I posted comments about my painting experiences and how I have not enjoyed using thinner to clean brushes, especially when returning to the task after lunch.
I got a lot of answers as to how to deal with a brush soaked with thinner however I was really looking for the differences in the two chemicals. Thank you for your input. The friend that I work with does have a brush spinner which he raved about several years ago for final cleaning but does not use it during the work day. Actually I think he only uses it when for the final, final cleaning, when he expects to put the brush up of a period of time. Basically our brushes are wet 4-5 hours in the morning and an equal time in the afternoon. The brushes need to be cleaned 2 to 3 times daily any way so the suggestion of covering them for lunch does not solve the cleaning problem that I have. I was aware of that tip however I find cleaning to usually be pretty quick. I prefer to start again or refresh periodically with a fresh brush.
Anyway, through several searches I have deducted that Mineral Spirits and Paint Thinner are not the same in the same sense that Milk and Water are not the same. Yes, paint thinner and milk both have mineral spirits and water respectively but paint thinner and milk are both a bit more complex than what are mostly composed of. What I have deducted is both paint thinner and mineral spirits will both do the same thing however paint thinner as it's name suggests works better as a paint thinner because of the "different" additives that various manufacturers will add. Each has it's own "secret recipe". For the same reason that thinner has mineral spirits and other additives, mineral spirits is a more pure form of solvent.
What I strongly suspect is that mineral spirits actually does evaporate more quickly than thinner, this would explain why I had no dripping going on after cleaning the brushes with mineral spirits vs. paint thinner. It also would stand to reason that paint thinner would have additives that evaporate more slowly so that it would create a mixture that would remain closer to the same viscosity through out the entire can of paint. With mineral spirits used as a thinner I would highly suspect that an open can of paint would probably need to be thinned more than once depending on how long it takes to consume that amount of paint.
I also saw mentioned time and again that mineral spirits used alone is a better degreaser/cleaning agent as it leaves less residue behind than paint thinner. It is a better choice for cleaning petroleum distillates from most mechanical equipment. It has been mentioned that mineral spirits is a better choice than paint thinner to wipe on a surface, such as wood, to show the grain. Paint thinner is going to leave more residue on the surface and will, although very slightly, not show as true, the actual wood color.