What are mineral spirits? (with photos)

Mineral alcohol is often used as a thinner.

Seasoned paint professionals today use a solvent called mineral turpentine as an alternative to turpentine to thin paints and clean brushes. Mineral spirits is a mild, low-volatility petroleum distillate that can be used for degreasing and cleaning machines and, together with cutting oil, as a lubricant for cutting and reaming screw threads.

A clean brush with mineral spirits.

Mineral spirit is also known as Stoddard solvent, referring to its co-inventor, WJ Stoddard. In 1928, Stoddard, along with Lloyd Jackson, developed this alternative solvent for use in their dry cleaning business. Stoddard solvent remained the most popular dry cleaning solvent in America during the 1950s and the term is used most often in this context. Outside the United States and Canada, mineral spirits are called white spirits, although they are actually a clear liquid.

Mineral alcohol is used in the production of asphalt.

In the distillation process, chemicals such as aliphatic (paraffin) and (cyclo-alicyclic propane) hydrocarbons are combined with aromatic alkyl groups (benzene) hydrocarbons to produce the three most common types of mineral spirits. Type I underwent hydro-desulfurization, where most of the sulfur is removed from the distillate. Type II is basically a solvent extraction, where hydrotreatment removes most of the aromatic hydrocarbons. Type III is processed with hydrogenation, addition of hydrogen. What this all means is that the atomic structure of the various hydrocarbons that make up the distillate of each type of mineral alcohol has been switched for different applications.

Type II odorless mineral alcohol is one of the most common types of thinner. It has been treated to remove aromatic solvents, allowing its use in the manufacture of low-odor oil-based paints. Mineral spirit in its aromatic form is, among other uses, a basic ingredient in the production of asphalt.

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In addition to typing, mineral alcohols are categorized as class 1, 2 or 3. Class 1 is a product with a high flash point or burning temperature and therefore a low volatility rating. Class 2 has a slightly lower flash point temperature and class 3 the highest volatility with obviously the lowest flash point of the three classes.

Although mineral spirits are one of the safest alternative cleansers and solvents, it is described by the Occupational Safety and Health Administration (OSHA) as a mild skin irritant. It also receives a class 3 flammability rating; once its relatively high flash point is reached, mineral spirits will burn like any hydrocarbon based solvent, emitting dangerous toxins. In addition, chronic toxic encephalopathy, a brain disease often found in commercial and residential painters, has been attributed to prolonged exposure to mineral spirits. Therefore, while mineral spirits are a much safer alternative to many solvents in certain applications, it must, like any petroleum distillate, be stored and handled with care.

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