Knapping is a fascinating skill and hobby. In case you are unaware of what it is, “knapping” is the act of chipping away at a piece of material (often flint–hence the common “flintknapping,” chert, or obsidian) through a process known as lithic reduction. What on earth is that, you ask? Wikipedia describes it as:
Lithic reduction involves the use of a hard hammer percussor, such as a hammerstone, a soft hammer fabricator (made of wood, bone or antler), or a wood or antler punch to detach lithic flakes from a lump of tool stone called a lithic core (also known as the “objective piece”). As flakes are detached in sequence, the original mass of stone is reduced; hence the term for this process. Lithic reduction may be performed in order to obtain sharp flakes, of which a variety of tools can be made, or to rough out a blank for later refinement into a projectile point, knife, or other object. Flakes of regular size that are at least twice as long as they are broad are called blades. Lithic tools produced this way may be bifacial (exhibiting flaking on both sides) or unifacial (exhibiting flaking on one side only).
There are a ton of knapping videos on YouTube and numerous written tutorials online. My favorite videos are often the ones where people challenge themselves to knap a material that doesn’t work very easily. Glass flakes reasonably well, but it’s obviously extremely fragile and prone to unwanted cracking and fractures.
In this video, bushcrafting ‘tuber and self-described “historical hunter,” Shawn Woods, goes about trying to turn an old whiskey bottle, which carries the ominous warning “Federal Law Forbids Re-Use of This Bottle,” into six glass arrowheads. In the video, he explains the origins and reasons for this warning found on old liquor bottles.
You’ll notice that he uses the term “flintknapping,” when he’s actually napping glass. It is common to use napping and flintknapping interchangeably, even when materials other than flint are used. Language is promiscuous.