each other. Sand between coats until smooth.
(chalk bound with oil is transparent due to the similar refractive indices. This mixture can be used to allow the surface color of the support to show through but should be top coated with oil based layers only.)
Drawing - transfer onto ground from cartoon (preparatory drawing) or draw directly onto ground with brush.
Ink or paint the drawing in monochrome tempera paint, distinguishing the major values and forms.
Size again - 1 to 5 weak coats to make impermeable to oil - keeps the ground white to reflect color through transparent oils. Also prevents dry gesso from leaching oil out of paint film, causing it to dry out and flake off. (modern writers warn against making the ground completely nonabsorbent as this prevents adhesion of the paint film. A light coating of size is preferrable to reduce the surface to a semi-absorbent state.)
Imprimatura - after size is completely dry, apply an oil or oleo-resinous medium tinted flesh tone, light brown, or warm gray. This translucent tone creates a uniform tone over the entire image. Some artists placed this directly over the drawing, using it to seal the gesso or chalk ground in place of the size.
Dead Color - paint the scene or image, defining the forms, values and basic colors.
Carnation - add warmer tones to flesh and final glazes and scumbles to scene to perfect color.
Detailing - accentuate highlights and shadows.
Varnish - addition of resinous or oleo-resinous layer to protect the paint from dirt and abrasion. Also to oil out the colors that have sunken in and create an even sheen.

Final Advice

"The leading methods which have been described differ in many respects from those of the Italian, and in some, from those of the later Flemish masters. Painters of all schools have, indeed, recognized the principle that colours derive brilliancy from light within them; but it was soon found that this object could be attained by various means. it matters not, for example, whether the internal brightness reside in the light ground, or whether it be reproduced at any stage of the work. A preparation of the latter description, answering the same end as the white panel, may consist in a light but very solid painting, by means of which the composition may be defined; and, when such a preparation is thickly painted, the colour of the ground underneath it is obviously unimportant. This conviction may have led to the introduction of dusky grounds; but the indispensable condition of a solid and lighter covering upon such a priming was gradually overlooked: some later Italian pictures exhibit the thin painting of the older Flemish masters on grounds requiring a contrary treatment, and premature decay has been uniformly the consequence. The opposite precaution, though apparently needless, is to be recommended; viz. that of employing a light ground, even when the picture is intended to be solidly painted. This was often Rembrandt's practice: it indicates his having reckoned on the possibility, at least, of leaving his ground; accordingly it is sometimes apparent even in those of his pictures which are (partially) loaded with colour.
It is evident that if cloth be employed instead of wood, and if the ground or preparation be thin, the colours constituting the picture or its substratum require to be applied in considerable body, in order to exclude air or damp from the back. The bad consequences of a neglect of this have been already noticed. There is thus a plain reason for solid painting on cloth, which is not applicable to panels; and, as the Venetian oil painters happened to prefer cloth from the first, their whole process was soon influenced by this circumstance, and differed widely in its means, though not in its end, from that of the Flemish masters.
When Rubens remarked that wood was preferable for small pictures, he may, therefore, have meant that the solidity which is indispensable for works executed on cloth may be too apparent, since small pictures can only be seen near. This and other principles of the kind, founded on a not unreasonable attention to the impressions of the ordinary spectator, were, however, set at nought by those who, like Rembrandt, considered art as an acknowledged convention, and who thought it at least unnecessary to conceal its means. It is also to be remembered, that, if a certain smoothness of surface be desired at last, the substance required may be furnished by a sufficiently thick ground (such as Armenini describes); the solidity of the picture, properly so called, is then not so essential."

This advice is challenged by Michelle Scalera, Conservator at the Ringling Museum, which houses a number of large works on canvas by Rubens, who painted thin, transparent shadows, building up mass only in the lights. These works from the mid 1600s have withstood the test of time on their original linen supports.

The greater issue may be the value of the ground color. Darker grounds will eventually show through thin areas of lighter paint, creating pentimento. Thus, thinly painted images should be done on light grounds. Where a dark ground is used, the midtones and highlights must be built up in greater mass, and in multiple layers.

Painting on Cloth

Throughout the 15th and 16th centuries, and even into the 17th c. in areas of Northern Europe, cloth was considered only for decorative arts such as banners or wall hangings. Patrons preferred their larger and more prestigious commissions to be executed on more durable solid supports - wood panels. "Painted hangings were considered second-rate, even if they were created by well-known artists." (Nico Van Hout) Canvas or linen was therefore used primarily for preliminary studies and for full scale cartoons for embroidered tapestries. Such is the case with the large canvases by Rubens in the Ringling Museum in Sarasota, FL. But in Italy, especially Venice, canvas was used for high art because it could be rolled up and shipped easily. Cloth's light weight also made it appealing and it eventually won out in the North as well.

The preparation of canvas for painting during this period is somewhat odd, and contrary to acceptable practices today, as inflexible gesso was sometimes ground into the cloth. However, this may be the "cheaper form of lead white extended with chalk, known in the seventeenth century as lootwit, as opposed to pure lead white known as schelp-, schilp-, or schulpwit." (see warnings against chalk on cloth below) Abraham Latombe, an Amsterdam painter of the 17th century, "considered a single layer of lead white and umber sufficient, (but) he states that two layers will make a canvas more 'unified.'" "Painters knew that the hygroscopic and rather brittle nature of a chalk in glue ground made it unsuitable for use on canvas, especially when thickly applied and to large scale canvases which might be rolled up for transport," according to Hendriks. She claims that "lead white in oil-based primings, mixed with other pigments (were) usually applied to canvas." Chalk in glue grounds seem to have been an occasional application to cloth and an oddity of the 1600s that may have been determined by cost.

The process for preparing cloth for painting is described by Nico Van Hout. Meaning and Development of the Ground Layer in Seventeenth Century Painting -
Additional comments from Ella Hendriks. Johannes Cornelisz. Verspronck. the Technique of a Seventeenth Century Haarlem Portraitist. Both from the book Looking Through Paintings: The Study of Painting Techniques and Materials in Support of Art Historical Research , 1998
- ISBN 90 6801 575 3 and 1 873132 56 5.

Linen Canvas - (Support) freed of slubs and smoothed with a pumice stone.
Size - Vasari recommends 3 to 4 layers of weak glue applied with a knife to fill the pores of the cloth. Then add 1 or 2 more layers of glue. Armenini's recipe calls for filling the weave with flour, oil and one third fine lead white using a knife, bone, or piece of wood. then coat with 2 or 3 layers of soft glue. (flour is discouraged by Volpato, however, stating that if it is too stiff it will crack and the paint will scale off. But if it is too weak the damp causes the canvas to decay, and the mice eat it.) Others soaked the cloth in glue before laying it out and rubbing it. The goal was to create a smooth surface that would reduce the quantity of chalk to be used for a ground, thereby decreasing the thickness and increasing the flexibility of the whole.
Ground - Chalk or gesso was applied over the size. The difficulty was with a thick layer: "because the ground was less flexible than the support, paint began to flake off, after the canvases had been rolled up." For this reason "Cennini had already indicated that only the interstices between the threads should be filled with gesso (thus banners and hangings could survive continuous movement far better.)" Again Volpato warns that the key is in the glue. A strong glue "spoils the canvas" and "only a very little gesso is required." But despite these warnings, "canvases with thick grounds were still regularly employed in the North, even by the likes of Rubens and Hals."
Imprimatura - Grounds were tinted by adding paint, palette scrapings, or brush washings. Others added an imprimatura (isolating layer) of pigment in oil. Some times Veronese omitted his brownish or flesh-colored imprimatura and painted directly on top of the gesso. Tintorreto usually used a thin gesso layer with a black or brown imprimatura, composed of ochre, charcoal and palette scrapings in oil. But he occassionally omitted the gesso ground and painted with oil paint directly on the sized linen. (It is customary today to prime the sized canvas with a layer of oil paint) Rubens experimented with red-brown gesso primed canvases in Italy, but used grey imprimatura layers over a white or earth colored ground layer when he returned home. (this can be described as a double ground) "The neutral grey tone could function as the mid point in tonal values and could be used to create halftones, shadows or backgrounds."
Drawing - Transferred from a cartoon or drawn on with black or red chalk or painted directly with a brush in oil. Values may be layed in in oil.
Dead Color - paint the scene or image, defining the forms, values and basic colors.
Carnation - add warmer tones to flesh and final glazes and scumbles to scene to perfect color.
Detailing - accentuate highlights and shadows.
Varnish - addition of resinous or oleo-resinous layer to protect the paint from dirt and abrasion. Also to oil out the colors that have sunken in and create an even sheen.

The more traditional and modern method would be:
Cloth Support
Size one or two thin coats brushed on.
Lead in oil Priming (today often substituted with less toxic and more opaque Titanium oil priming or acrylic polymer priming)
An Imprimatura may be added either as a stain or as a double ground, but is unnecessary as a true isolating layer.
Continue with Drawing and Painting.

Just as today, artists worked in different methods based upon their genius and their personality. Some, like Frans Hals, did not bother with preliminary drawings, but chose to work in a more direct manner, as noted by Van Mander:

These fellow-artists go to it, without great pains, working direct with brush and paint with a free approach and thus set down their paintings deftly in the dead-colour; they 're-dead-colour' too sometimes, soon after, so as to achieve a better composition. Thus those who are abundantly inventive go audaciously to work, thereafter making an improvement here and there."

We should learn from this that there is no one right way to paint.
Provided that we apply the technical knowledge of our craft to create lasting pictures, we are free to design our paintings as we see fit.

History, Definitions, and Techniques | Drying Oils and Mediums
Resins and Varnishes | Pigments Past |Pigment Chemistry
Supports for Painting | Grounds on Canvas | Techniques of Past Masters
Discussion with National Gallery Conservator

 Info from: SANDERS-STUDIOS.COM