Originally written and published in 2000, this article still contains a lot of great information, but any products specifically mentioned should be checked that they're still carried at Opus (Stevenson for example has gone out of business). Also, the way it's written could probably be updated/improved to your more engaging standards.  

At Opus, we strive to inform our customers about the art materials we carry and to offer quality technical information so that you can make informed decisions about the products you are purchasing. We felt that an informational supplement on oil painting was long overdue as this is a topic that is often asked about in our stores. As many of the materials needed to set up an oil painting studio do involve toxic components, our intention with this supplement is not only to offer you choices about the many materials available but to let you know about some of the newer alternatives which may be more practical as well as health-conscious.

For those who are just starting out, the long tradition of oil painting may seem like a very involved and complex process. Likewise, for many experienced oil painters, the opportunity to experiment with materials might be enhanced further if more quantifiable information was available on what many products actually do. We also realize that all artists approach materials, mediums, and the working process differently, therefore Opus endeavors to stock everything from the most traditional of mediums and purest of turpentine to some of the more recent alternatives such as synthetic varnishes, citrus thinners, and brush cleaners. Like many products, each brand of oil paints and mediums is made differently and requires some investigation to find which will best suit your painting needs. Whether you are a beginner or an experienced oil painter, it is always best to remember to read labels, test first, and to experiment fully with your materials.

Please refer to the charts on pages 2-3 of this insert for a look at our canvas selection and to compare the various types of solvents we carry. We have also included an oil painting glossary on the back page to clarify the italicized terms used in this supplement. More specific health and safety information on solvents can be found in Material Safety Data Sheets (MSDS). Should you like more comprehensive information on any of the materials that Opus carries, please ask our staff for further assistance.

Oil painting developed over a long period of history and was in use as early as the 13th Century. Its early application was primarily for decorative purposes and it was not applied as a fine art medium until much later. Traditional egg tempera was the medium of choice for artists in Europe for many centuries prior to the introduction of oil painting, which did not gain acceptance until the 15th and 16th centuries. Flemish and other European painters initially combined oil paints with egg tempera techniques and materials. The Italian painters of the Renaissance continued to develop oil painting techniques and eventually adopted oil painting as a medium of its own standing.

Oil painting has sustained its popularity among many painters as it is perceived as a reliable and long-lasting medium. The luminescent quality and color of oil paint also make it an excellent choice for techniques involving layering or glazing effects. It should be noted here, that oil painting does provide a working process that is distinct from other painting mediums. While there is often a tendency to compare oil and acrylic painting, they are in fact two very different mediums that produce very different results. The perceived complexity of the oil painting process is perhaps due to the use of solvents and other oil-based mediums, which require care and a certain understanding of how materials interact or mix with one another. There is a long tradition of skilled artists and "masters" that accompany the history of oil painting, which in turn has produced a mystique of inaccessibility. Like many artistic mediums, however, practice, research, and a safe studio can go a long way to enjoying the versatility and accessibility of oil paints.

Today, advancements in technology and environmentally friendly products provide improved and safer options for artists, in oil painting materials, and cleaning supplies. Citrus-based thinners and mediums, odorless mineral spirits, brush cleaners, and hand cleaners are available as alternatives to using turpentine and other solvents for cleaning your brushes and hands. Water-soluble oils and mediums eliminate the need for any thinners and solvents and are an ideal alternative for artists with sensitivities to more traditional oil painting materials. Also, barrier creams and disposable gloves help prevent exposure to pigments and liquids which can be absorbed through the skin. All in all, artists, art educators, art material retailers, and manufacturers are more aware of the importance of alternative materials and safety products.

When properly applied, oil paints produce exceptional color, depth, and stability. Oil paints consist primarily of color pigments suspended in a drying oil, such as linseed oil. Due to the transparency of linseed oil, the color that you apply does not change to any great extent when dry, and when materials are carefully selected and applied, oil paints will not deteriorate over time. The oil that the pigments are suspended in also contributes to the slower drying time of oil paints. This allows the artist a greater working time than that of watercolor, tempera, or acrylic paints. This extra working time allows changes to be made over many sittings and enables the artist to blend, remove, and add new paint as needed without the use of extenders or mediums. The low viscosity of most oil colors enables the artist to explore both heavily textured mark making or soft, almost invisible brush marks within the same piece and with the same materials. A wide range of light and color effects, ranging from bold opaque effects to transparent glazes, can also be experimented with.

Unlike acrylic paints, oil paints dry by oxidation as opposed to the evaporation of moisture. Oxidation is a fairly slow process, which results from the oil portion of the paint absorbing oxygen from the atmosphere. This "drying" process produces a hard and durable film of paint. If the paint is applied too thickly, however, oxidation can cause cracking or wrinkling during the drying process. It takes anywhere from 3 to 12 months before an oil painting is completely dry, and although the surface layer may appear and feel dry to the touch, the underlying layers are unlikely to be completely dry. Oil paintings can only be varnished when they are completely dry, otherwise the paint film is susceptible to cracking and rippling.

Alkyd oil colors are made for painters who require a faster drying oil but not one that dries as fast as acrylics. These paints differ slightly in their ingredients from regular oil colors as they are composed of oil-modified alkyd resin instead of a slower drying linseed oil. They can be thinned with conventional oil painting solvents such as mineral spirits and are great for techniques such as glazing and impasto where it might normally take weeks for your work to dry. Alkyd fast-drying oil colors will stay workable up to 4 to 8 hours and will be dry to the touch in 24 hours. The drying time for all oil colors, whether traditional or alkyd, varies depending upon how thickly they are applied and the temperature of your surroundings. Different colors also dry at different rates, as the pigments used are in fact chemical elements that each behave in different manners. In addition, there are oil painting mediums that are designed to speed or slow the drying time of these paints.

Both artist and student grade oil colors use genuine and synthetic pigments. The primary difference is that the proportion of pigment is much smaller in student grade paints in the interest of economy for the student or beginner painter. In addition, some student paints will use synthetic hues of a particular pigment instead of the genuine pigment color. With less pigment overall in student colors, the bulk of the paint is made up by additives and the resulting color is not nearly as rich as that of artist oil colors. If you are a beginner oil painter, student oil colors are the most economical method for learning the medium, and once you become more confident with the medium you can advance to artist quality oils, to enrich and expand your palette.

Indirect painting is a method which involves the build-up of multiple layers of paint and medium. Artists such as Titian, Rembrandt, Rubens, and Da Vinci used this method of painting. This method can be broken down into three basic and distinct layers. First, a dark transparent underpainting of one or two similar colors is used to block in the basic forms of the painting. Second, a middle layer made up of opaque colors is used to build detail and form in the painting. Thirdly, the final glaze layer is added to either emphasize or mute previously applied layers to create richness and depth in the work.

This method of indirect painting follows the fat over lean rule. It is important to remember that all painting mediums are considered fat, and thus a mixture of solvents and mediums must be used to make the paint more lean for the first layer or two. All subsequent layers should have little or no solvents to ensure that they are fatter than the layer before. As a basic rule of thumb, artist grade oil paints that appear shiny tend to be fat, and artist grade oil paints that look matte are lean. Following the fat over lean rule will help to prevent cracking in your paintings by avoiding having the top layer of paint dry faster than the layers underneath. The indirect painting method can then be altered to create different effects. The initial layer can be made with light, transparent layers as opposed to dark, or for brighter paintings thin, transparent glazes can be added between the first and second layer, to modify the initial opaque underpainting.

Direct painting is used to make paintings in one sitting. This method is ideal for paintings that are made with either thick layers of paint or transparent glazes. It relies on a great deal more planning by the artist as color and form must be chosen simultaneously, and due to the immediacy of the technique, instinct and chance greatly influence this form of painting.

Historically, the Impressionists, Fauvists, and Abstract Expressionists favored direct painting. Traditional direct painting can be further divided into two categories: Plein Air and Alla Prima. Plein Air is a method of painting landscape entirely out of doors and Alla Prima is direct painting in a single paint layer on a white ground. When using direct painting, it is best to paint from light to dark and from the background to the foreground to achieve the best results. Variations in brush stroke and style, and moving from mid-tones to increased contrast tones will add complexity to this technique and enrich your painting. Since direct painting relies on the use of wet-into-wet, a small amount of medium will help to increase the fluidity of the paints. Oil painting is not limited to these two general categories. Most artists use a combination of painting techniques and with experimentation you will find which combination(s) work best for you.

• Impasto: The use of thick layers of paint to create texture.
• Imprimatura: The application of a wash or glaze of color that tones the canvas before beginning a painting.
• Sfregazzi: Italian for light rubbing, this technique uses glazing to create shadows over already existing light areas.
• Sfumato: Italian for softened, this technique is a softening of transitions, especially from light to dark.

In addition to various techniques, tints, shades, and tones of oil can be used to enrich your palette and vary your images according to subject matter. Tints are often used to make bright paintings because, as the light hits the painting, it will reflect off both the paint and the support beneath the oils. Shades can assist painters in making luminous paintings while keeping whites and tints for highlights, and tones can help you build paintings through the use of value (pure tints and grays). Tints, shades, and tones are made as follows:

• Tints: A combination of pure color and white. White is added to the pure color to make a tint.
• Shades: A combination of pure color and black. Black is added to the pure color to make a shade.
• Tones: A combination of pure color and black and white. Black is added to a tint to make a tone.

Solvents and thinners are used for thinning paints to a working consistency, diluting oil painting mediums, dissolving varnish resin crystals and waxes, cleaning paintings for the purpose of restoration, and general studio clean-up. They are referred to as solvents when used to dissolve solids such as varnish resin crystals, and as thinners when used to dilute liquids such as painting mediums. Solvents such as turpentine and mineral spirits are naturally based products, whereas, paint thinners are most often synthetic variations. It is best to use naturally-based solvents and mediums with oil paints, and more economical synthetic thinners for studio clean up. All solvents and thinners should be used in a well-ventilated area, even if classified as "odourless," and should be stored in their original containers.

Citrus thinner is a citrus distillate and a by-product of the manufacture of citrus peel liquor. It has a yellowish color and a lemon/orange odor. It is classified as an extra-mild thinner, or one that is not as strong as turpentine. It is best used as a turpentine substitute for thinning paint and cleaning brushes but it is not strong enough for dissolving damar resin crystals. Citrus thinner speeds the drying time of oils. Citrus thinners are also more environmentally friendly than pure turpentine and are useful for people with chemical sensitivities. Although citrus thinners are generally lower in toxicity, they should still be used with precautions and in a well-ventilated area. Citrus thinners are flammable.

Mineral Spirits are a petroleum distillate with properties similar to turpentine. Some artists prefer mineral spirits to turpentine because it leaves no gummy residue, does not deteriorate with age, is cheaper, and causes no apparent reactions in people sensitive to turpentine. Mineral spirits can be used as an oil painting medium in place of turpentine, but like citrus thinners, it cannot be used in recipes containing damar resin crystals, as it will not completely dissolve the resin. Mineral spirits can also be used to clean brushes and other tools. This product is also manufactured as Odourless Mineral Spirits. Mineral Spirits are a practical alternative for paint thinning and studio clean up. Although it has no apparent smell, it should still be used in a well-ventilated area.

Paint Thinner is a synthetic variation of natural based solvents such as turpentine or mineral spirits. For this reason it is more suitable for clean up than for use as a solvent for mixing with paints or mediums.

Turpentine is the traditional material used to dilute oil paints. Artists should use only pure gum turpentine for oil painting. Industrial grade turpentine, which is generally available in hardware stores, contains impurities and a strong, unpleasant odor. For any recipes containing damar, for making painting mediums and varnishes, turpentine is the appropriate solvent. This and the Eco-House product, Natural Orange Terpene Solvent will dissolve damar crystals. The gummy residue left after evaporation is harmless, although turpentine is best when it is fresh. It should be used in a well-ventilated area.

Varnishes are used to protect paintings from dirt and atmospheric pollution. They are meant to be removable for cleaning and restoring paintings, so that the old varnish can be replaced with a fresh coat. Varnishing also helps to give paintings a consistent look, as oil painting techniques are known for creating paint surfaces that have an uneven quality. As painting grounds are often variably absorbent, one pigment may react differently from another resulting in a varied surface of dull and shiny spots. Varnishes can provide consistent coatings in either a high gloss, matte, or satin finish and should be thin, clear, non-yellowing and flexible, in order to adapt to the inevitable expansion and contraction of the painting support.

Picture Varnish is a final coating for oil, alkyd, or acrylic paintings. It creates a uniform finish and protects the painting from dirt and atmospheric conditions. Picture varnish should only be applied to a thoroughly dry painting: for oils, one which has been drying for about 6-12 months; for alkyds, 1-2 months; and for acrylics, 24 hours to 2 weeks. A painting with delicate glazes may take less time to dry and should not be left unvarnished for too long.

Retouch Varnish is made of the same solution as that of picture varnish, however, it contains more turpentine. As a result, it will not form a skin or create a high gloss when it is sprayed or applied with a soft brush. The purpose of retouch varnish is to recreate the original color appearance of wet paint on areas where the paint has dried out or appears to have sunken-in. It is only applied to areas that have dried, making color matching of new and dry areas easier. Some sunken-in areas will require more than one coat of retouch varnish to retrieve the fresh appearance of wet paint. It should be applied in very thin layers and be allowed to dry thoroughly between coats.

Damar Resin is tapped from the damar fir tree and is found chiefly in Indonesia and Malaysia. It is the most traditional varnish for oil paintings. It is available in clear or slightly yellowish, dusty crystals about 2.5 to 5 cm (1 to 2 inches) in diameter. Pure gum turpentine is the solvent of choice for dissolving damar crystals, as other solvents either dissolve the resin incompletely or are difficult to store safely in the studio. One exception to this rule is Eco-House Orange Terpene Solvent, which is strong enough to dissolve damar resin and is designed as a substitute for turpentine. Damar varnish yellows and its film becomes brittle with age. This is caused by exposure to ultraviolet light, present in most lighting systems, and is unavoidable unless special filters are used over the light source. This deterioration is also caused by oxidation, which in turn is increased by exposure to ultraviolet light. Although damar is a reversible varnish, its repeated removal and replacement to counteract yellowing are significant problems for conservators charged with the care of work, since the process can ultimately be harmful to the painting.

A painting ground is the prepared surface on which the paint is applied. Usually, it is an absorbent, white surface designed to reflect light off the pigment molecules in the paint. Gesso is the traditional oil painting ground, made from a mixture of chalk, white pigment, glue, and water. True gesso is best applied to a rigid surface such as unfinished wood or masonite panel as it is generally too brittle for fabric supports.

The ingredients are mixed in a double boiler over low heat. The glue in this process serves as a binder to create a smooth, easy to spread gesso, which is free of bubbles. The gesso is then applied to the support in successive coats at right angles to one another. The final coat must be sanded to remove the brush strokes and left to cure for at least two weeks. When oil paints are eventually applied to the surface, the gesso is very absorbent. This provides a good bond between the paint and ground. If high absorbency is not desired, a highly diluted coat of varnish can be applied over the gesso before you begin painting.

Oil-based grounds are ideal for both wood and fabric supports. If you are using a wood or masonite panel to paint on, you can apply the oil-based ground directly. If you are using a fabric painting support, you must size the fabric with Rabbit Skin Glue or PVA (polyvinyl acetate) first. Oil ground is a solid coat of white oil paint specially formulated to act as a ground upon which subsequent layers of oil color will adhere. Oil grounds are usually thinned with mineral spirits or turpentine to the consistency of shaving cream. The ground must be thin enough to work thoroughly into the weave of the canvas without leaving pronounced brushstrokes, but still be thick enough to maintain the integrity of the ground. The white ground should be applied after the Rabbit Skin Glue has dried for at least 24 hours. One to two coats are usually enough. The ground must cure for at least two weeks before applying oil color.

Rabbit Skin Glue and PVA sizing are used to coat the raw fibers of the painting support to prevent oil from causing rot. It serves as an isolating layer when using fabric supports. Size is traditionally made from a mixture of water and dried Rabbit Skin Glue, which is heated in a double boiler over low heat. Rabbit Skin Glue is an animal hide glue used to size fabric supports where traditional gesso, oil-based gesso, and oil paints are to be used. Rabbit Skin Glue is also a good binder for making traditional gesso, for use with gilding, and for adhering paper or canvas to virtually any support material such as wood. PVA is a more contemporary size, which is used to seal fabric supports before oil-based grounds and oil paints are applied.

Acrylic gesso is the most commonly used primer for either oil or acrylic colors. Acrylic gesso is not a true gesso but is generally referred to as such. It is best used as a ground for use with acrylic paints, as both the paint and ground are flexible when dry and contain polymer binders that make for good adhesion. Acrylic gesso can be used as a ground for oil paints but it is recommended that at least 3-4 coats be applied to the surface to ensure that the oil does not leach through. Some conservationists, however, would argue that acrylic gesso is not an ideal ground for oil paints due to the inflexibility of fully cured oils over the more flexible surface of an acrylic ground. Nevertheless, acrylic gesso is the most convenient ground available and is widely used by many artists for both mediums. It is a great all-purpose primer that will stick to almost any surface that is free of oil, grease, or dirt. It dries quickly to a very strong and flexible surface that will not crack or become brittle. Acrylic gesso is non-toxic, safe, and easy to use.

• Additives: Are generally used to bulk up paint and to alter the consistency of oil colors.
• Acrylic Polymer: The medium used as a binder in the production of acrylic paints.
• Acrylic Gesso (Primer): Canvas should not be sized if using an acrylic-based primer. The canvas should be primed with at least three coats if you intend to use oil colors. Dries quicker than oil-based grounds and can generally be used within 24 hours.
• Alkyd: Is a fast-drying oil-modified alkyd resin that is used to make alkyd oil colors or is used as a medium on its own to mix with traditional oil colors.
• Barrier Cream: A hand cream used to protect your hands from exposure to solvents and oils. It makes it easier to clean hard-to-remove oil paints from your hands.
• Compliments: Opposites on the color wheel, i.e., blue and orange are complementary. They consist of one primary (blue) and one secondary (orange) color. One is warm and the other is cool.
• Damar/Damar: Resin crystals that form from the sap tapped from the damar fir tree in Indonesia and Malaysia. Damar is used to make traditional varnishes for oil paintings.
• Drying Oils: Most vegetable-based oils, by themselves or when mixed with additives, will dry to form a tough film and binder for oil paint.
• Fat: All painting mediums are considered fat. Artist grade oil paints that dry shiny are generally fat.
• Fugitive: An impermanent color or pigment that is not lightfast.
• Gel: A medium used to alter the consistency of oil colors to a thicker gel consistency.
• Genuine Pigment: A true pigment that is derived from organic or inorganic material.
• Gesso: Traditional gesso is made of a white painting ground made from chalk, white pigment, glue, and water. True gesso is best applied to a rigid surface such as unfinished wood or masonite panel as it is too brittle for fabric supports. Contemporary methods have developed a "gesso" which can be used on canvas and is similar to a white acrylic or latex paint rather than a painting ground.
• Glazing: A technique that involves layering a series of transparent colors to create rich colors and depth. Oil color glazes are generally made with linseed oil or a faster-drying alkyd medium and a small quantity of color to achieve this effect.
• Ground: The surface to which the paint is applied after it has been sized or treated for painting.
• Hue: The actual color of a material, or its color name, i.e., turquoise or blue-green.
• Impasto: An oil painting technique that involves building up layers of thick paint. Each layer should be allowed to dry before applying the next in order to avoid cracking.
• Inorganic Pigments: These colors are mined directly from the earth (e.g., ochre, umber). They are generally quite heavy in weight and opaque in color.
• Lean: Painting mediums thinned with solvents are considered to be lean. Artist grade oil colors that dry matte are generally lean.
• Lightfastness: A term applied to pigments to describe their ability to resist fading with continued exposure to sunlight. If a color is lightfast, it is considered to be permanent.
• Linseed Oil: Is pressed from flax seeds. It is extracted by either cold or hot-pressed methods to produce oil with differing properties. It is also available in a more refined form for painting purposes.
• Medium: A solution added to paint to alter or enhance its properties. Mediums can alter drying time, improve and control flow, and add texture, among other things.
• Monoprinting: Printmaking method that uses either oil or water-based mediums to produce one-of-a-kind prints.
• Oil Paint: Composed of pigment particles suspended in an oil binder.
• Oil-based Ground: If being applied to a canvas support, the canvas should be sized first with either rabbit skin glue or PVA size. Can be applied directly to board. Needs 2 weeks to cure before oil color can be applied.
• PVA: Polyvinyl acetate is an adhesive or sizing agent used to seal fabric supports before oil-based grounds are applied.
• Rabbit Skin Glue: A traditional sizing used to prepare canvas for painting. It provides a barrier between the canvas and the oil paint to prevent the oil from rotting the canvas.
• Saturation: The degree of intensity of a color or hue.