Robert
I have not seen anything like the baffles you describe, but they would provide a larger surface area for any solids in the flue gases to precipitate out on so, if the flues were intended to remove particulates from the discharge fumes, the addition of baffles would make the process more efficient. I was surprised to see you describe the lead-rich deposit as a hard glaze. Was it really vitreous, as this would require a far higher temperature than I would expect to find in a flue/chimney. Lead glazes mature at about the same temperature at which earthenware is fired (?700+ degreesC). what is more likely is a massive deposit of oxides precipitating from the flue gases as they cool.
There are records of boys being sent into the flues of post-medieval smelters in England when they were cold to sweep out the fumes which deposited on the walls.
Justine
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Justine Bayley
English Heritage Centre for Archaeology
Fort Cumberland, Fort Cumberland Road, Eastney
Portsmouth PO4 9LD
Phone: 02392-856794
Fax: 02392-856701
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