I use a medium for dipping into my colors on the pallet part of an “ingredient” used by Thomas Cole, among others.  I use Unrefined Walnut Oil.  And three others.
  
This facilitates the time I have to wait between layers.
  
I make my own colors from dry pigments; also some tube colors. In either case my medium works to great advantage in producing paintings like this one in one month to six weeks that would in my old days would take up to six months or longer.
  
This does allow for varnishing much sooner than if I were using my old medium that includes Damar Varnish.
  
What does this mean?
  
It means that within a week I can varnish the painting, as opposed to having to wait six weeks for the work to dry.  And that what you see here has “sunken” areas because different colors dry at different rates.

And that means that the painting will, in a week be totally integrated as to colors.