(Excerpts from ART HARDWARE: The Definitive Guide to Artists’ Materials, by Steven Saitzyk © 1987)
Thinners, Diluents, or Solvents
are used in painting primarily to thin the paint or medium, and should then evaporate from the paint film without leaving a trace. The next most important function of thinners such as turpentine is to clean tools and brushes. Keep these two principles in mind as you read the following descriptions of the various solvents.
Many thinners and solvents can be hazardous to health. They are not only inhaled and ingested, but are absorbed directly through the skin.
Gum Turpentine is made from distilling the resinous gum from pine trees. Gum turpentine usually contains a small amount of sticky residue, which can be imparted to a painting if this kind of turpentine is used in large quantities. It may remain in the layers of paint, inhibiting proper drying and, in time, causing discoloration. Unless cost is a serious consideration, I do not recommend using gum turpentine with artist-grade paints and media. It is, however, perfectly acceptable for cleaning tools and brushes.
Rectified, or Artist-Grade, Turpentine
Rectified, or Artist-Grade, Turpentine is double distilled to remove the last bit of residue from the pine-tree gum. This thinner is ideal for oil paints and media because it does the job and then evaporates from the paint film without a trace. Artists often buy the finest paints and media and then use the cheapest thinners. This is like buying a Rolls Royce and putting kerosene in the gas tank. There are areas where compromises can be made, but they should be made with common sense.
Venice Turpentine is a resin used as a thickening agent in the preparation of media and is not a solvent or thinner.
Petroleum Distillate, Mineral Spirits, and White Spirits
Petroleum Distillate, Mineral Spirits, and White Spirits are byproducts from the manufacture and refinement of petroleum. Although they are all basically the same type of product, the actual chemical composition may differ vastly from brand to brand. This is of little concern when purchasing a product made for artists’ paint such as a turpentine substitute. There can be a serious problem, however, if this solvent is used with house paints or if house paint mineral spirit thinners are used with artists’ materials. Always test a solvent with a particular paint no matter what the label says.
The advantage of using petroleum distillates that are produced for artistic use is that they are less expensive than turpentine, have a longer shelf life, leave no sticky residue, and according to government standards, are less hazardous than turpentine. They are also recommended for painters who are allergic to turpentine. There are, however, two drawbacks. The first is that dammar and mastic are partially insoluble in these solvents. The other is that they have a decidedly oily smell, which some people may find offensive.
Odorless Paint Thinners
Odorless Paint Thinners are essentially the same as petroleum distillate or mineral spirits except that the unpleasant odor has been removed or masked. All are fine turpentine substitutes if you avoid using them with dammar or mastic.
Remember, however, that the paint thinner that is sold in hardware stores is not the same, and may contain other solvents that can destroy an artist-grade paint, ruin brushes, substantially increase health risks, or cause other dangerous or unpredictable results. One artist reports that she was using a paint thinner purchased at a hardware store, when all of a sudden the hairs were falling out of her brushes in clumps. She had been using hardware-store paint thinner without serious problems until this incident. After investigation, it was discovered that many of the solvents packaged for hardware stores under the name “paint thinner” may be changed by the manufacturer without notice. These changes may be perfectly satisfactory for hardware use, but in this case the last batch of paint thinner the artist purchased was, unfortunately, particularly good at dissolving the glues used to hold her brushes together.
Oil Spike of Lavender
Oil Spike of Lavender is one of the oldest known turpentine substitutes. It is the essential oil from the lavender plant and possesses a most wonderful scent. It evaporates more slowly than turpentine, is nonflammable, and is primarily used as a turpentine substitute by those who are allergic to turpentine. Since it is slower drying than turpentine, it is occasionally used to slow the drying time of oil paint. Its disadvantages are its extremely high cost and limited availability. Currently, the only sources of this product are Winsor & Newton, Sennelier, and Schmincke.