Turpentine vs Other Solvents

Solvents in oil painting have a bad name. That is, many fear that sovents are significantly toxic, harmful, or explosive. For some years there has been a movement of painters who try to avoid or reduce their uses of solvents while painting. But for those who use solvents, here is a list of the various solvents available and a few notes on their usage.

"Upstream, Druid Hill Creek," oil on panel, 2020

Turpentine 

The traditionally used solvent in oil painting is known as "turpentine," but in fact is a product distilled from turpentine, known as "rectified turpentine." Turpentine is actually the resinous sap of a specific kind of tree, many in the Pinus species. The sap is distilled, or rectified, producing a clear to yellow liquid that is used to thin oil paint, make varnishes and mediums for painting, and in various chemical processes. Rectified turpentine is a complex substance with a slightly oily but scanty residue. 

 

Oil of Spike Lavender

A traditional solvent derived from the spike lavender plant (Lavandula spica) and is said to have been used by masters of the past in thinning their oils. It is often listed as an essential oil. Colloquially known as "oil of spike," it's used mostly as a component of various painting mediums along with oil and a resin of one kind or another. Because of scarcity and expense oil of spike is rarely used as a simple solvent.

Mineral Spirits

Mineral spirits are solvents derived from crude oil. Sometimes called "white spirit," especially in Britain, mineral spirits come in smelly and odorless forms. The odorless form is sold by several companies under various brand names but in general comprises straight-chain hydrocarbons (C7-C13), while the smellier variety contains "aromatics" or ring compounds too. These solvents have many industrial applications as well as finding use in oil painting. (Brand names include Gamsol, Turpenoid, and others.)

"Downstream, Druid Hill Creek," oil on panel, 2020

Suggestions for using solvents:

• Buy high quality solvents. Typical hardware store turpentine is not suitable for artwork. Odorless mineral spirits are similar to one another regardless of brand names but artist-grade spirits are more likely to be high quality.
  
• Ventilate your studio well. Solvents evaporate but will remain in still studio air. An open window is the minimum ventilation but an exhaust fan is optimum. Keep your solvent container covered unless it's a very small cup.
• Use the least solvent necessary. Overuse of solvent can result in paint with less oil binder per unit volume so that the resultant paint film will be more fragile or "underbound." Using the least solvent also releases less into the atmosphere.
• Dispose of used solvent (brush washing jars, etc) responsibly. Mineral spirits are polluting. 
• In general, citrus-based solvents are only useful for cleaning brushes.