Primitive Archer
Main Discussion Area => Flintknapping => Topic started by: Jodocus on November 04, 2014, 04:34:29 pm
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Bulbs are annoying. >:(
When I spall, I need to chip off the bulb afterwards.
When I pressure, the bulb is the main cause of witdth loss.
What determines the size of it? can I minimize it?
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There's more knowledgeable fellers than me, but I remember on a discussion of hammerstones that the harder the stone, the generally bigger the bulb of percussion. If you are using a solid copper bopper, you may want to switch to a lead filled copper cap bopper. If you are using antler, I don't know...Other than that, all I would know to comment on is to make your platforms closer to the edge and prepare the edge well. If you get a lot of "meat"on your hit and are striking too far below the platform, you can get bigger bulbs too. You may also be able to reduce the thickness of bulbs by striking at a greater angle - remember that hertzian cone thing - the straighter you strike in, the more of the cone (bulb) will be in your core.
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Ya, the density on your percussion tool, be it hammerstones, antler, wood, or copper, is a big factor. As well as things like speed, platform prep, and where you strike it. I generally prefer larger antler billets with lightly ground platforms struck fairly quickly as low on the edge as possible. Since antler 'grabs' the edge well, I get minimal bulbs this way. If I have a rock too big for my antler tools I use a slightly soft hammerstone with the same strategy, but I grind the platforms a little more.
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It is very possible to minimize the bulb size. Try striking flakes off a large core and use a "swiping" motion when hitting the edge.
If you hit into the stone, instead of glancing blow, the flake will have a large bulb or will create a step fracture.
Striking flakes off a large core also helps because the extra mass gives you more power in your strike (the mass resists the strike instead of backing away from it) and allows you to focus less on the intensity of the swing and more on the accuracy of the swing.
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Thank you guys, I'll try it out today. Of course, large cores are a little more difficult to come by.
Does this also apply to pressure flaking? I usually use a copper flaker, but I have one of bone (even though I'm not sure bone is softer than copper?)
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A few post back, someone gave this advise... Make the bulb end the pointy end of your point. If I remembered who posted this, I would give them the credit for the idea. I always went about it the other way, but this makes good sense.
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Hey Jodcus - I don't know how one achieves big bulbs on pressure flakes, but I do know the more pointy the flaker, the larger the bulb to some degree. I'd say all the same theories apply as above (sorta). Make sure you grind or sufficiently prepare the edge and are removing flakes BELOW the center line - that's the main thing for pressure flaking.
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If I want to get rid of a big bulb, I reduce the wattage.
Say from a 100 w bulb to a 40w bulb.
Actually the replies here are terrific. One thing though--
Do you reduce the overall size of the spall if you are able to
reduce bulb size. Err a thin/thickness sort of thing.
Zuma