[304] Lib. xxxvi. c. 26.
[305] Lib. xxxv. c. 26. and lib. xxxvii. c. 9. The _lapis obsidianus_,
which Obsidius first found in Ethiopia, and made known, is undoubtedly
the same as that vulcanic glass which is sometimes called Icelandic
agate, _pumex vitreus_, and by the Spaniards, who brought it from
America and California, named _galinace_.
[306] Historiæ Augustæ Scriptores, in vita Gallieni, cap. 12.
[307] Ib. in Vopisc. vita Saturnini, c. 8.
[308] Strabo, Amst. 1707, fol. lib. xvi. p. 1099.--Some consider the
glass earth here mentioned as a mineral alkali that was really found
in Egypt, and which served to make glass; but, as the author speaks
expressly of coloured glass, I do not think that the above salt,
without which no glass was then made, is what is meant; but rather a
metallic oxide, such perhaps as ochre or manganese.
[309] Sen. Op. Lipsii, p. 579.
[310] Hist. Nat. lib. xxxvii. c. 12. A passage in Diodorus Siculus,
lib. ii. c. 52, alludes, in my opinion, to this method of colouring by
cementation.
[311] Magia Naturalis. Franc. 1591, 8vo, p. 275.
[312] Kunkel’s Ars Vitraria. Nur. 1743, 4to, pp. 98, 101.
[313] Comment. Soc. Scient. Gotting. ii. p. 41.
[314] Montamy von den Farben zuni Porzellan- und Email-malen. Leipsic,
1767, 8vo, p. 82. Fontanieu, p. 16.
[315] [The extensive use of this substance in colouring glass and
porcelain has rendered its best and most œconomical preparation
a subject of interest both to the chemist and the manufacturer.
Although the determination of its true chemical composition has
presented obstacles almost insuperable, still many important points
with regard to its manufacture have been elucidated. It has been
found that the tin salt used in precipitating it must contain both
the binoxide and protoxide of tin in certain proportions, and it has
been also discovered that the degree of dilution both of the gold
and tin solutions exerts a very perceptible influence on the beauty
of the preparation. Capaun has examined this latter point with great
attention, by testing all the different products as to their power of
colouring glass.
The first point to be attained is the preparation of a solution of
sesquioxide of tin; and for this purpose Bolley proposes to employ the
double compound of bichloride of tin with sal-ammoniac (pink salt).
This salt is not altered by exposure to the atmosphere, and contains
a fixed and known quantity of bichloride of tin, and when boiled with
metallic tin it takes up so much as will form the protochloride;
as the exact quantity of the bichloride is known, it is very easy
to use exactly such a quantity of tin as will serve to form the
sesquichloride. 100 parts of the pink salt require for this purpose
10·7 parts of metallic tin.
Capaun recommends dissolving 1·34 gr. of gold in aqua regia, an excess
being carefully avoided, and diluting the solution with 480 grs. of
water. 10 grs. of pink salt are mixed with 1·07 gr. of tin filings and
40 grs. of water, and the whole boiled till the tin is dissolved. 140
grs. of water are then added to this, and the solution gradually mixed
with the gold liquor, slightly warmed, until no more precipitation
ensues. The precipitate washed and dried weighs 4·92 grs. and is of a
dark brown colour.
M. Figuier states, as the results of his investigations, that the
purple of Cassius is a perfectly definite combination of protoxide of
gold and of stannic acid, or peroxide of tin, the proof of which is,
that it is instantly produced when protoxide of gold and peroxide of
tin are placed in contact.]
[316] The original title runs thus:--De extremo illo et perfectissimo
naturæ opificio ac principe terrenorum sidere, auro, et admiranda ejus
natura, generatione, affectionibus, effectis, atque ad operationes
artis habitudine, cogitata; experimentis illustrata. Hamburgi, 1685,
8vo.
[317] Joh. Molleri Cimbria Literata. Havniæ, 1774, fol. i. p. 88.
[318] Miscellanea Berolinensia, i. p. 94.
[319] The author shows only, in a brief manner, in how many ways this
precipitate can be used; but he makes no mention of employing it in
colouring glass.
[320] I cannot, however, affirm that the _vasa murrhina_ of the
ancients were a kind of porcelain coloured with this salt of gold. This
is only a mere conjecture.
[321] Alchymia Andr. Libavii. Franc. 1606, fol. ii. tract. i. c. 34.
[322] See Gotting. Gel. Anzeigen, 1778, p. 177.
[323] It is well known that Neri’s works are translated into Kunkel’s
Ars Vitraria, the edition of which, published at Nuremberg in 1743,
I have in my possession. The time Neri lived is not mentioned in the
Dictionary of Learned Men; but it appears, from the above edition
of Kunkel, that he was at Florence in 1601, and at Antwerp in 1609.
The oldest Italian edition of his works I have ever seen is L’arte
vetraria--del R. R. Antonio Neri, Fiorentino. In Venetia, 1663. The
first edition, however, must be older. [It is Florence, Giunti,
1612.--ED.]
[324] Neri, b. vii. c. 129, pp. 157 and 174.
[325] Amst. 1651, vol. iv. p. 78. Lewis says that Furnus Philosophicus
was printed as early as 1648.
[326] Glauber first made known liquor of flint, and recommended it for
several uses. See Ettmulleri Opera, Gen. 1736, 4 vol. fol. ii. p. 170.
[327] Lewis, Zusammenhang der Künste. Zür. 1764, 2 vols. 8vo, i. p. 279.
[328] The first edition was printed at Augsburg, in duodecimo, and the
same year at Amsterdam. It has been often printed since, as in 1739, in
3 vols. 4to, without name or place.
[329] A French translation of Orschal and Grummet is added to l’Art de
la Verrérie de Neri, Merret et Kunkel. Paris, 1752, 4to. The editor is
the Baron de Holbach.
[330] See Peter le Vieil’s Kunst auf Glas zu malen, Nuremberg, 1779,
4to, ii. p. 25. This singular performance must, in regard to history,
particularly that of the ancients, be read with precaution. Seldom has
the author perused the works which he quotes; sometimes one cannot find
in them what he assures us he found, and very often he misrepresents
their words.
[331] In what the art of Abraham Helmback, a Nuremberg artist,
consisted, I do not know. Doppelmayer, in his Account of the
Mathematicians and Artists of Nuremberg, printed in 1730, says that
he fortunately revived, in 1717, according to experiments made in a
glass-house, the old red glass; the proper method of preparing which
had been long lost.
[332] Ferber’s Briefe aus Welschland. Prague, 1773, 8vo, p. 114.
[333] The devastations to which the productions of this beautiful art
have been subjected are deeply to be regretted. It appears from the
interesting Account of Durham Cathedral, published by the Rev. James
Raine, that there was much fine stained glass in the fifteen windows of
the Nine Altars which
“shed their many-colour’d light
Through the rich robes of eremites and saints;”
until the year 1795, when “their richly painted glass and mullions were
swept away, and the present plain windows inserted in their place. The
glass lay for a long time afterwards in baskets on the floor; and when
the greater part of it had been purloined the remainder was locked
up in the Galilee.” And in 1802 a beautiful ancient structure, the
Great Vestry, “was, for no apparent reason, demolished, and the richly
painted glass which decorated its windows was either destroyed by the
workmen or afterwards purloined.” The exquisite Galilee itself had been
condemned, but was saved by a happy chance.
[334] In 1774 the French Academy published Le Vieil’s treatise on
Glass-painting. He possessed no colour approaching to red, except the
brick-red or rather rust-coloured enamel subsequently mentioned in the
text, derived from iron.
[335] It appears by a boast of Suger, abbot of St. Denis, which has
been preserved, that the ancient glass-painters pretended to employ
sapphires among their materials; hence, perhaps, the origin of the term
_Zaffres_, under which the oxide of cobalt is still known in commerce.
[336] Oxide of chromium is now substituted for the copper.
[337] That such was the method in use, an attentive examination of
old specimens affords sufficient evidence. One piece that I possess
exhibits large bubbles in the midst of the red stratum; another
consists of a stratum of red inclosed between two colourless strata:
both circumstances plainly point out the only means by which such an
arrangement could be produced.
[338] In 1793, the French government actually collected a quantity of
old red glass, with the view of extracting the gold by which it was
supposed to be coloured! Le Vieil was himself a glass-painter employed
in the repair of ancient windows, and the descendant of glass-painters,
yet so little was he aware of the true nature of the glass, that he
even fancied he could detect the marks of the brush with which he
imagined the red stratum had been laid on!
[339] [M. Langlois names the following writers: “Neri en 1612,
Handicquer de Blancourt en 1667, Kunkel en 1679, Le Vieil en 1774,
et plusieurs autres écrivains à diverses époques, decrivaient ces
procédés.” (p. 192.) He fixes the restoration of the art in France at
about the year 1800, when Brongniart, who had the direction of the
Sèvres porcelain manufacture, worked with Méraud at the preparation
of vitrifiable colours, p. 194. Among modern artists he particularly
mentions Dihl, Schilt, Mortelègue, Robert, Leclair, Collins, and
Willement.]
[340] Bulletin de la Société d’Encouragement pour l’Industrie
Nationale, 1826.
[341] Though it is difficult to produce the copper-glass uniformly
coloured, it is easy to obtain streaks and patches of a fine
transparent red. For this purpose it is sufficient to fuse together 100
parts of crown-glass with one of oxide of copper, putting a lump of tin
into the bottom of the crucible. Metallic iron employed in the same way
as the tin throws out a bright scarlet, but perfectly opake.
[342] “Dr. Lewis states that he once produced a potfull of glass of
beautiful colour, yet was never able to succeed a second time, though
he took infinite pains, and tried a multitude of experiments with that
view.” Commerce of Arts, p. 177.
[343] [At the recent meeting of the British Association for the
Advancement of Science, held at Cambridge (June 1845), M. Splittgerber
exhibited specimens of glass into the composition of which gold entered
as a chloride. These specimens were white, but upon gently heating them
in the flame of a spirit-lamp, they became a deep-red. If again the
same reddened glass is exposed to the heat of an oxygen blowpipe, it
loses nearly all its colours, a slight pinkiness only remaining.]