Thread: Mineral Spirits
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Old 05-19-2006, 08:42 PM   #8
Richard Bingham Richard Bingham is offline
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Joined: Jan 2006
Location: Blackfoot Id
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A few other points of interest:

Turpentine, strictly speaking is the gum exudations of pine trees. Pure spirits of gum turpentine is the distillate. Rosin is the solid resin which that distillation leaves behind.

Currently, most "hardware store" turpentine is derived from the steam extraction of forest waste products (stumps and limbs) and smells nastily of creosote. This is to be avoided for purposes of oil painting. Good turpentine smells like a fresh pine forest, and in fact most of the "good stuff" goes into the making of all those pine-scented air-fresheners and other similar household products.

Cutting natural resins such as mastic or dammar with petroleum distillates results in a cloudy varnish.

Used as a solvent to control the viscosity of paint or mediums, turpentine has chemical advantages over mineral spirits; combined with linseed oil, turpentine forms hydroxides by absorbing free acids in the linseed oil. Hydroxides draw atmospheric oxygen, causing paint to dry throughout the film rather than only from the "top down" , which one notes when fresh paint "skins over".

In my opinion, mineral spirits is a convenient solvent for cleaning brushes and tools, but is best omitted from paints and mediums. Odorless or not, MS releases volatile hydrocarbons as it evaporates, same as turpentine. Adequate ventilation in the studio and sensible, sparing use of all solvents are necessary for safety. Turpentine is neither more volatile than MS, nor particularly flammable; a lighted match can be extinguished in it.
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