This discussion interests us here for our own preoccupations in early
metallurgy, and we have two questions :
- what are the written sources for these figures and process descriptions,
and how may one deduce such precise percentages from these documents ;
- have there been any recent experimentation works following archaic
processes, accompanied by archaeometric protocols (raw material and
resulting matter analysis)
Best wishes
Ian Cowburn, Bruno Ancel
CCSTI L'Argentière-la-Bessée
Le 1/12/04 0:28, « Peter Claughton » <[log in to unmask]> a écrit :
> At 22:48 30/11/04 +0100, rdn wrote:
>> Please download this image (122kByte) for a photo (cupel) and text about
>> cupellation.
>>
>> http://users.pandora.be/rdn/digifoto/evaluate/cuppel1.jpg
>
> The cupel and description on the site above were for assay or metal working
> purposes. Large scale silver refining, in conjunction with ore processing
> (smelting) in association with mining sites would have used much larger
> cupels. The data in Agricola (central Europe in the 16th century) suggests
> cupels in the order of 0.75 metres in diameter and cupels recovered from
> the Roman period site at Brompton / Pentrehyling on the Shropshire /
> Montgomeryshire border were around 0.5 metres diameter. Judged on the
> limited documentation available, cupels of similar dimensions were probably
> used in the English silver mines of the 14th century.
>
> Very little of the total amount of lead oxidised in these large scale
> processes was actually absorbed into the cupel lining; the majority was
> removed as litharge which was then resmelted to recover the lead. Some lead
> was, of course, lost in the process (losses could be up to 28 per cent in
> the early 14th century mines) and this had to be balanced against the value
> of the silver recovered.
>
> When working ores at around 125 ozs per ton of lead metal in the late
> medieval period the value of the lead lost was insignificant compared with
> the high value of the silver recovered. But it was a different matter for
> ores much lower in silver and, as the price of lead rose comparible with
> the price of silver after 1500, the level at which silver might be
> recovered economically rose. It wasn't until the development of enrichment
> processes, eg. Pattinsons, in the mid 19th century that the recovery of low
> levels of silver (even as low as 2-3 ozs / ton) was economic - but then the
> lead loss in refining was largely confined to the final cupellation of a
> very silver rich lead metal.
>
> Peter
>
> ______________________________________________
>
> Dr Peter Claughton,
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>
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