 |
 |
The photos suggest very much that this has come from the bottom of a cupellation hearth after lead has been removed. It looks as if the piece has been 'poked' on the top surface while still semi-molten, perhaps to push down a blister. The groove has probably been left by the last of the litharge meniscus before it disappeared. One would expect a piece like this to be circular in plan if the furnace bottom were smooth, however in an industrial process the hearth bottom would have been irregular. The weight was nearly 14 ounces which sggests that very little lead had been processed. A refinery with a Pattinson process would normally treat down to about 4 oz/ton of lead (lead having 2 oz/ton would not be treated). This means that the silver came from not more than 3.5 tons of lead. The silver-rich mines of the N. Pennines were 8-10 oz/ton silver, equivalent to a weight of lead of 1.5 tons. I don't know how much lead would have been cupelled in a single charge but presumably more was added once some had oxidised. Trace analysis might help but most of the impurities would have gone with the litharge during refining or even before that if Pattinsonising had been used. Richard ----- Original Message ----- From: "Thompson, Woodrow B." <[log in to unmask]> To: <[log in to unmask]> Sent: Thursday, March 18, 2010 2:19 PM Subject: Re: Silver There's also an odd groove around the perimeter of the specimen. -----Original Message----- From: mining-history [mailto:[log in to unmask]] On Behalf Of Keith Nicholls Sent: Thursday, March 18, 2010 10:05 AM To: [log in to unmask] Subject: Re: Silver Looks to me like there is some more to the stamp mark - to the left of the letter R, been worn away Keith -----Original Message----- From: mining-history [mailto:[log in to unmask]] On Behalf Of Thompson, Woodrow B. Sent: 18 March 2010 02:02 PM To: [log in to unmask] Subject: Re: Silver The piece looks so pure that a specific gravity measurement should be easy and perhaps diagnostic. The shape is curious. It looks stream-rounded, and yet the stamp marks have not worn off. Perhaps they survived because of having been deeply incised. -----Original Message----- From: mining-history [mailto:[log in to unmask]] On Behalf Of Tim Young Sent: Thursday, March 18, 2010 9:40 AM To: [log in to unmask] Subject: Re: Silver I see this find is already pictured on the internet at: http://metaldetectingforum.com/showthread.php?p=475325 and has already been reported to the authorities. I assume it has been correctly identified - I've seen waterworn blocks of aluminium that look quite like this (quite common where joy riders dump cars into streams!!). Tim -- Dr Tim Young Email: [log in to unmask] Web: www.geoarch.co.uk Phone: 029 20881431 Mobile: 07802 413704 Fax: 08700 547366 This email has been scanned for viruses by Netshield MXSweep. Geotechnics Limited, Registered in England No. 1757790 at The Geotechnical Centre, 203 Torrington Avenue, Tile Hill, Coventry CV4 9AP www.geotechnics.co.uk