Building blades that look sharp?

I've been working on a spear, but this question I am sure will also apply to swords etc.

I've built up the basics of the spear, but the blade part of it... just doesn't look sharp.. someone mentioned to me to use spheres, but didn't explain much beyond that.

How do I make a blade look sharp?? As in cutting - sharp, not cool - sharp.... ???

I think you can use a flattened "ring". After some "cutting" it will give a sharp edge. Experiment there.