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I'm trying to learn flint knapping, and I keep seeing references to abrading the edge while working the material.

What is the purpose of doing this? How do I know when an edge should be abraded, and how do I know when I have abraded it sufficiently to go back to pressure flaking?

Beofett
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    @Willeke -- I was sort of torn about your edit, but it includes a partial answer (abrading is done "to strengthen the [edge] in preparation for flake removal") and I think it would be better added as an answer. – Erica Feb 12 '17 at 13:40

1 Answers1

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The purpose is to prepare a flake for improved manipulation.

Abrasion is a process also referred to as 'raking':

Raking is the action of carefully dragging a course abrader or other device to remove "micro" flakes from the edge of a biface or preform to change it's [sic] shape or give support to an edge before actual abrading is done prior to percussion or pressure work.
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Edges being worked [especially while soft hammer knapping] must be ground dull prior to flake removal. This dulling helps prevent edge collapse. A piece of sandstone, very soft limestone, or other soft rock may be used to dull the edge.
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The process [of lithic reduction] also involves frequent preparation of the edge to form better platforms for pressing off flakes. This is usually accomplished with abraiders made from a coarse-grained stone such as basalt or quartzite.
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Essentially, the abrasion allows for the force to be distributed more evenly and controllably.

Joachim
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