Petroleum Distillates in Woodworking

Solvents for woodworking have gotten confusing as the range of finishing products has expanded and safety regulations have changed what’s available in some formulations. As someone who has worked with finishes for decades and had to learn which solvent does what from a combination of experience and hard-won mistakes, I want to give you a clear guide to the petroleum-based solvents that woodworkers encounter most often — what each one is, what it’s for, and how to use it safely.

Mineral Spirits

Mineral spirits — also sold as Stoddard solvent, white spirits, or paint thinner — is the most versatile petroleum solvent in a woodworking shop. It’s a relatively slow-evaporating solvent that’s used as a thinner for oil-based paints, varnishes, and alkyd finishes; as a cleanup solvent for oil-based products; and as a general degreaser for wood surfaces before finishing.

Mineral spirits comes in regular and odorless formulations. Regular mineral spirits has a strong petroleum odor that dissipates as it dries. Odorless mineral spirits (OMS) has had the aromatic compounds removed, producing a much less offensive smell. Both work the same way chemically; OMS is simply more pleasant to use indoors. OMS costs more but the increased comfort for indoor finishing work is usually worth it.

For woodworking specifically, mineral spirits is commonly used to “pop” the grain before applying oil finishes — wiping the surface with mineral spirits shows you what the wood will look like under an oil finish before you commit. It evaporates without raising the grain or leaving a residue (if you let it flash off completely before applying finish — typically 15-30 minutes).

Naphtha (VM&P Naphtha)

Naphtha — the full name is VM&P Naphtha, standing for “varnish makers and painters” — is a faster-evaporating petroleum solvent than mineral spirits. It’s used in situations where you want the carrying solvent to leave quickly: thinning shellac-based products, cleaning and degreasing immediately before finishing (the fast evaporation means the surface is dry for finish application within minutes), and thinning wiping varnish for faster application.

Naphtha is more aggressive in evaporation than mineral spirits but less aggressive than acetone or lacquer thinner. This puts it in a useful middle range for many woodworking applications. It’s also an excellent choice for removing wax from a wood surface before applying a new finish — wax contamination is one of the most common causes of adhesion failures in finish work, and naphtha dissolves wax cleanly without leaving residue.

The faster evaporation means higher fire risk than mineral spirits — the flash point of naphtha is lower. Ventilation and no ignition sources in the working area are important safety requirements.

Turpentine

Turpentine — genuine gum turpentine, derived from pine resin — is a traditional wood finishing solvent that’s been largely replaced by petroleum solvents in modern practice but remains relevant for specific applications. It’s a better solvent for traditional oil-based products than mineral spirits and has been used in oil finishes and traditional varnishes for centuries. The smell is distinctive and, to most woodworkers, not unpleasant — it’s the smell associated with the oil-finished furniture of earlier centuries.

Pure gum spirits of turpentine is still available from finishing suppliers. For traditional oil varnish recipes and for woodworkers who prefer to work with historically consistent materials, turpentine remains the solvent of choice. For everyday oil-based finish thinning, mineral spirits is equivalent and less expensive.

Lacquer Thinner

Lacquer thinner is not a single chemical but a blend of fast-evaporating solvents — acetone, toluene, xylene, methyl ethyl ketone, and others depending on the specific formulation. It’s used primarily to thin nitrocellulose lacquer (and other lacquers compatible with solvent thinning), to clean lacquer spray equipment, and to strip dried lacquer from surfaces and equipment.

Lacquer thinner evaporates very quickly — faster than naphtha, much faster than mineral spirits. This makes it useful for cleaning spray guns and equipment where a slow-evaporating cleaner would leave residue in fine passages. It’s also useful for spot-cleaning lacquer drips or runs before they fully harden.

Lacquer thinner is aggressive — it will dissolve most oil-based and shellac-based finishes as well as lacquer, and it will damage plastics. Use with appropriate PPE (nitrile gloves, safety glasses, organic vapor respirator) and in well-ventilated areas only. The flash point is low and the vapors are heavier than air, meaning they can accumulate at floor level where ignition sources might be.

Denatured Alcohol

Denatured alcohol — ethanol with denaturants added to make it undrinkable — is the solvent and thinner for shellac. It’s also used as a general cleaner for wood surfaces before finishing, particularly for removing contaminants that mineral spirits won’t dissolve. Denatured alcohol dries quickly, raises wood grain moderately (less than water, more than mineral spirits), and leaves no residue.

For shellac application, the ratio of shellac flakes to denatured alcohol determines the cut (concentration) of the solution. A two-pound cut — two pounds of shellac flakes dissolved in one gallon of alcohol — is the standard reference for shellac mixing, and most premixed shellac products are sold in cuts relative to this standard.

Safe Storage and Handling

All petroleum solvents are flammable. Store in their original containers in a cool, away-from-heat location. In a shop with any heat source — wood stove, forced air furnace, water heater — keep solvents in a metal safety cabinet. Oily and solvent-soaked rags are a serious spontaneous combustion risk; spread them flat outside to dry before disposing in a metal lidded container. These fire safety practices are not theoretical — solvent-soaked rag fires have destroyed many shops over the years.