Nonmetallic flux residue that forms on certain welds and is normally removed from the weld bead after solidification.
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Meaning and boundaries
Material ejected as hot metal droplets toward glass is weld spatter, not slag. A GlassRenu page should use slag only when flux-derived slag actually reaches the glass.
Why it matters in glass restoration
Correct terminology improves search accuracy, source credibility, technician communication, and the diagnosis of embedded metal versus surface residue.