Here's an interesting catalog description of an exhibition that just closed, Frank Auerbach: London Building Sites 1952–62 (http://www.courtauld.ac.uk/gallery/exhibitions/2009/auerbach/index2.shtml)
He did plenty of interesting, strenuously-crafted work, but one line that caught my attention was:
Posted 7 months ago #As he worked and reworked the composition, his paint surface became ever thicker as he strove to express what he describes as “the core” of his subject. The result is a painting more than an inch thick in places in which the sheer weight and density of paint threatens to collapse in on itself, obscuring the image completely.