Painters employed drying oils such as walnut oil and linseed oil occasionally for special effects from the twelfth to the fourteenth centuries. During the fifteenth century oil painting was increasingly used as a fine arts medium, and in the sixteenth century it became the principal painting method in northern Europe and Italy, becoming preferred by many artists over egg tempera, fresco, and distemper painting. The gradual adoption of the oil medium came soon after the systems of perspective and light-and-shade drawing had been absorbed into the pictorial styles of the period, replacing the more stylized almost signlike compositions of the earlier artists. [Editorial note: One might speculate that paint was applied directly onto unprepared surfaces in the early renderings of natural forms and in stylized schema developed in Aegean wall painting not unlike the wall paintings in the caves of Tunhuang along the Silk Road in the Gobi Desert --and an approach to painting which may have arisen out of processes in decorative ceramic ware and, perhaps, writing. European artists during the early Renaissance glazed color with an oil /egg binder over monochromatic light & shade renderings on polished plaster and panels --much in the same narrative spirit of early architectural reliefs which developed in the East and in Egypt. It was not till the high Renaissance that artists had develop the process of mixing pigments together and more directly in the delineation of nuances in imagery. A characteristic of the Renaissance was that attention was brought to focus on the present world with an increasing awareness of changing events and with more fluid and natural exchanges portrayed --less dedication ascribed to the hereafter. The oil paint carried light within the process of delineation.] The characteristics of oil paint proved advantagious to painters who were interested in the effects of light, the description of individual likeness, and the complex variety in nature. That it became almost universally accepted as the standard medium of European and American painting for nearly five hundred years, meeting the requirements of the various styles of painting as they appeared, testifies to its versatility and to its compatibility with the developments in European and American art.
Editorial Note: Much range is provided through the use of oil paints as a media with which to draw, evolve, develop, discover, and define content and imagery. One has the possibility to work with fine glazes or thick applications of the substance through which to develop experience, thought, and understanding. The oil painting media is such that an artist has an opportunity to re-do, re-think, or remove work in the processes of development --and may develop skills to use the media to capture fleeting impressions or to build tangible substances of ideas and impressions. Oil paints may be worked both transparent and opaque.
1.1 Direct Painting Method
Direct painting [also known as alla prima or premier coup painting] refers to a method by which the artist applies each stroke of paint to the canvas with the intention of letting it stand in the picture as part of the final statement. There is to be no retouching or overpainting after the first layer of paint has dried.
Direct methods have been used since ancient times, and the work done during the earliest periods in most cultures is single-layer direct painting. More recently, in Italy in the sixteenth century, in Holland in the seventeenth century, and in France in the nineteenth and twentieth centuries, direct painting techniques have been vehicles for a wide range of pictorial ideas, from the rich sparkle of Frans Hals, to the color directness of Manet, and the frank immediacy of much of the Synthetic Cubist work
Using the direct method the painter, having visualized the way that a portion of the picture should work, attempts to get the effect completely, all at once, without planning to paint over it when it is dry to make it darker or lighter, or warmer or cooler. As each succeeding part is treated, the artist tries to maintain the same pitch, first planning or sensing the final impact of the passage and then trying to bring it to completion on the first attempt. As the work progresses, each stroke must relate accurately to every other color that has already been put on the picture. Ideally when the last bit of bare canvas is covered, the picture is finished, and no retouching is needed.
The great difficulty and challenge of pure direct painting is that the painter must be able to deal with all the problems of the picture at the same moment. For example if the artist is painting a head, when the chin is being painted, each stroke of color must be put on the canvas so that it states simultaneously the location, size, and shape of the chin; the modeling or volume of the chin; the color of the chin under the given circumstance of light; and the way the color unites with all the other colors surrounding it in the picture.
Naturally very few painters have felt bound to adhere strictly to pure direct methods, and so, many pictures, begun in the spirit of alla prima paintings, are retouched, corrected, and elaborated upon after the first layer of paint has dried. However, it is my opinion that the painting is still direct in spirit to the extent that the artist tries to make each stroke count as the final effect. If it is later decided that a particular passage is unsatisfactory, the painter may obliterate the faulty section by scraping it out or by painting an opaque neutral tone over it. The artist may than repaint that area, trying once more to realize the final effect immediately. Technically this may not be direct painting in a single layer or on the first try, but the thought process and range of effects nevertheless relate to the spirit of direct painting.
1.1.1 Technical Procedures
This section . . . . is intended as a general guide and not as a substitute for the personal instruction of an experienced artist. The procedures of other artists and traditions may be useful when they serve as a base from which experiments may be conducted consistent with the individual aims of the artist.
In the case of direct painting, from a technical point of view the procedure is often kept quite simple.
l). On a clean canvas, the general location of large masses can be put in lightly with pencil or charcoal.
2). The palette is set with a complete range of the colors to be used during the sitting, the colors usually being placed near the outer edge of the palette. The palette cup is fastened to the edge of the palette, and a small amount of painting medium is put into it.
3). The colors are thinned on the palette, as they are used, by dipping a brush into the palette cup, bringing out the desired amount of painting medium, and mixing this with a brushful of paint. Colors may be intermixed, although most writers suggest that the mixtures should be kept as simple as possible--that is, they should consist of no more than two or three colors.
4). Colors are applied to the canvas with brushes, palette knives, rags, sponges, or any other instruments. Unsuccessful passages may be removed by scraping them off with the palette knife.
Some painters begin with the darks and gradually work up to the lights; other reverse the procedure. Some employ brilliant intensities from the beginning; other begin with neutral tones. The organization of the picture is, of course, a highly personal matter, and a method that is most suitable and efficient for one painter may be a total waste of time for another.
1.2 Indirect Painting Method
Indirect painting involves procedures in which the final effects in a picture are built up gradually by placing several layers of paint, one over the other, the upper layers modifying, but not altogether concealing, the lower layers.
Indirect painters put their first strokes on the canvas with the expectation that they will paint over them again when they are dry in order to change their effect in some way. Therefore when they put on the first layer of paint, called the underpainting, they do not try for a finished effect, complete in final color, drawing definition, and pattern emphasis. Instead at the beginning of the work they concentrate on one or two of these problems, and they depend upon [and make allowance for] the subsequent layers of paint to develop and modify the underpainting until the remaining problems are finally solved.
Indirect methods of painting have been employed in the past by many artists including Van Eyck, El Greco, and Rembrandt. More recently such painters as Soutine, Modigliani, Rouault, Braque, and Paul Klee have utilized the optical effects of indirect processes.
The existence of indirect painting arises from the fact that although paint may be used opaquely to conceal what is beneath it, it can also be applied so as to be transparent, revealing to a greater or lesser extent what it covers. For example, an oil color, such as cadmium red, in paste consistency may be brushed over an area of thoroughly dried yellow paint. If it is applied evenly and fairly heavily, it will conceal the yellow color entirely. Alternatively the red paint may be thinned with an appropriate diluent and may be spread so thinly over the dried yellow color that it lies over the yellow like a sheet of red cellophane, tinting the area a fiery orange color, while allowing the shape and every surface brush mark on the yellow area to remain visible. The orange tone thus obtained, by superimposing a layer of transparent red on an opaque yellow, will differ considerably in optical character from an orange made by combining the same red and yellow pigments in direct mixture on the palette. The directly mixed tone will have a weighty solid opacity, whereas the orange tone produced through the indirect, or mixture of the two colors will have a more luminous vibration, rather like that seen in stained glass when light passes through it.
By exploiting this characteristic of the oil technique, painters found that they could develop a brilliant luminosity whose exact character was unobtainable in the direct techniques. The procedures most commonly used in indirect painting are called glazing and scumbling.
1.2.1 Technical Procedures
Technical complications and variety increase with indirect painting. One method frequently employed may be described in the following general terms:
l). A brush drawing involving only one or two colors is developed to mark out the important locations and divisions on the canvas. The paint is thinned by means of a "lean" medium (such as 1 part sun-thickened oil, 1/2 part varnish, 3 parts turpentine) to a brushable consistency which flows rather easily.
2). The dark and light contrasts are developed by the use of a "lean" fast-drying white (such as flake white) in all the light areas. In the light middle tones the white is mixed slightly with another pigment (ocher, for example, or Indian red). Darks are produced by adding more color or mixed grays to the white, but all darks are kept much lighter than they will appear in the finished painting. The main effort, at this point, is to produce strong placement and gesture of shapes and volumes. These should be expressed broadly with little surface detail but should be accurate as to the relationship of the larger major pictorial masses. At this stage, the effect of this underpainting must be lighter, both in the lights and the darks, than the artist wishes the finished picture to be...
3). When this underpainting has dried thoroughly, color relationships are developed over the light monochrome by the use of glazes. These may be brushed on and [p. 81] then modified by wiping them down with a rag or a clean brush so that they emphasize and reinforce the drawing and movement of the underpainting.
4). Color effects are strengthened and made more definite by vigorous direct painting into the glazes (either when the glaze has dried or while it is still wet) with substantial strokes of opaque color. Glazes that have lowered the tone of an area too much may be scumbled over with a lighter color to raise their tonality. Drawing and edges are redefined, especially where glazing or scumbling has caused a passage to lose its initial strength.
Notes [on glazing and scumbling procedures in indirect methods of painting]: In considering the many possible variations of this procedure, it is wise to keep in mind a few of the possible difficulties.
A. The glaze tends to darken the general tone of the picture. To compensate for this, the underpainting must be kept considerably lighter than the final painting.
B. The glaze and the scumble tend to create soft, unified, diffused effects. Therefore the underpainting should be strong, even somewhat "harder" than the anticipated final effect.
C. If the quality of the glaze is not relieved by some opaque painting and vigorous redrawing, the total effect of the picture may become too washy, spotty, and transparent.
D. In all indirect processes where more than one layer of paint is anticipated, successive layers should be applied "fat over lean." This rule is explained in the following section.
2. Process of oil painting
The process of oil painting varies from artist to artist, but often includes certain steps. First, the artist prepares the surface. Although surfaces like linoleum, wooden panel, pressed wood, and cardboard have been used, the most popular surface is canvas. While many famous paintings were painted on panel (for instance Da Vinci''''''''s Mona Lisa), the size of the work is immutable and this often makes transportation cumbersome. Stretched canvas, on the other hand, can be unstretched and rolled for easier transportation.
Traditional artists'''''''' canvas is made from linen, but the less expensive cotton fabric has gained popularity. The artist first prepares a wooden frame called a “stretcher" or "strainer." The difference between the first and second is that stretchers are slightly adjustable, while strainers are rigid and lack adjustable corner notches. The canvas then pulled across the wooden frame and tacked or stapled tightly to the back edge. The next step is for the artist to apply a ground (or size) to isolate the canvas from the acidic qualities of the paint. Traditionally, the canvas was coated with a layer of rabbit skin glue and primed with subsequent layers of finely ground chalk (or marble dust) and rabbit skin glue. Later the process was changed to a sizing of rabbit skin glue with subsequent layers of white priming (gypsum, chalk, barium oxide, titianium(IV) dioxide mixed with linseed oil). Modern gessos are made of titianium dioxide with an acrylic binder and are not "real" gessos in the true sense of the word. The artist might apply several layers of gesso, sanding each smooth after it has dried. Sanding the primed surface is important to roughen the generally slick surface so the subsequent layers of oils will properly adhere. It is possible to tone the gesso to a particular color, but most store-bought gesso is white. The gesso layer will tend to draw the oil paint into the porous surface, depending on the thickness of the gesso layer. Excessive or uneven gesso layers are sometimes visible in the surface of finished paintings as a change in the layer that''''''''s not from the paint.
Next the artist might sketch an outline of their subject prior to applying pigment to the surface. “Pigment�may be any number of natural substances with color, such as sulfur for yellow or cobalt for blue. The pigment is mixed with oil, usually linseed oil but other oils may be used as well. The various oils dry differently creating assorted effects.
Traditionally, an artist mixed his or her own paints for each project. Handling and mixing the raw pigments and mediums was prohibitive to transportation. This changed in the late 1800’s, when oil paint in tubes became widely available. Artists could mix colors quickly and easily without having to grind their own pigments. Also, the portability of tube paints allowed for plein air, or outdoor painting (common to French Impressionism).
The artist most often uses a brush to apply the paint. Brushes are made from a variety of fibers to create different effects. For example, brushes made with hog’s bristle might be used for bolder strokes. Brushes made from miniver, which is squirrel fur, might be used for finer details. Sizes of brushes also create different effects. For example, a "round" is a pointed brush used for detail work. "Bright" brushes are used to apply broad swaths of color. The artist might also apply paint with a palette knife, which is a flat, metal blade. A palette knife may also be used to remove paint from the canvas when necessary. A variety of unconventional tools, such as rags, sponges, and cotton swabs, may be used. Some artists even paint with their fingers.
Most artists paint in layers, a method first perfected in the Egg tempera painting technique, and adapted in Northern Europe for use with linseed oil paints. The first coat or "underpainting" is laid down first, painted normally with turpentine thinned paint. This layer helps to "tone" the canvas, and cover the white of the gesso. Many artists use this layer to sketch out the composition. This layer can be adjusted before moving forward, which is an advantage over the ''''''''cartooning'''''''' method used in Fresco technique. After this layer dries, one way the artist might then proceed is by painting a "mosaic" of color swatches, working from darkest to lightest. The borders of the colors are blended together when the "mosaic" is completed. This layer is then left to dry before applying details. After it is dry, the artist will apply "glazes" to the painting, using a process of "Fat over Lean" which means more oil/paint ratio than the previous layer. A classical work might take weeks or even months to layer the paint. Artists in later periods such as the impressionist era often blended the wet paint on the canvas without following the Renaissance layering and glazing method. This method is called "Alla Prima." When the image is finished and dried for up to a year, an artist would often seal the work with a layer of varnish typically made from damar gum crystals dissolved in turpentine. Contemporary artists increasingly resist the varnishing of their work, preferring that the surfaces remain varnish-free indefinitely.
3. How oil paint dries
Unlike water-based paints, oils do not dry by evaporation. The drying of oils is the result of an oxidative reaction, chemically equivalent to slow, flameless combustion. In this process, a form of autoxidation, oxygen attacks the hydrocarbon chain, touching off a series of addition reactions. As a result, the oil polymerizes, forming long, chain-like molecules. Following the autoxidation stage, the oil polymers cross-link: bonds form between neighboring molecules, resulting in a vast polymer network. Over time, this network may undergo further change. Certain functional groups in the networks become ionized, and the network transitions from a system held together by nonpolar covalent bonds to one governed by the ionic forces between these functional groups and the metal ions present in the pigment.
Vegetable oils consist of glycerol esters of fatty acids, long hydrocarbon chains with a terminal carboxyl group. In oil autoxidation, oxygen attacks a hydrocarbon chain, often at the site of an allylic hydrogen (a hydrogen on a carbon atom adjacent to a double bond). This produces a free radical, a substance with an unpaired electron which makes it highly reactive. A series of addition reactions ensues. Each step produces additional free radicals, which then engage in further polymerization. The process finally terminates when free radicals collide, combining their unpaired electrons to form a new bond. The polymerization stage occurs over a period of days to weeks, and renders the film dry to the touch. However, chemical changes in the paint film continue.
As time passes, the polymer chains begin to cross-link. Adjacent molecules form covalent bonds, forming a molecular network that extends throughout painting. In this network, known as the stationary phase, molecules are no longer free to slide past each other, or to move apart. The result is a stable film which, while somewhat elastic, does not flow or deform under the pull of gravity.
During the drying process, a number of compounds are produced that do not contribute to the polymer network. These include unstable hydroperoxides (ROOH), the major by-product of the reaction of oxygen with unsaturated fatty acids. The hydroperoxides quickly decompose, forming carbon dioxide and water, as well as a variety of aldehydes, acids, and hydrocarbons. Many of these compounds are volatile, and in an unpigmented oil, they would be quickly lost to the environment. However, in paints, such volatiles may react with lead, zinc, copper or iron compounds in the pigment, and remain in the paint film as coordination complexes or salts. A large number of free fatty acids are also produced during autoxidation, as most of the original ester bonds in the triglycerides undergo hydrolysis. Some portion of the free fatty acids react with metals in the pigment, producing metal carboxylates. Together, the various non-cross-linking substances associated with the polymer network constitute the mobile phases. Unlike the molecules that are part of the network itself, they are capable of moving and diffusing within the film, and can be removed using heat or a solvent. The mobile phase may play a role in plasticizing the paint film, preventing it from becoming too brittle.
One simple technique for monitoring the early stages of the drying process is to measure weight change in an oil film over time. Initially, the film becomes heavier, as it absorbs large amounts of oxygen. Then oxygen uptake ceases, and the weight of the film declines as volatile compounds are lost to the environment.
As the paint film ages, a further transition occurs. Carboxyl groups in the polymers of the stationary phase lose a hydrogen ion, becoming negatively charged, and form complexes with metal cations present in the pigment. The original network, with its nonpolar, covalent bonds is replaced by an ionomeric structure, held together by ionic interactions. At present, the structure of these ionomeric networks is not well understood.
4. Simple Rules
Simple Rules for Painting in Oil - The following concise outline touches on the more important points to be observed:
1). Use a white ground which is firmly anchored to its support.
2). Canvas should be prepared with oil or acrylic grounds; emulsion or gesso grounds belong on panels.
3). Be sure there is good adhesion between paint and ground.
4). Use sufficient paint to produce a full, normal paint coating so that the final picture has the desired paint quality, but do not overload the work with extremely thick or exaggerated impasto. Avoid, at all costs, a continuous, thick, pasty layer of paint; heavy or thick impasto strokes are best used in isolated spots.
5). Remember the basic rule for all paint coatings and layers other than acrylic grounds--that is, always paint flexible coats over less flexible layers, and never use brittle coatings over flexible ones.
6). The degree of absorbency and texture of the ground should be suited to the type of painting. Control of paint and its permanence are greatly influenced thereby.
7). Thin the paint with a little turpentine when desired; avoid the excessive use of painting mediums and emulsion-stiffened whites except when the occasion calls for glazing and work that requires precise control.
8). Remember that previous painting or underpainting has some effect on the final results and that careless overpainting may lead to unwanted effects.
9). Oil paintings that are to be varnished should be allowed to dry for 3 to 6 weeks before varnishing, but it is better to varnish [p. 131] them too soon that to put them into circulation or exhibit them unvarnished.
10). Use fresh colors that have not thickened on the palette.
5. Basic Principles
Basic Principles Applied to Oil Painting . . . . An oil painting must be considered as a structure. Therefore, just as a building, a highway, or a bridge must conform to age-old principles of engineering, so an oil painting must conform to long-established rules which govern the building-up of layers or coatings, superimposed one over the other. Since the ground, the paint layers, and the individual ingredients of these are all elements of the whole painting, they must be built up in relation to each other and to the whole in order to obtain satisfactory results.
One of the most important of these rules is the previously mentioned [Rules of Gradation of layers] admonition never to paint coats over more flexible layers, or else cracking will occur. When painting on an oil canvas, you should remember that the ground itself has some degree of flexibility, which limits the use of paints to those that are at least as flexible as the priming on the canvas. An exception to this rule may be made when using an acrylic polymer ground.
6. Special Effects
The best way to insure permanence in oil painting is to keep the process simple, not to stray too far from the simple rules and regulations when painting with linseed oil colors, and to obey them very carefully when using poppy oil colors. The attempt to duplicate some of the effects of the seventeenth-century Flemish artists has led some painters into complex and troublesome procedures, when, as modern investigators have so often pointed out, the materials of these older users of the oily mediums were not so very different from ours. Their oil paints were perhaps somewhat more fluid and less stiff or plastic than ours; resinous painting or glazing mediums were added to them only when the thin glazes and other special manipulations were involved. Sometimes, however, an effect created in certain areas, especially where white lead and flesh tones and other pale tints made with white lead were used, displays crisp linear or impasto definitions which defies reproduction when we use the more softly blending whites which we now buy in tubes.
One way to make flake white crisp and useful for sharply textured effects for under- or overpainting is to mix in a little egg yolk by working it into the point thoroughly with the palette knife. The egg yolk must be added a little at a time, until the desired manipulative properties are obtained, avoiding an excess which might produce tempera or water-soluble paint. For the same reason, neither turpentine nor water should be added during the mixing, although the paint may be freely diluted with turpentine during its use. This mixture is a dual emulsion in which oil is the surrounding medium or external phase, and it can be handled and thinned like any other opaque oil paint except that it dries or sets up more rapidly. It tends to dry to a mat and somewhat coarse finish.
Another means of achieving this crisp handling quality is to grind titanium or zinc white to paste consistency in whole egg and mix two parts of it thoroughly with two to three parts of flake white tube oil color. Some artists use an egg-and-oil tempera emulsion, such as the one mentioned on page 145, instead of straight egg; the entire procedure requires a little experimentation to suit the individual personal requirements, and the resulting dried paint films have to be carefully examined to see whether or not they are tough and flexible enough before adopting any such mixture of materials for continual use, especially on canvas. Casein paints will also mix with oil colors in the same way, but the combination of casein and linseed oil is not recommended because of rapid after-yellowing and embrittlement of such mixtures on aging. Ready-made textural whites of this nature are sold in tubes under proprietary names; these are believed to be of synthetic-resin origin.
Throughout the nineteenth century a number of complex painting mediums were added to oil paints in order to alter their brushing qualities, and virtually all these have been discarded because of the rapid decay of the paintings in which they were used. Chief among these offenders was a jelly-like substance with a curious name, megilp. Made by mixing heavy mastic varnish with a linseed oil that had been cooked to blackness with litharge or white lead, this material was used with oil paints to impart a brushing quality that overcame many difficulties, at the almost certain cost of the eventual disintegration of the painting. History teaches us that the wisest course is to adhere to the simple oil paint technique as much as possible, to use oleoresinous painting mediums with restraint, and to avoid complex jelly mediums.