Pressure flaking, apparently in evidence in the Still Bay occupations at Blombos Cave, is a level of sophistication in stone tool making, thought previously to have been initiated during the Upper Paleolithic in Europe. Pressure flaking as a technique is an advance on stone tool technology, because it allows a finer, more precise cutting edge to be created. The control exhibited in pressure flaking is the first step towards the ability to make tools for specialized tasks: for cutting meat off bone, for scraping hides, for making drills, for the myriad of things that stone tools can be used for. A little bit of history about stone tool making is clearly in order.
Creating the ubiquitous Lower Paleolithic stone tool called an Acheulean handaxe (first made some 1.7 million years ago) involves removing pieces of stone from an undressed flint or chert block using a hammerstone. A hammerstone is usually made of groundstone, something that won't easily shatter and send chert flakes flying. The Lower Paleolithic flintknapper created a bi-convex lens-shape form by a series of, well, banging two rocks together.
Pressure flaking involves a level of sophistication not seen in the Lower Paleolithic. After the roughly lens-shaped form has been created, the knapper takes a bone or antler baton and presses it against the edges of the stone blade, removing smaller flakes and producing a sharper and more defined working edge. On some cherts, such as the local silcrete used by Middle Stone Age flint knappers at Blombos, successful pressure flaking requires heat-treating.
Heat-treating is exposing raw stone to the heat of a fire for a few minutes, which recrystallizes the stone and makes the stone more amenable to pressure flaking. Heat treatment was documented at MSA levels at Pinnacle Point in South Africa in 2009; and in fact, those scholars (Brown et al.) argued for the existence of the technique by 164,000 years ago.
Sources and Further Information
Mourre V, Villa P, and Henshilwood C. 2010. Early use of pressure flaking on lithic artifacts at Blombos Cave, South Africa. Science 330:659-662.
