SILVER AND LEAD
In prehistoric Europe, silver and lead are not, in general, prior to La Tene
period (300 BC).
Silver and lead were closely related, since both were derived from the same mineral, galena. This is a lead sulfide ore, which usually contains a small percentage of silver. Galena is very common and is often associated with copper ores.
The production of silver and lead introduced into general metallurgy processing methods and the cupellation of sulphides.
The processing of the crystal consists of a partial desulphurization by roasting, followed by the reduction of the product obtained and that the litharge (lead oxide).
A simple open hearth furnace was sufficient. The fuel and ore were mixed together, or stacked in alternating layers. A natural or artificial draft provided the necessary air.
Part of the sulfur in the form of sulfur dioxide evaporates, but some remained in the form of galena unprocessed which has lead sulfate.
Reached the necessary degree of desulfurization, the temperature was increased, and the lead oxide, sulphate of lead and galena reacted to form the lead, that was collected at the bottom of the oven, while sulfur residue is evaporated in the form of sulfur dioxide. The charcoal added as fuel, preventing re-oxidation
The final product was an alloy of lead-silver hardest of hard lead, it contained many impurities, such as antimony, copper, tin and arsenic.
This ancient process brought together the two modern phases of roasting and reduction.
Although the technique was relatively simple, chemical reactions were correspondingly complex and the old metalworker did not have the appropriate knowledge to control them.
The copper in the native
state, which is located in the Po valley, has the structural form of small flakes ,
occasionally granules and very rarely large masses. In (river)bed of
mountain torrents, where often there is gold, are sometimes
found green-purple and
with a copper core in
the native state.
These nodules are very hard to work, however the metal in its native state is also found in thin layers and dendritic forms that are much more workable.
With the discovery of the recook, which eliminates the embrittlement caused by cold working, it could be possible to use more hard nodules to prepare enough large ingots.
The typical microstructure of copper in its native
state has been found in several very ancient objects in the Danube valley.
The first classed copper minerals (cuprite, malachite, azurite) includes carbonates and oxides. They can easily be reduced to metal by heating with charcoal. The second class of minerals (ie calcosite, chalcopyrite, bornite, covellite) contains sulfur compounds of copper, sometimes mixed or combined with other metals or metalloids, such as iron, antimony and arsenic. This class is more common than before and generally is found in deeper deposits.
The metallurgist. about
to perform an approximately complete
extraction from sulphide ores, he must have had recourse to
various stages of recast with coal
and fusion in a current of air.
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last review 14/11/2012