Mineral spirits is a clear, petroleum-derived solvent widely used in professional and household settings. Known as white spirit or paint thinner, its primary function is to thin oil-based paints and varnishes or to clean tools and equipment. Because it is a hydrocarbon-based liquid, it behaves differently from water when exposed to low temperatures. Under typical environmental conditions, mineral spirits does not solidify.
The Extremely Low Freezing Point
The reason mineral spirits resists freezing is rooted in its chemical composition, which is a complex mixture of various aliphatic and alicyclic hydrocarbons. This blend of different-sized molecules disrupts the orderly arrangement required for a solid crystalline structure to form. True solidification, or freezing, only occurs at temperatures rarely encountered outside of specialized laboratory or extreme Arctic environments.
Commercial-grade mineral spirits typically has a freezing point far below zero, often cited around \(-74\) degrees Fahrenheit (\(-59\) degrees Celsius). Some formulations may be even lower, with certain specifications listing the freezing point at \(-105\) degrees Fahrenheit (\(-76\) degrees Celsius). The wide range of freezing points, sometimes as high as \(-13\) degrees Fahrenheit, reflects the slight variations in the hydrocarbon blend used by different manufacturers.
Viscosity Changes and Gelling
Long before reaching the actual freezing point, a more common and noticeable change occurs when mineral spirits is exposed to cold temperatures. Like most liquids, its viscosity increases dramatically as the temperature drops. The liquid thickens and flows much more slowly, a process often mistakenly referred to by users as “freezing” or “gelling.”
This thickening effect becomes apparent even at temperatures near \(32\) degrees Fahrenheit (\(0\) degrees Celsius), making the solvent impractical for its intended use. The material may become cloudy, sludgy, and too viscous to effectively thin paint or clean brushes. This state of reduced fluidity is a physical change, not a chemical one. The thickening is caused by the reduced energy and movement of the molecules, which increases the internal friction and resistance to flow.
Storage and Handling in Cold Climates
The most effective way to prevent mineral spirits from becoming overly viscous is to store it in a temperature-controlled environment. The ideal solution is to keep the containers in a cool, dry place where the temperature remains above freezing. This simple measure ensures the solvent maintains its intended fluidity and is ready for use when needed.
If the mineral spirits has already thickened, it can be easily restored to its liquid state by warming it up. The safest approach is to move the container to a warmer location, such as a heated garage or indoors, and allow it to return to room temperature slowly. Mineral spirits is a flammable liquid, with a flash point often around \(100\) to \(111\) degrees Fahrenheit. Therefore, direct heat sources, open flames, or placing the container near a furnace should never be used to speed up the warming process.