What's the difference?

[Devin Lamb]

I make a fair bit of exterior mill work for custom homes, most of which I finish with oil paints (though I know those days are numbered... sigh). Any way, I was cleaning up my mixing bench yesterday, and three jugs of stuff lined up, and got wondering what the difference really was between them. So I've got Varsol, mineral spirits, and paint thinner. Any thoughts on what the actual difference is in them? They all look, smell, and behave the same.

Thanks in advance.

[Jim Rimmer]

I don't know about Varsol but the only difference I know of between paint thinner and mineral spirits is the price.

[Scott Holmes]

That are equivelent in use. Some Paint thinners are not 100% mineral spirits. I think Varsol was a product name used by ESSO (now Exxon)

[Prashun Patel]

Mineral spirits is a distillate of petroleum. It's a hydrocarbon. Naphtha is also a similar distillate, but is lighter in molecular weight. Paint thinner is a catch all that can include these solvents mixed with others. Why mix? The key is that mineral spirits and naphtha are HYDROCARBONS. They are good solvents for things that are also oil based, but for products that contain materials that are not similar chemically, they won't dissolve that well. So, paint thinner might dissolve a wider array of things than the other two. It's cheaper generally because there's no standard formula, so mfg's have lattitude about how to make it.

Varsol, Isopar, and other names are usually proprietary names from companies like Shell or Exxon to indicate precise fractions of the distillate; it just means a tighter bound on the molecular weight of the chemical in the jar, and hence a 'purer' product. In the case of Isopar, there are a bunch of letter grades depending on the weight you want. For us ww'ers, this means you pay a little more for something that provides no practical value. But for cosmetic or other companies, this purity may be useful for them.

Mineral OIL is just a heavy distillate of the very same material as Mineral Spirits. It's so heavy, though, it doesn't evaporate, which is why they use it as a 'finish' on things like cutting boards.

[Harvey Pascoe]

Thanks for that, Prashun. Useful information. Do you know if any thinner makes any difference as between poly and standard varnishes, as for example the final gloss?

[Scott Holmes]

Harvey,

The only varnishes I've used that seem to work better with the manufactures thinner are Behlen's Rock Hard TableTop varnish. Don't know why, I just don't like the way it thins with regular MS. Sherwin Williams Classic Fast Dry Oil Varnish is another that I don't thin with MS I use naptha instead.

[Devin Lamb]

Thanks a bunch guys! Always wondered what the difference was. Always good to understand the nature of the products you're using rather than blindly trusting in what is common practice.