[QUOTE=Allan Rahbek]I . . . treated in a way that removed the harmful parts. . . I can smell that it is petroleum . . .
No doubt some components are removed from the mineral spirits along with the "odor". Don't rely on that. Any aromatic hydrocarbon that evaporates into the air is harmful if the concentration is high enough.
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Originally Posted by Allan Rahbek
How do you ( and others) use it for painting? . . .
I usually use a mixture of 1 part stand oil, 1 part linseed oil with drier added, 3 parts vegetable turpentine.
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Allan, it's just a solvent. As such, it is more or less useful to reduce the viscosity of heavier vehicles, such as stand oil. I believe you mentioned you would use it for cleaning brushes? Good idea. There is no good reason to replace pure spirits of gum turpentine with this stuff in your painting practice. Turps is better for your paint films.
The subject of mediums is a minefield. I question why you mix linseed oil (with a drier) and stand oil with a solvent (turps) ?? What do you feel this accomplishes?
In the main, a useful "medium" centers around a natural resin chosen for the spcific properties it imparts to the quality of a paint film, either for its visual character or handling. Mastic, Copal, Damar, all are capable of imparting notably different qualities when added to paint. Canada Balslam, Strasbourg Turpentine, Venice Turpentine impart yet another, but are so similar to one another as to yield near identical results, although each most certainly has identifiable individual characteristics.
A medium that includes resins needs to be balanced with enough linseed oil to remain flexible. Whether the oil is heat-treated (as stand oil is) is yet another variable.
Finally, the combination of oil and resin usually requires the addition of a solvent to control viscosity and possibly drying time.
Allan, if you are employing a mix of oils, turps and a siccative, the addition of the siccative would be the cause of your paint drying on the palette sooner than you may like to see.
Perhaps your new-found solvent is less volatile than turpentine. If so, yes, it would slightly retard the drying time of a given paint (minus the siccative in the mix). To answer this question, one need only place small equal amounts of each in open containers, and note any difference in the rate of evaporation. A clean glass palette is ideal for this test, and would have the added advantage of allowing you to ascertain whether the petroleum product leaves any residues.