Linseed oil based artists’ paints do not contain solvents.

Solvents are used in an oil painting process to defat (“bite”) and slightly open an oil paint layer to increase the adhesion between layers.  Too much solvent breaks down the linseed oil binder and decreases adhesion.  Also solvents are used to thin paints for easier spreading; to dissolve resins to make painting mediums; and for brush and studio clean up. 

Do you HAVE to use solvents in oil painting?  No.  (discussion)

Nature provides solvents.  Humans refine them.  Obviously we started with making hooch.  Alcohol is a solvent which dissolves fatty acids, sugars and many vegetable alkaloids into solution.  

When an overripe apple is cut, a “sharp” smell is released from the sweet. Alcohol is made through a fermentation process during which sugar from carbohydrates (grain and fruit) is converted into alcohol by yeast.  Humans beings have controlled fermentation processes since the cave times. The evidence is in the residue from beer (prehistoric) and wine (approx. 8000 BCE) left behind in the bottom of cups unearthed by archeologists. Beer and wine are fermented drinks, not distilled.  

Ancients probably distilled wine and beer for the same reasons we do - to concentrate flavors and increase the alcohol content. 

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Distillation is basic steam collection. Wine, for example, is heated in a covered pot until ethyl alcohol evaporates (about 175 degrees F).  The steam is then collected through tubes connected to cover then cooled.  After distillation, alcohol is fluid at room temperature. There are three basic types of alcohol: isopropyl, methyl, and ethyl.

Ethyl alcohol is ethanol, the only type of alcohol which humans can consume without harm.  “Sura” made in India between 3000 - 2000 BCE is considered the first cocktail distilled from rice.  800 BCE Chinese mixologists distilled various concentrations of ethanol from rice. The Babylonians worshiped a wine goddess about 2700 BCE.  The Greeks preferred mead; the Romans wine.

Vinegar is “poor man’s wine” - posca, often carried by Roman legionnaires into battle.  Stale wine, decomposing fruits and other carbohydrades are fermented by the action of acetic acid bacteria.  Acetic acid bacteria are airborne and ubiquitous in nature.  In warm climates, vinegar was widely available and a good cleanser.

To clean industrial operations using grease and oil, stronger solvents were distilled from tree sap especially pine trees and some oaks.  Oil of turpentine is harvested more like maple syrup moving very slowly from cuts in pine trees’ bark.  The resin is distilled and the volatile components of the resin are collected as “spirits of turpentine.” The best quality then and now is double or triple distilled and water clear. (“Cheap turps” contains approx 20% resin debris just don’t use.)

While the best alternative at the time, turpentine is a toxic work place hazard.  Turpentine has a dangerously low flash point (100 degrees F.) and a dangerously low permissible exposure level (PEL) which means turpentine evaporates very rapidly and fills the air with aromatic fumes.  Industry has produced far less toxic and cheaper solvents from petroleum distillates, “mineral spirits”, since WWII.  Increasingly better qualities of odorless mineral spirits (OMS) have been introduced since the 1970s. 

Until the advent of mineral spirits, turpentine was the common solvent used in painters’ studios to make paints more fluid; to make spirit varnishes and for clean up.

Turpentine was distilled in the ancient Mediterranean and anywhere pine trees grow.  It is a strong solvent (Kb value 56) which was probably on the shelf of most workshops, including book illustrators and binders, stained glass and metal workers, blacksmiths and kilns.  Except for a dash of alcohol in egg tempera, solvents were generally not needed among the art materials used to make opaque media like mosaics and murals. 

Things changed in the 15thC. Everybody wanted to make art works with the radical new concepts inspired by Florentine architect Brunelleschi (1377-1446).  He reinvented the principles of linear perspective lost since Classical times.  He demonstrated how to draw and paint images on to 2D  surfaces and create 3D illusions of space.  These new ideas forced painters to reconsider their opaque mural making  materials including muted earth pigments, gesso and lime plaster.  Creating illusions of space required a more transparent painting media to reveal the narrative.  

Initially painters experimented with adding linseed oil to egg tempera paints. Refined linseed oil was used for medicine and in cooking. The quality used in medicine was probably more aromatic but similar to the cold pressed linseed oil you can buy from health food stores today, probably just as expensive. But changing the binder was not enough. While adding linseed oil increased transparency, the paints were oily and slow drying to an uneven sheen. There was a missing ingredient.

Maybe a varnish was needed to saturate dried colors and unify the surface?  Also would adding varnish into paint layers toughen up the surface?  For answers, painters probably looked to industries which produced “oil varnishes” from natural resins. Copal and mastic among other resins are too hard to dissolve in solvent.  To make oil varnishes, resins had to be boiled into raw linseed oil until they melted and dissolved.  The long, hot process resulted in dark, dense coatings which were unsuitable for creating transparency.  

During the Age of Discovery, Portuguese sailors returned from East Asia with bags full of damar resin. Soft damar resin dissolved in common turpentine without heat. The resulting “spirit” varnishes were transparent. By mid 15thC, various mixtures of spirit varnish, linseed oil and colorants formed a system that became the foundation of painting until Impressionism.

Since WWII solvents made from petroleum distillates, a group of solvents distilled from crude oil, have replaced turpentine in industrial work places. Mineral spirits (MS) and odorless mineral spirits (OMS) are not absorbed into healthy unbroken skin.  MS does have a high aromatic component. 

Ironically - now that oil painters have access to an even safer OMS solvent, they are worried because they CAN’T smell it!  

You cannot smell the aromatic fumes because they have been refined out of the solvent to reduce exposure.  The aliphatic components of the solvent evaporate much slower so you can work around the solvent longer.

For those who want to work again with oil paints or those curious to try:

Managing solvents is the key to a successful oil painting practice.

Best choice:  Odorless mineral spirits (OMS) is petroleum distillates, a group of hydrocarbon-based chemicals that are refined from crude oil.  Use with alkyd resin painting medium instead of natural resin mediums.

OMS is strong enough to defat oil paints; thin alkyd resin painting mediums and for brush and studio clean up.  OMS is barely strong enough to dissolve damar resin - partially.  The resulting solution will be cloudy, fine for general painting but don’t use for transparent glazes.  

No odor.  Aromatic components removed.

Permissible exposure level (PEL) 300 (Higher PEL = safer.  Over 300 solvent may not be strong enough to defat oil colors). Keep containers closed.

Flashpoint  approx.  145 degrees F.  (Higher flashpoint = safer)

Kb Value 28 - solvent power LOW   (compare to turpentine Kb 56)

OMS is odorless because the aromatic components have been removed.  If there is any odor, buy a better quality.  

Mineral spirits (MS) - do not use.  Aromatic components can become too highly concentrated in studio air too quickly.  Immediate respiratory irritant.  

D-Limonene is another natural solvent like turpentine but distilled from citrus fruit.  Same toxicity as turpentine.  Nice lemony smell is caused by aromatic components which are respiratory irritants.  

Alcohol - A few drops of alcohol helps disperse pigments when making egg tempera paint.  If you want to use alcohol as a component in a painting system, use with the more compatible egg tempera and acrylic paints.  High aromatic component.  Irritant.  Dangerously low flashpoint.

Turpentine - low PEL 100.  Low Flashpoint approx. 100 degrees F. Easily absorbed into healthy, unbroken skin.  High aromatic component.  TOXIC.  

Managing solvents involves fresh air.  Regardless of the media you choose, change the air in your studio before you begin a painting session.  Think hard about your health before you choose to paint in oil colors or acrylic paints if you do not have decent ventilation.  Check with paint manufacturers about solvents contained in acrylic paint formulations before you buy expensive paints thinking they are “safer.”