I was recently discussing ways to mitigate surface irregularities during the painting process, as opposed to varnishing, with a specialty paint merchant. They recommended reducing the amount solvent in my medium and using a less bodied oil like walnut for flow, which seems like good advice. However, they also recommended switching from Gamsol to double rectified Pine Turpentine, which I have questions about.
I currently use a 50/50 mix of Gamol and Linseed oil and my paintings aren’t too many layers.
I know Turpentine and Gamsol have a different feel under the brush, but would turpentine actually help to create a more mat, uniform surface?
The merchant disagreed with me about Gamol being a less toxic solvent, which I’ve always been told. If I’m understanding the MITRA Resources pdf on solvents (word in parenthesis my own)- “Aromatic hydrocarbons (like turpentine) tend to evaporate more slowly and are more toxic than aliphatic hydrocarbons (like Gamsol)”. Can you confirm that Gamsol is indeed safer?
Thanks in advance for any thoughts!
Thank you so much, Brian and Matthew!
It sounds like the consensus is that Turpentine is more matte and more toxic, and Gamsol is less matt and less toxic. I might be getting hung up on a technicality, but just to make sure I understand —
The resources pdf notes that “Aromatic hydrocarbons tend to evaporate more slowly and are more toxic than aliphatic hydrocarbons”, but Brian mentioned, “It is true that faster evaporating solvents tend to create surfaces that are more matte.” If Turpentine is Aromatic (slow drying) and Gamsol is aliphatic (more quickly drying), wouldn’t this mean that Gamsol dries more matte?
Thanks again!
Yes I am hoping to understand which solvent mixed with paint will be the least shiny. It sounds like terpentine is the answer. I’ll stick with gamsol for safely though. Thanks for all the detailed information, Matthew and Brian! Its difficult with a non-science backgound to fully understand, but I’ll keep experimenting and keep going back to these threads for reference as I do.
Odorless mineral spirits (no aromatic component) like Gamsol are safer in terms of health. This is not debatable. It is true that faster evaporating solvents tend to create surfaces that are more matte.
Oil paint diluted with pure gum spirits of turpentine does dry with a more matte appearance, but I would not agree that it is necessarily more uniform, because the matting effect is not always consistent between passages. In my experience, paint that retains some degree of gloss when it is touch-dry will have a color that is closer to the range of wet paints on the palette; this, in turn, makes it easier to coordinate the next application of paint.
Evaporation is more complicated than that. It is related to molecular chain length and functional groups. For instance, toluene evaporated more quickly than xylene even though they are both 100% aromatic. Turpentine has some aromatic components but it is a mistake to assume that it is the presence of aromaticity that confers the slower drying rate. Short chain aliphatic solvents dry faster than longer chain aliphatic solvents. The solvent(s) that make up Gamsol appear to have been chosen specifically due to their even and longer drying rate. This certainly makes sense if one is trying to provide the least toxic solvent as slow drying limits exposure.
When you write “Gamsol is more Matte” I assume that you are referring to paint and/or varnish diluted in the solvent as the solvent itself does not confer and sheen.
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