With learning about how paintings were made in 
  centuries past, much attention is always paid to 
  the how the studio is run, with apprentices doing 
  the work of grinding oil into pigment, and to how 
  difficult obtaining colors could be. I am very 
  interested in pigments, but that story seems to 
  be missing the other half of the paint. 
    Oil.
    In contemporary painting, oil paint is mostly 
  made with linseed oil.  But what is linseed oil?  
  It comes from flax right?  What was done to flax 
  seed in order to make linseed?  The more I looked 
  into this, the more elusive the answers seemed to 
  be.   Most literature I can find avoids the topic 
  altogether, and older books still in print, have 
  just brief descriptions of boiling it.
    My wife then surprises me by giving me a present 
  of a hand powered oil expeller.  And so I began 
  experimenting with extracting oil.  But the oil 
  has to be 'refined', but how would that be done 
  without boiling?  After some communications with a 
  few paint manufacturers, I felt a little more
  confident I was on the right track, and then 
  discovered online someone else refining his own 
  oils, with recipes on his website. 
    Turns out the process is pretty simple but 
  strenuous. Following these steps I have been 
  making all the oil I use in the studio both to 
  make my tubed paints, and as a medium to use 
  while painting for the last several years, I feel 
  that this process, along with other historical 
  practices, have helped me bring my art to a 
  higher, more personal level.
    I am not an expert of much of the science behind 
  how and why, but I am passionate about learning 
  techniques and materials of a time when painters 
  were not called artists but craftsmen. 
  
Tad Spurgeons book is a great resource for info 
about the refining process of oil's, and a great 
book all around. Highly recommended!
Joseph Besch
4/10/16