Sharp edges are, as mentioned, better left to other materials.
GS works like taffy and cures like rubber - fine for more organic shapes, but it makes sculpting a sharp edge pretty much impossible, outright, and it doesn't take well to filing or sanding. There are a number of putties that work more like clay and cure more like hard plastic or porcelain, which makes for better initial definition while sculpting and allows you to refine the shape post-cure with abrasives. To get something in the middle, you can mix putties, like Johnno does. If you look at the "greens" of professional sculptors, you'll usually see varying shades of green, as well as occasional bits of brown or other colors - that's a result of varying the
GS mix ratio, including additives, and using other putties, altogether, depending on the task at hand. The fact that weapons and the like are usually some other color should be a decent indication of the limitations of
GS.
As far as fine detail is concerned, a variety of fine-
tipped (note that the entire head needn't necessarily be small - a kitchen knife would be unwieldy, but may have as fine a point as your hobby knife) sculpting tools certainly helps, but it mostly comes down to skill. Luckily, for those of us without an inordinate amount of talent, there's practice.
There are other important tidbits, like lubricating your tools, working at the most suitable point in the cure, and working in layers, but those have been covered ad nauseum in more general
GS primers, if you don't already know them. Then again, so has much of what I've already said... Guess I'm finished, then.
