Friday, January 11, 2013

The Green Monster de Pachuca

Hey everyone!

The winner of the first giveaway is Lisa Marie Shillito Roberts!!! 

I'll get in touch about your address.

today I had an interview with an obsidian from Pachuca in the central highlands of Mexico!

The monster lives!
Pachuca obsidian has bested me on several fronts over the course of the last few years.  My first run in with this stone ended in several broken points after I bummed some off the other Field Supervisor, Rob Jones, at the Mule Creek Archaeological Fieldschool last year (sorry I busted your stuff).  I also use this obsidian as a geological standard for X-ray florescence analyses at the Center for Chemical Characterization Lab at Texas A&M University.  By tracking relationships within tool source distribution we can target questions about subsistence practice, adaptive strategies during environmental change, social relationships and changing social landscapes over time.

Pachuca on left, Glass Buttes, Oregon on right
Perhaps the attraction comes from the olive green color of the material, or maybe the nuances it holds as a material, probably both.  Simply put, Pachuca obsidian is beautiful and difficult.  I suppose sometimes those two things become complimentary and endearing. Pachuca obsidian is an elegant stone; it forces the use of specific tools, novel approaches and a patient mind.
Central Mexico, southern Idaho, central Oregon

This material seems to step fracture more often than other volcanic glasses, meaning that the slightest pressure against a poorly-created flaking platform will result in a lumpy bifacial blade.  I don't use copper tools for shaping stone anymore and personally like little traits that antler pressure flaking makes.  Antler tines flex with pressure and allows the release of longer flakes with shallower negative flake scars along the blade edge.  Antler tines let the stone bite in a bit as you're building up pressure to detach. Smaller platforms allow thinner, finer flake detachment as there is less mass to move from the onset.  I chose to make longer, thin platforms high upon the working edge.     
Here's the working edge with circles showing different platforms angles, depths and widths

All obsidians have their own personality when it comes to pressure flaking.  Some sources are brittle yet easy to flake and end in blended flake scars.  Others are more plastic and give raised flakes scar margins.  Mixing a more plastic material with the traits of copper pressure flaking will give pronounced flake scar definition and is good when trying to display unique flaking patterns.  Less plastic materials flaked with an antler tine will give smooth, blended shapes that are sleek and utilitarian. 

large flake removal to under-cut a stack on the other edge
Mind the Stacks, Dear

This stuff is a lot of fun to play with once you figure out the best angles.   I crushed a ton of flake  platforms on this pachuca obsidian.  multiple failed attempts to fix this problem create "stacks" on the face of the blade.  These features are often a signal of an incorrect combination of platform strength, removal angle and applied force during flake removal.  Poor flaking quality of a stone will also make this happen a lot.  Still, I create these flaws all the time and have only recently been able to make flakes that can fix the situation.  A stack as a funny thing.  These features on the landscape of a biface are created by repeated attempts to remove the evidence of what was initially a small mistake with improper stabs at a fix.  A stack in the wrong place means that the blade you have created will not integrate  uniformly into the haft and may form a point of weakness along the cutting edge.
Finished project

 Stack on a point from the mid Archaic ca. 4,000 yrs
The lesson of Pachuca obsidian illustrates that unmodified challenges to a steady state create like consequences.  when current flaking strategies fail on this material...logically I need to weigh the benefits of alternative approaches lest I compound the issue.  This glass ended up needing a thin and sharp antler tine for good flex combined with lower platform angles with wider, shallower platform surfaces.   

The stack was approached from both sides but held fast
Creating a stack on a biface always commands an annoyingly haunting level of metaphorical significance.  The tangible features are created as the result of an initial hasty decision.  With an unchanged approach, repetition allows a series of uncalculated flakes to become undeniable.  A self-loathing mind might be troubled by  traces of past mistakes manifested, a red-handed reflection of poor life choices.  I of course have never, not even once felt this way and can barely even describe it decently.                   

But you know what? There's actually an easy fix!  If you create a deep platform on the opposite margin you can undercut the whole mess from the other side with an overshot flake.  So it's not at all doom and gloom by any means.  An assessment of the problem and preparation for a solution will fix it up in no time flat. The blade will haft (yeah made a verb out of that) and your cutting edges will be back to uniform before you know it.  fixing a stack has actually become one of my favorite little things to do while making a biface. 

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