im going through glass like a mad man and all i seem to be doing is getting crappy little flakes...
show us the glass and the tool you're working with. also, show us an edge that you've worked.
from what i've found in my experience (which is minimal), is that some glass knaps differently than others. and when you get to working bottle bottoms, the concave/convex surfaces add another dimension of complexity.
keep at it though, because your technique will come with a little perseverance.
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Before long those little flakes will get bigger,and bigger. Before long you'll be over running those flakes.
i can't stand it when that happens. i've lost a few points that way.