Wednesday, November 10, 2010

Ask Stape, about solvents, safety and longevity

Dearest Stape:

You may have answered this question ad-nauseam by now, but I've been doing some research and need to know - because I love to paint wet, juicy oil paintings, about 3 different mediums solvents.

Natural turpentine seems to be the best - but there are differing "opinions" about how toxic it really is for studio use. Then - Gamblin Gamsol - a petroleum product doesn't seem that archival - is it?? Gets good reviews in the safety category. Then - last, most importantly, and my most favorite is Orange Turpine - Eco House - 915. I Love the stuff, but again - what's the truth about the toxicity and particularly the archival qualities of it???
Astrozenica Rhodococcus

Dearest Astro:

I referred your question to my friend and chemistry wiz Robert Carter, a painter and reader of this blog. The following is his answer. Robert has the ability to make the complex understandable to laymen like me.


To answer this definitively, I pulled up the Manufacturer’s Data Sheets (MSDS) for turpentine (Utrecht), Gamsol (an odorless mineral spirit, OMS) and Eco-House Natural Orange Turpene #915. I have no experience with the Orange Turpene product, but it’s interesting to see that it is being promoted as a safer solvent that will dissolve damar. The principal ingredient is food grade orange turpene oil, which has an FDA GRAS rating (generally regarded as safe). GRAS is applied to most foodstuffs on the basis of long experience (e.g., spices are on the GRAS list), but there is no presumption of rigorous testing.

The health concerns of any solvent are acute toxicity on the one hand, and long-term health risks on the other. On both counts, turpentine is definitely the worst, Gamsol (and other OMS products) are better, and Orange Turpene is the (presumably) most benign. As the Merk Index notes, turpentine is absorbed through the skin, lungs, and intestine. It causes acute skin and mucous membrane irritations, skin eruptions, gastrointestinal irritation, delirium, ataxia (loss of muscle coordination), kidney damage, and coma. Inhalation causes palpitation, dizziness, nervous disturbances, chest pain, bronchitis, and nephritis (kidney irritation). Chronic contact can cause benign skin tumors. All in all, we’re better off not using it, except when necessary (e.g., damar-based mediums). OMS has similar risks, but they are generally regarded as less acute. In part, this is because it is less volatile (has a lower vapor pressure) than turpentine, so the build-up of vapor in the studio over time is lower. Certainly the narcotic effect is less. But among OMS products, there is a great deal of variation in the composition of the hydrocarbons present. Gamsol’s claim to superiority is that it is very low in aromatic hydrocarbons (less than 0.02%), which potentially reduces the long-term safety concerns. Chemists these days are very concerned about the use of volatile organic compounds (VOCs) in synthesis and manufacturing, but most especially about aromatic hydrocarbons. Aromatic hydrocarbons are composed of planar, six-member rings of carbon atoms, with benzene (C6H6) being the parent compound. Years ago, we thought nothing of doing reactions in benzene, but today you have to jump through hoops just to buy a bottle. The problem is that benzene is carcinogenic. So anything that minimizes benzene and other aromatic compound content is preferred. The Orange Turpene product, having ingredients on the GRAS list, is presumed to be safe. But we should throw in a word of caution here – GRAS just means we don’t know of any problems. Just because something is natural does not mean it is necessarily benign. In the absence of data, one should still take reasonable handling precautions. Beyond this, the only other thing I spot in the MSDSs is a difference in the flash point temperatures: 91o F for turpentine, 113o F for Orange Turpene, and 145o F for Gamsol. This is the same order as the boiling points. It means that the potential of starting a fire in the solvent is least with Gamsol. But this is really a minor concern.


The principle to apply in evaluating for longevity is that simple is better than complex. The process of forming a paint film (“drying”) is actually an oxidative polymerization process. Polymerization is the joining together of smaller molecular units (monomers) to make an infinitely large structure. The strongest polymer, and hence the strongest film, would be formed from a single vehicle (e.g., linseed oil), because only the same kinds of monomers would be joined. With a variety of alternative monomers present, the network building frequently ends in dead ends or less strong linkages. Now that’s the theory, but in practice it may not make a big difference. For example, white paints frequently have a mixture of linseed oil and safflower oil to reduce the yellowing tendency, but I do not know of any data that says these make weaker films than a white mixed with, say, pure linseed oil. So, how does this apply to solvents? Well, we need to think about the residue they leave. Looking again at the MSDS data, Gamsol is 100% volatile, turpentine is 99.5% volatile, and Orange Turpene is 99% volatile. The latter two, then, leave a nonvolatile residue in the paint. We have hundreds of years experience with turpentine, so we know that the oily residue it leaves does not interfere with the polymerization of linseed oil, and may actually be incorporated into the film. At least in theory, Gamsol should be even better, because it leaves no residue to interrupt polymer formation. In other words, your questioner is misinformed to think OMS compromises longevity. The Orange Turpene leaves 1% residue, so the question is what effect if any does it have on the strength of the film? The manufacturer claims that this material is archival, but it is a new product that does not have the lengthy record of turpentine, or even OMS. They may be right, but they could be wrong. As far as I know, orange oil (which is 90% d-limonene) is not a drying oil, which means it does not readily polymerize on exposure to oxygen. If that is the residue, it could be a problem. But to be fair to the product, I am speculating here.

Speaking personally, I tend to be very conservative about materials with respect to longevity. (By contrast, painters like Fairfield Porter loved to mess around with odd materials, and now their paintings are employing legions of restorers trying to hold them together.) I avoid turpentine, except when necessary, only because of the health issues, but certainly not because of longevity concerns. I prefer OMS because of health concerns, and I am confident it poses no compromise to longevity. (As an aside, if someone with the technical expertise of Robert Gamblin doesn’t have a problem with it, then I don’t.) Personally, I would be reluctant to take a chance on this new orange product. I know, for example, that Turpenoid Natural should not be used as a painting medium solvent, so I guess that prejudices me on this stuff. Maybe I’m just reacting to the knowledge that if I really wanted to mess up my paint film, I’d add orange oil. That’s like adding Goo Gone. I guess if you like the product and you’re willing to take the manufacturer’s word on its archival nature, then go for it.

Hope this helps.

Robert L. Carter, Chair

Department of Chemistry

University of Massachusetts Boston

Thank you Robert, That was great!.....................Stape


Unknown said...

Robert, you ARE smarter than a fifth grader!!!
I just ordered a gallon of Gamsol, so I'm hoping Robert is correct!
I tried the orange stuff and all I can say is that it is oily and weird (does smell nice though). it did not react well when I applied some Liquin to a painting in progress so I could work into wet... so, I'll stick with the Gamsol for the studio. Outside, I don't think it matters so much.. you are not breathing the fumes in any concentrated form.

Marc Dalessio said...

I was hoping by longevity you were going to tell us how to live longer.

Great post anyways.

jeff said...

For mediums I only use turpentine.
I have always been suspicious of using OMS for a painting medium.

I use it to clean my brushes.

I work clean and with very little medium.

One could make a medium using Spike Oil (Lavender oil, not the kind you get in a health food store). I use this as mix sometimes in my mediums.

Stand oil, Canada Balsam, and Spike or Turpentine.

Spike and CB smell great, but I still use a small cup and when I'm done I cover it up. Spike Oil is not safer than turps as far as I know, it only smells better.

I have friend who uses turps in a large can, about the size of a tuna-fish can, and his studio stinks. I draw there sometimes when he is painting and I have to say it's a little irritating if he forgets to turn on the vent fan.

Thanks for the post, it was very informative. said...

In short, I was told by a conservator at the Metropolitan Museum of Art that conservators hate all mediums. And now, after reading the explanation here, I understand why.

For people who are greatly concerned with health implications, you can use safflower oil to clean your brushes (or pallet knife). It's a drying oil and you can get it at the supermarket.

My husband, about 30 years ago, pass out after cleaning himself up with turpentine. Have no doubt that it passes through the skin into the blood stream very quickly. He fell to the floor with the room spinning and woke up hours later with a horrible "hang over". And last year, a painter friend of mine got sick holding on to his turpentine soaked rag while painting. Terrible headache etc.... Now he wears a glove on that hand.
I am sorry, I really don't get the artists sticking to their turpentine as a solvent .... And they can't explain it except to say that's what the old masters used.

Cynthia Hillis McBride said...

Thanks for passing on this info. It was great. I am curious now about various mediums, their properties, longevity, drying times etc. I have been experimenting lately with cold wax, but am suspicious of it's archival strength. Have you previously written about mediums and I have just missed it?

Steve Baker said...

I feel like I should add my personal experience to this. I am an amateur painter not a doctor or a chemist. Several years ago I was lying in the bilges painting under the deck in my boat. It was a hot August day. Evidently I had spilled some mineral spirits and got it on my back. After cleaning up and going home I found that a large patch of my back was swelling and turning bright red. I went to the hospital and was sent away thinking it was just a burn. The allergic reaction (had used the stuff for years with no problem) that followed was amazing. My entire body became swollen. I had no "figure" prints on my hands or my feet. I could not hold a fork for the pain. My skin hurt. This lasted 3-4 days and them when the swelling subsided sheets of skin peeled off and my whole bodied shed like a snake. Since that I have also been hospitalized when an accelerated heart rate, according to doctors the result of exposure to fumes. I now keep benidryl on hand and if I feel that familiar tingling sensation I take it immediately. Just because it is "safer" does not mean it is safe to slosh around like water. I use turpentine with restraint and ventilation.

Mary Byrom said...

Great post - Thank you Robert. I often don't use any medium. I started painting with just plain paint. I liked the way I could control it. In school the instructors used only linseed oil as a medium - but I just thought it made everything very slippery so I ignored that part of their instruction. Then while painting en plein air I bumped into people dipping their brushed into a little container of "something". So I started asking around and everyone had all kinds of potent mixtures they swore by. I think the "medium of choice thing" goes back to the paint and the substrate you are painting on (depending on the effect you are after). Some surfaces need one, others don't. Gamsol & stand oil are is great when its -20 and the paint is stiffer than cardboard and doesn't want to leave the brush. Mineral spirits clean my brushes.

Anonymous said...

Has anyone worked with the M. Graham walnut oil based pigments. I've given them a try lately and the jury is still out?

And on a different note...thank you to Stape for the in-depth on Sargent, particularly the dissection of the edges.

Time to go wander in the desert mountains. Life is good.

Philip Koch said...

That post included a good short and sweet description of polymerization. Now I'm ready to explain something I've never been clear about (well, explain it at least a little).

Rae O'Shea said...

Where does turpenoid fit in this?

JonInFrance said...

This blog is such a pleasure to read - a high spot in every day

Florante Paghari-on said...

I do really like your explanation about those solvents and especially their effects to our health ,Stape. I use turpentine before to make a painting medium, mixing it with damar gloss varnish and stand oil but i always got headache when using it and trouble with breathing.Stape,do you think stand oil with Gamsol (OMS) is good enough as an all around oil painting medium?

billspaintingmn said...

I have decided to wear a glove when painting, I don't need any surprizes on this side of the canvas. I still experiment with mediums, I wash brushes with mineral spirits.
(I've heard walnut oil in place of linseed oil~)

Terry Krysak said...

I did a search on the CAS # (Chemical Abstract Number)for the product as listed in the MSDS

and the most notable issue was that under normal conditions the product ingredient will decompose rapidly & acquires a terebinthine odour.

Any time that you are concerned about volatile solvents you should use a half mask respirator, or North provides the N95 mask that does provide protection against vapors from volatile organic compounds.

In my life before retirement, I established the WHMIS program for The City Of North Vancouver, and also was a certified TDG instructor.

J Hopper said...

That was indeed Great! Thanks so much Stape and Robert - for taking the time to write all that out for us. It is incredibly helpful info - stuff I've been mulling over for some time - I will be going with the Gamsol as well - Gamsol and stand oil. Don't care for the shine with the damar added. So happy to finally have some definitive answers!

Judy P. said...

Interesting post! I try to use no medium while painting, and I clean my brushes with Turpenoid Natural, which is nicely orangey-smelling and non-toxic (at least that's what the green container says). It's also a stronger cleaner than OMS, to my mind. I'm also going to try Fels-Naptha soap for brush-cleaning- I read it's cheap and effective.

Stapleton Kearns said...

Robert is wicked smart and owns the best cowboy hat imaginable.


Stapleton Kearns said...

I can only tell you how to live to 58. After that you need a a better mentor.

Stapleton Kearns said...

I think that spike lavender is too expensive for my use.

Stapleton Kearns said...

I spent half my life soaked in turps and never had a problem. It must vary a lot by who you are. I of course, have no internal organs as you know.

Stapleton Kearns said...

I have written a little, search the archives using the box at the upper left.

Stapleton Kearns said...

I almost never use turps anymore. The good stuff is to expensive.

Stapleton Kearns said...

Straight paint is the best possible way to go I think.

Stapleton Kearns said...

I have used their alkyd Walnut oil medium. It has a nice gloss and a scary flammability label on the can.

Stapleton Kearns said...

I have used their alkyd Walnut oil medium. It has a nice gloss and a scary flammability label on the can.

Stapleton Kearns said...

That was a good clear explanation.

Stapleton Kearns said...

I don't know. I will find out. But not tonight.

Stapleton Kearns said...


Stapleton Kearns said...

Yes I think that will work just fine.

Stapleton Kearns said...

I still think linseed oil is the nuts.

Stapleton Kearns said...

I wish you Canadians spoke English! I don't understand what you are saying. Please clarify for the uninitiated.

Stapleton Kearns said...

Well done, J Hopper!

Stapleton Kearns said...

I was recently given a can of that. I will you know what I think of it. It sure tastes like shit.

jeff said...

Stape I only use it in mediums.
I would never clean my brushes with it. It is expensive.