Basics of oil painting: Mediums Part 3. Solvents

Solvents/Diluents are being used to thin the paint (independently or in mixtures with oil and lacquer) and for the supporting needs like cleaning palettes and brushes.

Solvents evaporate quickly and completely as the oil paint dries, it is their most significant difference from the drying oils (we were discussing them in the previous article about mediums here).

2 types of solvents are being used in oil painting: natural hydrocarbons (turpentines) and petroleum origin hydrocarbons (white-spirit).

Turpentine by Daler-Rowney

Turpentine

- is the traditional solvent used in oil painting, usually made from the sap of pine trees. Has a fast evaporation rate.

It was used almost universally until Odorless Mineral Spirits were created. However, it has a huge minus – it is dangerous. Many people are allergic to the odor and touch, it may cause lung and central nervous system damage when inhaled, and skin rash if touched.

Other names: spirit of turpentine, oil of turpentine, genuine turpentine, English turpentine, distilled turpentine, double rectified turpentine, or simply turps. Turp should not be confused with Venetian (Venice) Turpentine.

Venice/Venetian Turpentine by Sennelier

Venice turpentine

- is derived from European larch trees. Venice turpentine has unique lustre as well as honey-like consistency, dries slowly. It has been used in the past to isolate incompatible pigments (such as lead white and Vermillion).

It is also a classical additive for glazing – it increases the flow and transparency, adds gloss to glazing layers in oil colour, cause the glazes to melt into one another, and also cause the edges of the painted areas to bleed slightly into their surroundings, creating soft edges. Needs to be diluted with turpentine.

It seems that Venice turpentine is a good medium for creating Sfumato effect.
Detail of the painting by Bernardino Luini - Saint Catherine (early 16th century) 

Mineral spirits/White spirits

Bottles are similar, but the smell is very different

- is based on petroleum and has a moderate evaporation rate, releasing harmful vapors. Mineral spirits is less expensive than turpentine, but Odorless Mineral Spirits are more expensive. Since some of the harmful aromatic solvents were removed, classic mineral spirit is a stronger solvent, than odorless variant. The more the spirits are refined (removal of aromatic compounds), the safer the product becomes.

Volatile/Essential oils

- are also being used as an oil paint diluent. An essential oil is a liquid that is generally distilled (most frequently by steam or water) from the leaves, stems, flowers, bark, roots, or other elements of a plant. Essential oils slows the drying time of oil paint, because they evaporate only partly and mainly oxidized by oxygen in the air.

Price for the 55ml bottle of Spike Lavender Oil is 33$
while turpentine costs around 8$ for 75ml bottle  

Oil of Spike Lavender

- is the most popular essential oil. It is a fluid colorless or yellow-green liquid with a smell of fresh lavender flowers with a hint of wood.

Lavender Oil characteristics are similar to Turpentine, but artists use it rarely because of the high price. However, it is becoming more popular since it is non-toxic.

Tip

- Try to use only artist' quality turpentine. It is considered that the industrial solvents you can find in hardware stores may contain impurities. Anyway, you can use an industrial variety, but firstly do this test: Put 1-2 drops on white paper and let them evaporate. If the the solvent doesn't leave any trace or smell – it is good enough for oil painting. Sometimes the solvent leaves a halo, which means that it is not purified and it may cause strong yellowing or blackening of the painting.

Caution

- It is essential to use solvents in a well-ventilated room
- Do not forget that thinners are flammable and toxic!