What's this left on my gauze?

[_space_cadet_]

Smoking crack and heroin on the same pipe, small metal hash pipe I think, (I know, I know, should have separate pipes!) using gauze (wire wool type stuff.) Sometimes, there is a residue left on the gauze that can be lit multiple times, and still produce lots of smoke, tastes vaguely of both. Is this harmful or is it just leftovers on there? It seems to be a lot of smoke, and like I said can be lit and inhaled numerous times, which I find strange.

Any ideas guys?