I wonder if this was from a test of a batch of lead for silver content.
Lead was generally given mark letters for a batch of 400 pieces (400
pieces = 1 Mark).
No idea of whether it would be batch R or batch M
If as Richard says it is from a relatively small amount of lead, would they
sample a batch or batches in this way?
In a message dated 18/03/2010 16:40:47 GMT Standard Time,
[log in to unmask] writes:
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
--
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