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Book XII: Solidified Juices

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day, as much as in ancient times, there exists the belief in the singular
power of the latter to attract to itself the vitreous liquid just as it does iron,
and by attracting it to purify and transform green or yellow into white ; and
afterward fire consumes the magnes. When the said juices are not to be had,
two parts of the ashes of oak or holmoak, or of hard oak or Turkey oak,
or if these be not available, of beech or pine, are mixed with one part
of coarse or fine sand, and a small quantity of salt is added, made from salt
water or sea-water, and a small particle of magnes ; but these make a less
white and translucent glass. The ashes should be made from old trees, of
which the trunk at a height of six feet is hollowed out and fire is put in, and
thus the whole tree is consumed and converted into ashes. This is done in
winter when the snow lies long, or in summer when it does not rain, for the
showers at other times of the year, by mixing the ashes with earth, render
them impure ; for this reason, at such times, these same trees are cut up
into many pieces and burned under cover, and are thus converted into ashes.
Some glass-makers use three furnaces, others two, others only one.
Those who use three, melt the material in the first, re-melt it in the second,
" magnes, because of the belief that it attracts liquefied glass as well as iron. In a similar
" manner many kinds of brilliant stones began to be added to the melting, and then shells
" and fossil sand. Authors tell us that the glass of India is made of broken crystal, and
"in consequence nothing can compare with it. Light and dry wood is used for fusing,
" cyprium (copper ?) and nitrum being added, particularly nitrum from Ophir etc."
A great deal of discussion has arisen over this passage, in connection with what this
lapis magnes really was. Pliny (xxxvi., 25) describes the lodestone under this term, but
also says : " There (in Ethiopia) also is haematites magnes, a stone of blood colour, which
" shows a red colour if crushed, or of saffron. The haematites has not the same property of
" attracting iron as magnes." Relying upon this sentence for an exception to the ordinary
sort of magnes, and upon the impossible chemical reaction involved, most commentators
have endeavoured to show that lodestone was not the substance meant by Pliny, but
manganese, and thus they find here the first knowledge of this mineral. There can be
little doubt that Pliny assumed it to be the lodestone, and Agricola also. Whether the
latter had any independent knowledge on this point in glass-making or was merely quoting
Pliny—which seems probable—we do not know. In any event, Biringuccio, whose work
preceded De Re Metallica by fifteen years, does definitely mention manganese in this
connection. He dismisses this statement of Pliny with the remark (p. 37-38) : " The
" Ancients wrote about lodestones, as Pliny states, and they mixed it together with nitrum
in their first efforts to make glass." The following passage from this author (p. 36-37),
however, is not only of interest in this connection, but also as possibly being the first specific
mention of manganese under its own name. Moreover, it has been generally overlooked
in the many discussions of the subject. " Of a similar nature (to zajfir) is also another
" mineral called manganese, which is found, besides in Germany, at the mountain of
" Viterbo in Tuscany . . . it is the colour of ferrigno scuro (iron slag ?). In melting it
" one cannot obtain any metal . . . but it gives a very fine colour to glass, so that the
" glass workers use it in their pigments to secure an azure colour. ... It also has such
*' a property that when put into melted glass it cleanses it and makes it white, even if it were
" green or yellow. In a hot fire it goes off in a vapour like lead, and turns into ashes."
To enter competently into the discussion of the early history of glass-making would
employ more space than can be given, and would lead but to a sterile end. It is certain
that the art was pre-Grecian, and that the Egyptians were possessed of some knowledge of
making and blowing it in the XI Dynasty (according to Pétrie 3,500 b.c.), the wall
painting at Beni Hassen, which represents glass-blowing, being attributed to that period.
The remains of a glass factory at Tel el Amarna are believed to be of the XVIII
Dynasty. (Pétrie, 1,500 b.c.). The art reached a very high state of development among
the Greeks and Romans. No discussion of this subject omits Pliny's well-known story
(xxxvi. 65), which we also add : " The tradition is that a merchant ship laden with
" nitrum being moored at this place, the merchants were preparing their meal on the beach,
" and not having stones to prop up their pots, they used lumps of nitrum from the ship,
" which fused and mixed with the sands of the shore, and there flowed streams of a new
" translucent liquid, and thus was the origin of glass."
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