Part 2
Summary: Understanding something about solvents arms us with the knowledge that can help us make artwork as safely as possible. Unfortunately, solvents are extremely complex, and the chemistry is difficult to decipher. Product literature does not provide as much assistance as we might need with helping us understand the solvents to use.
Another source of confusion in a magazine article I read states that mineral spirits is a modern, 20th-century product. This is only partially correct. The highly quoted author on art materials, Charles Eastlake, uses the term “naphtha” ten times in his book “History of Oil Painting” published in 1847. Eastlake defines naphtha as a petroleum-based solvent. (Petroleum - the root source of mineral spirits) An even more frequently cited modern resource of information on past painting and conservation practices, “Painting Materials” by Rutherford Gettens and George Stout published in 1942 defines and discusses “naphtha” eleven times and traces its use back to antiquity.
Here is the crux of what is misleading about labeling mineral spirits a modern solvent. I can’t help but to bore you with the details. But hang in there. Some of them are important to you as artists. The naphtha cited by Eastlake relates to its use during a variety of periods long ago. Gettens and Stout write about naphtha’s origin in antiquity as a petroleum derivative and more recently as a solvent extracted from coal tar. (It is the same coal tar that is the source of colors first discovered by William Henry Perkins, see https://www.syntaxofcolor.com/post/divine-aniline-won-t-you-be-mine
In the end, everybody is describing the same petroleum-based hydrocarbon derivative, but in different periods and with different hydrocarbon combinations. A solvent’s name evolves as more and more sophisticated distillation processes provide the ability to segregate different segments of hydrocarbons. The naphtha used by artists in antiquity is a far cry from the mineral solvents available today. Understand that crude petroleum can be cracked and divided into products such as gasses, raw materials for plastics, gasoline, aviation fuel, kerosene, and solvents by isolating very specific segments of hydrocarbons. The many products extracted from oil create materials with characteristics that are classified by their boiling points, gravity, evaporation rate, combinations of petroleum components, etc.
The paint industry has created terms that clarify what is contained in these segments of petroleum derivatives. If Eastlake could have understood and defined what is in the naphtha he was describing it would be very different from what you as a consumer can purchase in a hardware store that is currently labeled VM&P Naphtha. Describing Stoddard Solvent as a material fabricated for use in the dry-cleaning industry is correct, but its origin is not a newly discovered material. Stoddard Solvent was just another distillation product created for a specific use, in this case, dry cleaning, Stoddard Solvent needed to be highly volatile so that it cleaned effectively and evaporated quickly so as not to linger in the item being cleaned. Nobody wants to pick up their dry cleaning and have it smelling like solvent.
The solvent that encompasses what is called “mineral spirits” is divided into distinct materials with different working properties. Common hardware store mineral spirits are classified as: “Regular.” That contain 15 to 25 percent aromatic hydrocarbons; “Low Odor” mineral spirits that have varying amounts of a range of hydrocarbon combinations that are not openly defined in the product literature, and “Odorless” spirits that have open chain aliphatic hydrocarbons. (Fine Woodworking website)
Confused yet? You should be. Solvent chemistry is not meant to be understood by mere mortals. Petroleum is so complex that when it is subjected to distillation (like the process of extracting alcohol from fermented grains to create vodka or whiskey, etc.) the number of distinct chemicals that petroleum can be separated into is mind-numbing. We hear terms such as naphtha, benzene, xylene, toluene, and heptane and know they are petrochemicals, but it takes deeper knowledge of chemistry to understand what part of petroleum they are derived from, what a particular solvent is good at doing and more importantly for end users, how dangerous is the hydrocarbon distillation we might select to use.
As hydrocarbons are more refined (segregating various hydrocarbon groups) they have different characteristics, and these are technically important for commercial manufacturing where boiling point and the working properties of solvents have an impact on the purpose of their use.
Artists have a practical history related to understanding and using mineral spirits. Less refinement provides the classic very smelly odor (Regular solvent) that many artists have either grown to love or hate. Removing the smelly aromatic hydrocarbons creates a more highly refined version that is labeled and sold as “Odorless” mineral spirits. The refinement can go even several steps further when specialty mineral spirits are created that are both odorless and very slow to evaporate. A cursory look at the long list of hydrocarbon solvents sold by Shell Chemicals provides a seemingly endless group of solvents with a range of boiling points, evaporation, density, and types of hydrocarbon molecules in each product.
Thinking that all mineral spirits are the same can be both confusing and dangerous. Every solvent has defined exposure and toxicity levels, even those that do not have an odor. Everyone should treat solvents with respect and safeguard against unnecessary exposure. Awareness along with reported sensitivity to solvent fumes has motivated many artists to redesign their painting methods to use no solvents or only employ them during cleanup.
We should know from a variety of sources that we should not use any solvent that contains benzene, a well-documented carcinogen. It is the main reason that, in my opinion, I would never use or recommend that anyone use inexpensive commercial hardware store solvents meant for use by the building and painting trades. Remember that in the manufacturing world, a company that employs solvent working in compliance with health and safety regulations, knows what harmful materials are in a solvent and they have measures to curb worker exposure to dangerous hydrocarbons. Artists generally don’t have the luxury of a health and safety expert to guide them, so selecting a solvent that has well-documented literature, especially marketed by reputable companies catering to artists, helps to assure that they researched to select solvents that do not contain the worst, most toxic substances.
So, be careful what you read about solvents. When you purchase a new product, especially a solvent, research what it contains from several sources and figure out if it is suitable for you to use. Years ago I met several artists that followed exactly what their instructors told them. They swore that using kerosene was a wonderful painting diluent. A few artists swore by Stoddard Solvent or VM&P Naphtha. Decades ago, nobody discussed what potential carcinogens were in some of these commercial products. In graduate school, I heard sad tales of printmakers active in the 1960s and early 1970s who came down with horrible cancers. Their students witnessed them “bathing” in solvents up to their elbows when cleaning silk screens and printing equipment. Personally, a distant cousin was employed by a newspaper to clean colored oil-based inks from printing presses each night using powerful solvents. His life was cut short by many years.
Let’s be safe and knowledgeable about the products we use so that we all can enjoy a long life of producing wonderful works of art.
AMENDMENT: I believe I was not clear enough regarding what to look for in selecting a solvent. The vexing problem is that solvent manufacturers, especially those who make products sold in hardware stores don't provide detailed information about all the components in the solvent they sell. Most data safety sheets indicate the words, "Petroleum Hydrocarbon" which is not very helpful. While Section 2 of the safety data sheet gives a bit more information such as "Stoddard Solvent" and a CAS (Chemical Abstract Service) number, the next question you would ask is, "What is contained in Stoddard Solvent?" The breakdown of the details of all the hydrocarbon groups that are in the product you select to potentially purchase is rarely presented in detail. Missing is any information about solvent groups within the product that might have more or less harmful components.
However, pay attention to the part of Section 2 of the safety data sheet for a product that indicates the PPM, (parts per million) of exposure time that is published. If it is printed in this section, a lower number indicates a more toxic solvent. A solvent with 100 PPM is more harmful than a solvent with 300 or 400 PPM. Do the same research on products that say "Natural." Some of them may have volatile organic compounds (VOC) that require the same safeguards you would employ using hydrocarbon solvents. In most cases, you get what you pay for with solvents.
Those high-priced solvents sold to artists have been selected by art materials manufacturers because they are highly refined, meaning the distillation product in the solvent has a very specific hydrocarbon group. Solvents like these have been marketed to industries because they have performance characteristics matched to a task a manufacturer needs to maintain. Artists benefit from the purity of the solvent that does not contain hydrocarbon mixtures found in inexpensive solvents.
Syntax of Color