Turpentine vs Naphtha for Oil Painting
Saturday August 5, 2023
In my post about Mark Boedges workshop I mentioned that Mark specifically uses turpentine instead of OMS for his first layer because of its drying time. Turpentine drys about 3 times faster than OMS. Another petroleum distillate, VM+P Naphtha actually dries faster than both. I couldn’t find a whole lot of information on using naphtha for oil painting so hopefully this will be useful to someone. I’ll dedicate this article to my solvent experience/experiments and update it as I collect more data.
I should note here that I only paint on oil primed surfaces. I’ve used both Raymar double primed linen panels as well as diy panels primed with Zinsser Cover-Seal. Aside from the texture, there’s not much difference in the way that paint sits on them. I would assume that most of the principles are the same when painting non-oil primed surfaces but you should expect your color to sink in more.
Also as a note, soft brushes are required for layering over wet paint. Rosemary Co. Master’s series are great. I’ve been doing 80% of my painting with them. The first 19% is with the Ultimate Bristle and the last 1% is Eclipse Long Combers. If I were to suggest a bare minimum brush set I would pick one or two large Ultimate Bristles and maybe three or four Master’s Series. All long flats plus a rigger. The Eclipse I don’t really use unless I feel like my brush strokes are getting boring and just want to change things up.
Paint Thinner, Mineral Spirits, OMS, “Turpatine”, “Turpenoid”, “Gamsol”
All of the above are names for essentially the same thing. Petroleum Distillates. Regular old paint thinner or mineral spirits is unfiltered petroleum distillate. It cuts well but contains lots of nasty stuff that stinks and gives you a headache.
Odorless mineral spirits is the same thing but they filter out the stinky parts. Unfortunately the reason the stinky parts stink is because they evaporate quickly. That means the less stink you have the slower it dries.
Turpatine, Turpenoid, and Gamsol are all names for some companies concoction of “mineral spirits”. I’m sure there’s some minute differnece between them but as far as I’m concerned they’re the same. All of these solvents are petroleum distillates with a slow evaporation rate. No petroleum distillate solvent will cut natural resins like damar. Keep that in mind when mixing mediums.
Turpentine is the classic oil painter’s solvent. It smells like pine trees and it’s real bad to breathe in. Really, every solvent you use painting is bad to breathe, but turp at least has the decency to give you a heads up. As a solvent to actually paint with (not just clean brushes) turpentine is highly superior to OMS. It dries about 3 times faster and cuts much better. Turpentine is also the only solvent that will disolve natural resins like damar varnish.
Varnish Maker and Painter’s Naphtha
VM+P Naphtha is another petroleum distillate like OMS. It’s sometimes referred to as “White Gas” and is apparently the same thing as lighter fluid (it burns in a zippo at least). It dries faster than turp and it cuts even better. It insta cures crusty brushes and palette build up and the smell isn’t oppressively strong like turp can be. Sounds great right? Well there’s a reason people still use turp.
Remember how OMS is made by taking the stinky part out of regular mineral spirits? Well this is the stinky part, or at least one of the stinky parts. The reason it dries so fast is that its highly volatile, meaning it gets in the air faster than turp or OMS. While it’s not significantly more toxic than turp, due to the high volatility, I think it reaches toxic levels in the air faster than turp does (based on personal experience, I hope not to collect much more data on this point myself). The smell is less intense than turp but its not at all pleasant and subtlety is not really a positive attribute of carcinogens. Like OMS, it will not thin damar varnish.
Which one should I use???
It depends on what you want your solvent to do.
For thinning medium without natural resins I think OMS is still the best choice. In this case the drying time is going to be most effected by the medium itself rather than the solvent so using turp or naphtha isn’t really worth the fumes. If you wan’t a fast drying medium then Galkyd or Liquin will do the trick. Turp or naphtha might further decrease drying time but I expect my paint thinned with medium to remain wet while I paint so I’m not really concerned with that. The obvious exception would be if your medium has damar varnish or any other natural resin that is only soluble in turpentine.
For cleaning brushes OMS is the clear winner. I might use naphtha if I had a really dirty brush but for mid-paint rinsing there’s no advantage to using anything other than OMS.
As a thinner for washes turpentine and naphtha are pretty equal, each with their own pros and cons. Naphtha dries extrememly fast which is great for painting with a time limit (the only kind of painting I can fit into my life). Because it drys so quickly I feel like I’m able to get darker washes which helps me start seeing the finished picture faster. Turp, because it stays wet longer, runs more which can create some interesting effects. It’s also marginally less toxic and I think the odor is more pleasant even if it is stronger. Naphtha, while mild, has very industrial odor that is not at all pleasant. The mildness seems like a pro but in reality naphtha is more toxic than turp. Not smelling it just means it’s possible for me to forget about it and wind up with a splitting headache because I forgot to cap my jar. Turpentine has a distinct piney smell to remind you to cap it before you get cancer. For the way I currently paint, naphtha is my preference, even if it means I have to be more vigilant of poisoning. I could see myself switching to turp if I were working on larger paintings with less of a time crunch.