"David R. Birch" fired this volley in news:j29vda01oj2
@news6.newsguy.com:

You can argue with my dictionary, which gives the first definition of
slag as "the dross or scoria of a metal".

Such dross shows up in the smelt. Finished metallurgical alloys scale
slightly when heated to welding temperatures. Slag does not form except in
the situation where lots of impurities are present -- such as a welding
flux.

This is a metal-working sig. Common use in a field often does not match
what Webster's might say is common use among the populace.

LLoyd