Visited the old ironworks museum in Pittsburgh and saw something cool about forge welding

Luna Grant · 2026-03-28T14:55:09.104437+00:00

I was at the Carrie Blast Furnaces site last weekend, checking out the historic forges. One display showed how they used to weld large iron beams back in the day. They had a simple clay paste mix in a bucket next to the anvil, labeled as a flux recipe. The guide said they'd throw a handful of that clay into the fire right before pulling the metal to weld. It made a big, bubbly barrier that kept the air out way better than just borax alone. I tried a small batch at my shop yesterday with some local red clay and a bit of fine sand. The weld on a test piece of mild steel was super clean, with almost no scale. Has anyone else experimented with old school clay fluxes like that? I'm curious if different clay types work better.

diana_grant6mo ago

Doubt it's that big a deal, @thea_anderson82.

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thea_anderson826mo ago

Interesting! I've only ever used borax, but that clay trick sounds like it's worth a try.

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flores.emma5mo ago

Oh neat, I actually read something about that in an old blacksmithing forum a while back. Some folks swear by using local clays as flux, saying it's all about the silica content in the sand you mix in. I'd be curious how a pure kaolin clay would compare, but your results sound solid.

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