The biggest risk of accidentally adding zinc to the alloy is by melting down tire weights. Some are lead alloy, and some are zinc. If there is any doubt I pinch the wheel weight with a pair of side-cutters and see if it leaves a mark. Zinc is a lot harder that lead.
Zinc also melts at a higher temperature than zinc.
PDP aka: Pappy
My Favorites: 22 Hornet and all wildcats, 28-30 Stevens, 32-20 and all wildcats, plus all hyphenated rifle cartridges
Team: "Old Pharts" #348,
Team Winchester #145