Hi Phil,

First, these are all solvents, and one can use just about any one of these effectively for the simple task of washing brushes.

However, you should be a bit more discriminating when using a solvent as an ingredient in a painting medium. It is a good idea to avoid the cheaper, bulk quantities of solvents sold in hardware stores, because, while they may be quite suitable for washing brushes, they are usually not pure enough for mixing into oil paint for fine art work.

“Paint Thinner” can literally be anything, but it is usually a form of Mineral Spirits, and usually not very “odorless,” when purchased in a hardware store. Cleaning brushes, yes, but not for including as an ingredient for painting mediums. However, “Mona Lisa Paint Thinner” is a brand of art quality, Odorless Mineral Spirits, and is quite suitable for use with oil paint.

That being said, here is a list of the characteristics of the various solvents, that are suitable for use as ingredients in painting medium.

Turpentine: Strong odor. One of the most compatible solvents for oil paint. Fast drying. Relatively aggressive in its solvent action. It is the distilled sap of a pine tree.

Odorless Mineral Spirits: Low, or no odor. Good, but not quite as compatible with oil paint as Turpentine. Slower drying than Turpentine. Not as aggresive a solvent as Turpentine. It is a distillation of petroleum.

Oil Of Spike Lavender: Strong, but pleasant odor. Very compatible with oil paint. Slower drying than even Odorless Mineral Spirits. More aggressive in its solvent action than either Turpentine or Odorless Mineral Spirits. It comes from a botanical.

I know that you didn’t ask about Oil Of Spike, but it is an excellent solvent, and is one of my main ingredients in my glazing medium. One of its characteristics is a slick, slippery, lubrication capability, when combined with other ingredients in a painting medium.

Of these three, Oil Of Spike is the most expensive, and Odorless Mineral Spirits is usually the least expensive, with Turpentine (good, art store, distilled spirits of Gum Turpentine) somewhere in between these two in price.

That’s about all I can add. I’ve worked with Oil Of Spike as an ingredient in my painting medium now, for several years, and find it quite wonderful with which to work, from its pleasant smell to its application and drying characteristics.

For a solvent to be used with my painting medium, I generally consider its compatibility with oil paint to be my first concern, with application characteristics a very close second. If it works with my paint, toxicity concerns take a back seat. Not much is toxic, provided it is handled appropriately.

I would not recommend the use of any solvent, alone, as an oil painting “medium”. I always include some drying oil (Linseed, Stand, Walnut, etc.) in the mix.

Phil — You didn’t make a mistake, and you can use that OMS for oil painting. I use the Home Depot Paint Thinner for most of my needs, and it is excellent quality. There may be some nasty stuff out there somewhere, but I haven’t come across it!

Here’s a little more clarification:

OMS — the least “smell” of any of these solvents, also the least dissolving strength. “Drying time” is a misnomer — solvents have volatility — they evaporate, not drying like oils. In this regard, these petroleum distillates have a lower volatility and flash point.

Mineral Spirits (MS) — also called paint thinner, is petroleum distillate that hasn’t been “deodorized” to make OMS. It has approximately the same characteristics as OMS, with a little more smell. This solvent is stronger than OMS.

Turpentine — distillate of pine trees and they pitch. More volatile and lower flash point of combustion. Stronger solvent than either of the petroleum products above. Strong “piney” smell, which most people like, but others react to. I only use artist grade premium turpentine — WN is my preference.

Oil of Spike Lavendar — a distillate of lavendar oil. Strongest solvent of these four. The smell is almost universally enjoyed, and used in aroma therapy! Less volatile than Turps, evaporates more slowly. Most expensive, by far.

You can use any of these for making mediums in combinations with oils. The stronger ones are needed when working with resins. Almost any will work to clean brushes, as long as hard resins are not used.

I personally buy the Home Depot MS by the gallon, and putting it in Silicoil jar for brush cleaning, and a small tin Turpenoid can for mediums and cleanup rags. I use turps and spike in mediums, but usually in combinations that include MS, since I don’t really need the extreme dissolving power or expense.

So, you’ve done okay for now, but may want to move up to MS at some point or artist grade turpentine or spike later.

Here’s a little fact that I ran across recently. According to the National Institute of Health Sciences, turpentine is considered completely biodegradable. I have not read anywhere that the mineral spirit derivatives are biodegradable. I guess this makes sense since turpentine comes from trees, while mineral spirits are a petroleum product. Makes me feel a little better about using the turpentine.:)
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I’d have to look up the exact definition of volatile organic compounds and see how it applies to turpentine vapors, so I can’t answer that question directly. I’d guess that since turpentine is an organic substance (it comes from trees) the vapors are VOC’s. But, turpentine does evaporate into the air and the fumes are toxic, especially in high concentrations. Turpentine vapors and skin contact cause all sorts of bad things. Exposure to 75 parts per million (ppm) result in eye and throat irritation, and NIOSH has determined that a concentration of 800 ppm (4460 mg/m3) is immediately dangerous to life and health. So it has it’s dangers, but the small amounts used in painting are not a serious threat if proper precautions are taken – adequate ventilation and so on. There is no practical way for the home artist to determine the concentration in the air you breath, so the more ventilation the better.
Biodegradability and human safety are very different things. Loosely defined, biodegradability is the ability of the environment to deal with the substance, and substances that are biodegradable generally have less of a negative impact on the environment than ones that stick around. Essentially you can safely throw turpentine on the ground and it will be degraded by bacteria and other chemical reactions. Here’s a quote from a government publication: “Turpentine released into the environment is completely degraded by natural processes within a few days. The rate of degradation depends on the concentration of turpentine, temperature, availability of air, and presence of bacteria. Turpentine has been ranked as having zero potential as an ozone depleting substance or for global warming.” See link below for reference.
For those who are interested, there is an 88 page document at the following web address that tells you everything you want to know about turpentine. It’s readable for the most part even if you don’t have a scientific background.
　
Link:
http://ntp.niehs.nih.gov/ntp/htdocs/Chem_Background/ExSumPdf/turpentine.pdf

Petroleum products and mineral spirits are also derived from organic material, trees, plants, microorganisms, they are also biodegradable though the time frame may be longer, thus toxic longer and pose more of an environmental hazard.

Good point, though I don’t think most people think of petroleum products quite that way.

Nothing is less toxic then OMS!
MSDS is just a nervous system irritant and panic generator. I’m not going to work in a gas mask, even if they show a horror movie about the kerosene-killer! I newer go to acrylic and I hate watercolor.:lol:

MSDS data sheets are written so as to cover undercarriages, rear ends that is.
Generators have the documentation in place for when they get sued. Then they can prove that they fully complied and made it known of all the nasties.
As such they unfortunately are a bit over the top. However there is some good data contained within the fluff, such as PEL numbers and chemical identification of constituents.
Soon there will be a new system in place that standardizes them on a worldwide basis, I think they are going to drop the M and then they will be just SDS, safety data sheets.