Misplaced Pages

Revision as of 05:34, 19 June 2011

Oil paint is a type of slow-drying paint that consists of particles of pigment suspended in a drying oil, commonly linseed oil. The viscosity of the paint may be modified by the addition of a solvent such as turpentine or white spirit, and varnish may be added to increase the glossiness of the dried film. Oil paints have been used in Europe since the 12th century for simple decoration, but were not widely adopted as an artistic medium until the early 15th century. Common modern applications of oil paint are in finishing and protection of wood in buildings and exposed metal structures such as ships and bridges. Its hard-wearing properties and luminous colors make it desirable for both interior and exterior use on wood and metal. Due to its slow-drying properties, it has recently been used in paint-on-glass animation. Thickness of coat has considerable bearing on time required for drying: thin coats of oil paint dry relatively quickly.

History

The technical history of the introduction and development of oil paint, and the date of introduction of various additives (driers, thinners) is still - despite intense research since the mid 18th century - not well understood. The literature abounds with incorrect theories and information: in general, anything published before 1952 is to be treated with extreme scepticism.

The slow-drying properties of organic oils were commonly known to early painters. However, the difficulty in acquiring and working the materials meant that they were rarely used (and indeed the slow drying was seen as a disadvantage). As public preference for realism increased, however, the quick-drying tempera paints became insufficient. Flemish artists combined tempera and oil painting during the 15th century, but by the 17th century easel painting in pure oils was common, using much the same techniques and materials found today.

The oldest known extant oil paintings date from 650 A.D., found in 2008 in caves in Afghanistan's Bamiyan Valley, "using walnut and poppy seed oils." Though the ancient Mediterranean civilizations of Greece, Rome, and Egypt used vegetable oils, there is little evidence to indicate their use as media in painting. Indeed, linseed oil was not used as a medium because of its tendency to dry very slowly, darken, and crack, unlike mastic and wax.

Greek writers such as Aetius Amidenus recorded recipes involving the use of oils for drying, such as walnut, poppy, hempseed, pine nut, castor, and linseed. When thickened, the oils became resinous and could be used as varnish to seal and protect paintings from water. Additionally, when yellow pigment was added to oil, it could be spread over tin foil as a less expensive alternative to gold leaf. Early Christian monks maintained these records and used the techniques in their own artworks. Theophilus Presbyter, a 12th century German monk, recommended linseed oil but advocated against the use of olive oil due to its long drying time.

In the 13th century, oil was used to detail tempera paintings. In the 14th century, Cennino Cennini presented a painting technique utilizing tempera painting covered by light layers of oil.

It is commonly stated and believed (although the evidence for this is extremely questionable) that today's technique of oil painting was created circa 1410 by Jan van Eyck. Though van Eyck was not the first to use oil paint, he was the first artist to have produced a siccative oil mixture which could be used to combine mineral pigments. Van Eyck’s mixture may have consisted of piled glass, calcined bones, and mineral pigments boiled in linseed oil until reaching a viscous state. Or he may have simply used Sun-thickened oils (slightly oxidized by Sun exposure). He left no written statement.

Antonello da Messina later improved oil paint: he added litharge, or lead (II) oxide. The new mixture had a honey-like consistency and increased drying properties. This mixture was known as oglio cotto—"cooked oil."

Leonardo da Vinci later improved these techniques by cooking the mixture at a very low temperature and adding 5 to 10% beeswax, which prevented darkening of the paint. Giorgione, Titian, and Tintoretto each may have altered this recipe for their own purposes.

The use of any cooked oils or Litharge (sugar of Lead) will darken an oil painting rapidly. None of the old Masters whose work survives used these in their paintings. Both ingredients became popular in the 19th century.

Since that time, experiments to improve paint and coatings have been conducted with other oils. Modern oil paints are created from bladderpod, ironweed, calendula and sandmat, plants used to increase the resistance or to reduce the drying time.

Paint tube

The paint tube was invented in 1841, superseding pig bladders and glass syringes as the primary tool of paint transport. Artists, or their assistants, previously ground each pigment by hand, carefully mixing the binding oil in the proper proportions. Paints could now be produced in bulk and sold in tin tubes with a cap. The cap could be screwed back on and the paints preserved for future use, providing flexibility and efficiency to painting outdoors. The manufactured paints had a balanced consistency that the artist could thin with oil, turpentine, or other mediums.

Paint in tubes also changed the way some artists approached painting. The artist Pierre-Auguste Renoir said, “Without tubes of paint, there would have been no Impressionism.” For the Impressionists, tubed paints offered an easily accessible variety of colors for their plein air palettes, motivating them to make spontaneous color choices. With greater quantities of preserved paint, they were able to apply paint more thickly.

Many modern paint manufacturers test for lightfastness, how well a pigment retains its color when exposed to light. The results of these tests are printed on the paint tube's label, often on the back with the pigment list.

Artists can also buy empty tubes and fill them with paint. The filling is done through the bottom. Then the bottom is folded and crimped. Paint for later use is accessed through the screw cap at the other end — as usual. This can be useful for having on hand a mixed color that is found to be a good starting point for mixing a color within a commonly used range, as concerns an artist's personal preferences.

Practical properties of oil paint

Many artists today consider oil painting to be the fundamental art medium; something that a student should learn to appreciate, because of its properties and use in previous, very popular artwork. Typical qualities of oil paint include a long "open time," which means that the paint does not dry quickly. Oil paints take several weeks to dry, this allows the artist to work on a painting for many sessions. Oil paint also has a propensity to blend into surrounding paint allowing very subtle blending of colors. This medium also produced vivid color with a natural sheen and distinct contrast. Oil paints have a surface translucency similar to human skin, making it an ideal medium for portraits.

Carrier

Traditional oil paints require an oil that will gradually harden, forming a stable, impermeable film. Such oils are called siccative, or drying, oils, and are characterized by high levels of polyunsaturated fatty acids. One common measure of the siccative property of oils is iodine number, the number of grams of iodine one hundred grams of oil can absorb. Oils with an iodine number greater than 130 are considered drying, those with an iodine number of 115-130 are semi-drying, and those with an iodine number of less than 115 are non-drying. Linseed oil, the most prevalent vehicle for artists' oil paints, is a drying oil.

When exposed to air, oils do not undergo the same evaporative process that water does. Instead, they oxidize into a dry solid. Depending upon the source, this process can be very slow, resulting in paints with an extended drying time.

The earliest and still most commonly used vehicle is linseed oil, pressed from the seed of the flax plant. Modern processes use heat or steam in order to produce refined varieties of oil, which contain fewer impurities, but cold-pressed oils are still the favorite of many artists. Other vegetable oils such as Hemp, poppy seed, walnut, sunflower, safflower, and soybean oils may be used as alternatives to linseed oil for a variety of reasons. For example, safflower and poppy oils are paler than linseed oil and allow for more vibrant whites straight from the tube.

Once the oil is extracted additives are sometimes used to modify its chemical properties. In this way the paint can be made to dry more quickly if that is desired, or to have varying levels of gloss. Modern oils paints can, therefore, have complex chemical structures; for example, affecting resistance to UV or giving a suede like appearance.

Non-oil carriers

New carriers for paint were developed out of organic polymer technology in the 20th century. In many cases, such as acrylic paint, a different binder is substituted for oil. These new binders have different properties than oil paint, such as faster drying times and increased mechanical strength of the paint film. They require different (though overlapping) techniques and provide new possibilities that are not available to oil painters, such as the building of heavy texture and impasto, the use of collage, and the sculpting of the paint surface. Contemporary thinking therefore recognizes the new materials as separate media.

Some manufacturers, in an attempt to produce a medium that is oil-based but avoids toxic cleaners and thinners, have managed to produce water miscible oil paints. The vehicle for such paints is an oil with a surfactant molecule chemically bonded to it which allows oil to mix with water in much the same way dish soap does, but with greater sophistication. These paints still contain dryers and are by nature toxic.

Drying of oil paint

Unlike water-based paints, oils do not form films by evaporation. Instead drying oils function by the chemical process of oxidation, related generally 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 monomers polymerize, 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. The autoxidation entails attack by oxygen at what are called allylic sites (centres adjacent to a double bond). The result is a stable film which, while somewhat elastic, does not flow or deform under the pull of gravity.

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.

Pigment

The color of oil paint derives from the small particles mixed with the carrier. Common pigment types include mineral salts such as white oxides: lead, now most often replaced by less toxic zinc and titanium, and the red to yellow cadmium pigments. Another class consists of earth types, e.g. sienna or umber. Synthetic pigments are also now available. Natural pigments have the advantage of being well understood through centuries of use but synthetics have greatly increased the spectrum available, and many are tested well for their lightfastness.

Toxicity

Many of the historical pigments were dangerous, and many pigments still in popular use today are highly toxic. Many toxic pigments, such as Paris green (copper(II) acetoarsenite) and orpiment (arsenic sulfide), to name only two, have fallen from use. Some pigments still in use are toxic to some degree, however. Many of the reds and yellows are produced using cadmium, and vermilion red uses natural or synthetic mercuric sulfide or cinnabar. Flake white and Cremnitz white are made with basic lead carbonate. The cobalt colors, including cobalt blue and cerulean blue, are made with cobalt compounds. Some varieties of cobalt violet are made with cobalt arsenate. Manufacturers advise that care should be taken when using paints with these pigments, and advise never to spray apply toxic paints. Great misinformation abounds regarding the toxicity of oil paints, with many artists misinterpreting the "non-toxic" label on many paints to mean that the paint is actually non-toxic. According to United States regulations, the "non-toxic" label can be applied to any chemical substance for which no adequate tests have been preformed to determine toxicity; thus, the label "non-toxic" simply indicates a paint whose toxic properties have not been adequately researched and thus are unknown.

Zinc white and titanium white may carry a California health label for lead content. While those paints contain far less lead than the lead whites, lead in even minute quantities is a potent neurotoxin. Some manufacturers put the text "California only" above the warning.

Thinners such as turpentine and white spirit are flammable, carcinogenic, and can cause acute pulmonary distress. Some of them, particularly the poor grades of turpentine, have a strong odor, but even the more refined thinners such as odorless mineral spirits can be harmful to the health if used inappropriately. But because of the lack of adequate testing of these substances, the EPA has not made that determination, and no empirical evidence exists for this claim.

Generally speaking, individuals using these chemicals should assume responsibility for educating themselves about appropriate safety precautions and follow MSDS guidelines carefully. Solvents must be used in a well-ventilated area or acute chemical sensitivity can occur through over-exposure, and neither solvents nor oil paints should come into direct or prolonged contact with the skin.

See also

• Oil painting
• Drying oil
• Semi-drying oil
• Egg tempera
• Acrylic paint
• Watercolor
• Acrylic painting techniques

References

This article includes a list of general references, but it lacks sufficient corresponding inline citations. Please help to improve this article by introducing more precise citations. (March 2010) (Learn how and when to remove this message)

1. Coremans, Gettens, Thissen -La technique des Primitifs flamands- Studies in Conservation 1 (1952)
2. Theophilus Presbyter Book I ch. 25
3. "Oldest Oil Paintings Found in Afghanistan", Rosella Lorenzi, Discovery News. Feb. 19, 2008.
4. Callen, Anthea. The Art of Impressionsm: How Impressionism Changed the Art World. Yale University Press. 2000.
5. The Painter's Craft; Ralph Mayer; ISBN 978-0140468953
6. H. Gluck, "The Impermanences of Painting in Relation to Artists' Materials", Journal of the Royal Society of Arts, Volume CXII 1964

General

• Mayer, Ralph. The Artist's Handbook of Materials and Techniques Viking Adult; 5th revised and updated edition, 1991. ISBN 0-670-83701-6

History

• "History of Oil Paint." Cyberlipid Center.

• "History of Painting Mediums." Real Color Wheel.

• "A Brief History." Sanders-Studios.com.

• "The Evolution of Oil Color." Daniel Smith Artists' Materials.

Chemistry of Oil Paint

• “Autoxidation.” McGraw Hill Encyclopedia. 8th ed. 1997.
• Flanders, Peggy J., How Oils Dry, 5 May 2006.

• Friedman, Ann, et al., Painting, World Book online, 46 Stetson St. #5 Brookline, MA. 10 May 2006.
• History of Oil Paint, CyberLipid.org, 5 May 2006.

• Mecklenburg, Marion, Autoxidation of Oil, 13 Jan 2006. The Painter's Handbook, Mark David Gottsegen. 11 June 2006.

• van den Berg, Jorit D.J., Template:PDFlink, MOLART 2002. 8 May 2006

• Paints
• Oils