down some of the powdered charcoal into it from the wall, so that the slags
may be separated from the hot metal, and so that it may be covered, lest
any part of it, being very hot, should fly away with the fumes. If after
the slag has been skimmed off, the powder does not cover up the whole of the
tin, the smelter draws a little more charcoal off the wall with a scraper. After
he has opened the tap-hole of the forehearth with a tapping-bar, in order
that the tin can flow into the tapping-pot, likewise smeared with lute, he
again closes the tap-hole with pure lute or lute mixed with powdered charcoal.
The smelter, if he be diligent and experienced, has brooms at hand with which
he sweeps down the walls above the furnace ; to these walls and to the
dust chamber minute tin-stones sometimes adhere with part of the fumes.
If he be not sufficiently experienced in these matters and has melted at the
same time all of the tin-stone,—which is commonly of three sizes, large,
medium, and very small,—not a little waste of the proprietor's tin results ;
because, before the large or the medium sizes have melted, the small have either
been burnt up in the furnace, or else, flying up from it, they not only adhere to
the walls but also fall in the dust chamber. The owner of the works has
the sweepings by right from the owner of the ore. For the above reasons
the most experienced smelter melts them down separately ; indeed, he
melts the very small size in a wider furnace, the medium in a medium-sized
furnace, and the largest size in the narrowest furnace. When he melts down
the small size he uses a gentle blast from the bellows, with the medium-sized
a moderate one, with the large size a violent blast ; and when he smelts
the first size he needs a slow fire, for the second a medium one, and for the
third a fierce one ; yet he uses a much less fierce fire than when he smelts
the ores of gold, silver, or copper. When the workmen have spent three
consecutive days and nights in this work, as is usual, they have finished
their labours ; in this time they are able to melt out a large weight of small
" the dried beds of torrents. The miners wash these sands, and that which settles they heat
" in the furnace. It is also found in gold mines, which are called alutiae. A stream of water
" passing through detaches small black pebbles variegated with white spots, the weight of
" which is the same as gold. Hence it is that they remain in the baskets of the gold collectors
" with the gold ; afterward, they are separated in a camillum and when melted become white
'* lead."
There is practically no reference to the methods of Cornish tin-working over the whole
period of 2,000 years that mining operations were carried on there prior to the Norman
occupation. From then until Agricola's time, a period of some four centuries, there are
occasional references in Stannary Court proceedings, Charters, and such-like official documents
which give little metallurgical insight. From a letter of William de Wrotham, Lord Warden
of the Stannaries, in 1198, setting out the regulations for the impost on tin, it is evident that
the black tin was smelted once at the mines and that a second smelting or refining was carried
out in specified towns under the observation of the Crown Officials. In many other official
documents there are repeated references to the right to dig turfs and cut wood for smelting
the tin. Under note 8, p. 282, we give some further information on tin concentration, and
the relation of Cornish and German tin miners. Biringuccio (1540) gives very little information on tin metallurgy, and we are brought to De Re Metallica for the first clear exposition.
As to the description on these pages it must be remembered that the tin-stone has been
already roasted, thus removing some volatile impurities and oxidizing others, as described
on page 348. The furnaces and the methods of working the tin, here described, are almost
identical with those in use in Saxony to-day. In general, since Agricola's time tin has not seen
the mechanical and metallurgical development of the other metals. The comparatively
small quantities to be dealt with ; the necessity of maintaining a strong reducing atmosphere,
and consequently a mild cold blast ; and the comparatively low temperature demanded,
gave little impetus to other than crude appliances until very modern times.
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