The name cobalt is given at present to that metal and its ores, the
oxides of which are largely employed in the manufactures of glass,
porcelain and pottery, for the production of a blue colour. The
cobalt ores are first roasted and freed from foreign mineral bodies,
particularly sulphur, iron, nickel, bismuth, and arsenic, with which
they are united, and then well calcined, and sold, either mixed or
unmixed with fine sand, under the name of zaffer (_zaffera_); or the
cobalt is melted with siliceous earth and potash to a kind of blue
glass called smalt, which, when ground very fine, is known in commerce
by the name of powder-blue. All these articles, because they are most
durable pigments, and those which best withstand fire, and because
one can produce with them every shade of blue, are employed, above
all, for tinging crystal and for enamelling; for counterfeiting opake
and transparent precious stones, and for painting and varnishing real
porcelain and earthen and potters’ ware. This colour is indispensably
necessary to the painter when he is desirous of imitating the fine
azure colour of many butterflies and other natural objects; and the
cheaper kind is employed to give a blueish tinge to new-washed linen,
which so readily changes to a disagreeable yellow.
The preparation of this new colour may be reckoned among the most
beneficial inventions of modern times. It rendered of importance an
useless and hurtful production; gave employment to a number of hands;
assisted in bringing many arts to a degree of perfection which they
could never before attain; and has drawn back to Germany a great deal
of money which was formerly sent out of it for foreign articles.
Though there is no doubt that the process used in the preparation of
cobalt and smalt was invented about the end of the fifteenth or the
beginning of the sixteenth century, we have reason to ask whether the
ancients were acquainted with cobalt, and if they employed it for
colouring glass. They opened and worked mines in various parts; and
it is at any rate possible that they may have found cobalt; they made
many successful attempts to give different tints to glass[1472]; and
they produced blue glass and blue enamel. They may have learned by an
accident to make this glass, as they did to make brass; and they may
have continued to make the former as long as their supply of coloured
earth lasted. When the mineral failed them, they may have lost the art,
in the same manner as the method of preparing Corinthian brass[1473]
was lost for a considerable space of time. The use of cobalt does not
imply a knowledge of its metal; for the moderns made brass and smalt
for whole centuries, before they learned to prepare zinc and regulus of
cobalt.
It seems, however, difficult to answer this question; for one can
scarcely hope to discover cobalt with any certainty among those
minerals mentioned by the ancients. They could describe minerals in no
other manner than according to their exterior appearance, the country
where they were found, or the use to which they applied them. Now
there is no species more various and more changeable in its figure and
colour than cobalt ore, which on this account shows the impossibility
of distinguishing minerals with sufficient accuracy by external
characteristics. Besides, there are scarcely two passages of the
ancients which seem to allude to it; and these, when closely examined,
give us little or no information.
The meaning of the term _cadmia_ is as various and uncertain as
that of the word _cobalt_ was two centuries ago. It signified often
calamine; sometimes furnace-dross; and perhaps, in later times, also
arsenic; but, as far as I know, it was never applied to cobalt till
mineralogists wished in modern times to find a Latin term for it[1474],
and assumed that which did not belong properly to any other mineral.
The well-known passage of Pliny[1475], in which Lehmann thinks he
can with certainty distinguish cobalt, is so singular a medley that
nothing to be depended on can be gathered from it. The author, it is
true, where he treats of mineral pigments, seems to speak of a blue
sand which produced different shades of blue paint, according as it
was pounded coarser or finer. The palest powder was called _lomentum_;
and this Lehmann considers as our powder-blue. I am however fully
convinced that the _cyanus_ of Theophrastus, the _cæruleum_ of Pliny,
and the _chrysocolla_[1476], were the blue copper earth often already
mentioned, which may have been mixed and blended together. Besides,
Pliny clearly adds to it an artificial colour, which in my opinion was
made in the same manner as our lake; for he speaks of an earth, which
when boiled with plants, acquired their blue colour, and which was
in some measure inflammable. With these pigments walls were painted;
but as many of them would not endure lime, they could be used only on
those which were plastered with clay (_creta_). The expression _usus
ad fenestras_ has been misapplied by Lehmann, as a strong proof of his
assertion; for he explains it as if Pliny had said that a blue pigment
was used for painting window-frames; but glass windows were at that
time unknown. I suspect Pliny meant to say only that one kind of paint
could not be employed near openings which afforded a passage to the
light, as it soon decayed and lost its colour. This would have been the
case in particular with lake in which there was a mixture of vegetable
particles.
For my part, I find in this passage as few traces of smalt as M.
Gmelin; and I agree with him in opinion that the strong and unpleasant
mixtures arising from cobalt would, had it been known, have induced
the ancients to make particular mention of it in their writings.
Would not the arsenic, which is so often combined with cobalt, have
given occasion to many reports respecting the dangerous properties of
these minerals? And would not arsenic and bismuth have been sooner
known, had preparations of cobalt been made at so early a period? It
is a circumstance of great weight also, that in the places where the
ancients had mines, and where antiquities painted or tinged blue, and
resembling in colour that produced by cobalt, have been dug up, cobalt
has not been discovered, or has been discovered only in modern times.
At present we know nothing of Egyptian, Arabian, Ethiopian, Italian,
and Cyprian cobalt; and in Spain[1477] this mineral was first found in
the reign of Philip IV. I shall here observe, that the island of Cyprus
was formerly so abundant in copper, that, in a mineralogical sense, it
might be called the island of Venus; and we can therefore entertain the
less doubt that the _cæruleum Cyprium_ was copper-blue.
The principal reason, however, why Lehmann, Pauw[1478], Ferber,
Delaval, and others, think that the ancients used smalt, and were
acquainted with cobalt, is that, as has been already said, various
antiquities both of painting and enamel have been discovered, in which
a blue appears that seems to give grounds for conjecturing that it
was produced by cobalt. Ferber[1479] speaks of blue glass squares in
mosaic-work; and Delaval mentions old Egyptian glass-work of this
colour[1480]. It is well known also that the Chinese and people of
Japan gave to their porcelain that fine blue colour, for which it is
celebrated, long before the discovery of smalt in Europe. On mummies
a blue is seen likewise, which, even after so many centuries, seems
to have lost little or nothing of its beauty[1481]. We must therefore
allow that the ancients used either ultramarine or cobalt.
The first opinion seems, in regard of porcelain, to be confirmed
by Duhalde[1482], who speaks of a mine of _azur_, and relates that
the Chinese, in modern times, use instead of it, for painting their
porcelain, a blue colour brought from foreign countries. It is probable
that by the former he means lapis lazuli, and by the latter smalt,
which is sent in large quantities from Europe to China. The invention
of ultramarine, however, appears to me too new, its effect on porcelain
too uncertain, and its price too high to allow us to suppose that
it has been much used. We should therefore have been almost obliged
to adopt the latter opinion, had not M. Gmelin proved by chemical
experiments[1483] that it is not only possible to give to glass and
enamel a blue colour by means of iron, but that the before-mentioned
antiquities, upon which so much stress has been laid, show not the
smallest traces of cobalt. He even made experiments upon blue tiles,
found in a Roman tessellated foot-pavement at Montbeillard; and
likewise on the blue paint of the mummy which was presented to our
university by the king of Denmark[1484]. He has also mentioned various
articles on which a blue colour is produced by the vitrification of
iron. Of this nature are in particular those slags found near the
smelting-houses at the iron-mines of the Harz forest; and I myself have
seen slags which were of a blue colour exceedingly beautiful. Volcanic
slags, or scoriæ, found in the neighbourhood of Verona, Vicenza, and
other parts of Italy, are mentioned also by Ferber[1485], which seems
to confirm the conjecture of Dr. Bruckmann[1486], that the ancients
may have used such slags for their works. It is probable that the
ancients were first induced by the blue slag of their smelting-houses
to make experiments on the colouring of glass with iron, and that in
this art they acquired a dexterity not possessed at present, because it
was abandoned by our ancestors after the invention of smalt, which is
much more beautiful; and which can be used more easily and with more
certainty. I cannot, however, deny that I have often lamented this
loss when I saw the excellent blue in the painted windows at Gouda,
Goslar, and other places; though its beauty is much heightened by the
transparency of the glass, and the strong light that falls upon it from
without.
I shall now proceed to the invention of the colour prepared from
cobalt. About the end of the fifteenth century, cobalt appears to have
been dug up in great quantity in the mines on the borders of Saxony
and Bohemia, discovered not long before that period. As it was not
known at first to what purpose it could be applied, it was thrown
aside as a useless mineral. The miners had an aversion to it, not only
because it gave them much fruitless labour, but because it often proved
prejudicial to their health by the arsenical particles with which it
was combined; and it appears even that the mineralogical name _cobalt_
then first took its rise. At any rate, I have never met with it before
the beginning of the sixteenth century; and Mathesius and Agricola seem
to have first used it in their writings. Frisch derives it from the
Bohemian word _kow_, which signifies metal; but the conjecture that
it was formed from _cobalus_, which was the name of a spirit that,
according to the superstitious notions of the times, haunted mines,
destroyed the labours of the miners, and often gave them a great deal
of unnecessary trouble, is more probable; and there is reason to think
that the latter is borrowed from the Greek. The miners, perhaps, gave
this name to the mineral out of joke, because it thwarted them as much
as the supposed spirit, by exciting false hopes and rendering their
labour often fruitless[1487]. It was once customary, therefore, to
introduce into the church service a prayer that God would preserve
miners and their works from _kobolts_ and spirits.
Respecting the invention of making a useful kind of blue glass from
cobalt, we have no better information than that which Klotzsch[1488]
has published from the papers of Christian Lehmann. The former, author
of an historical work respecting the upper district of the mines in
Misnia, and a clergyman at Scheibenberg, collected with great diligence
every information in regard to the history of the neighbouring country,
and died, at a great age, in 1688. According to his account, the
colour-mills, at the time when he wrote, were about a hundred years
old; and as he began first to write towards the end of the thirty
years’ war, the invention seems to fall about 1540 or 1560. He relates
the circumstance as follows: “Christopher Schurer, a glass-maker at
Platten, a place which belongs still to Bohemia, retired to Neudeck,
where he established his business. Being once at Schneeberg, he
collected some of the beautiful coloured pieces of cobalt which were
found there, tried them in his furnace; and finding that they melted,
he mixed some cobalt with the vitreous mass, and obtained fine blue
glass. At first he prepared it only for the use of the potters; but
in the course of time it was carried as an article of merchandize
to Nuremberg, and thence to Holland. As painting on glass was then
much cultivated in the latter, the artists there knew better how to
appreciate this invention. Some Dutchmen therefore repaired to Neudeck,
in order that they might learn the process used in preparing this new
colour. By great promises they persuaded the inventor to remove to
Magdeburg, where he also made glass from the cobalt of Schneeberg;
but he again returned to his former residence, where he constructed
a hand-mill to grind his glass, and afterwards erected one driven by
water. At that period the colour was worth seven dollars and a half per
cwt., and in Holland from fifty to sixty florins. Eight colour-mills
of the same kind, for which roasted cobalt was procured in casks from
Schneeberg, were soon constructed in Holland; and it appears that the
Dutch must have been much better acquainted with the art of preparing,
and particularly with that of grinding it, than the Saxons; for the
elector John George sent for two colour-makers from Holland, and gave
a thousand florins towards enabling them to improve the art. He was
induced to make this advance chiefly by a remark of the people of
Schneeberg, that the part of the cobalt which dropped down while it
was roasting contained more colour than the roasted cobalt itself.
In a little time other colour-mills were erected around Schneeberg.
Hans Burghard, a merchant and chamberlain of Schneeberg, built one by
which the eleven mills at Platten were much injured. Paul Nordhoff, a
Frieslander, a man of great ingenuity, who lived at the Zwitter-mill,
made a great many experiments in order to improve the colour, by which
he was reduced to so much poverty that he was at length forced to
abandon that place, where he had been employed for ten years in the
colour-manufactory. He retired to Annaberg, established there in 1649,
by the assistance of a merchant at Leipsic, a colour-manufactory, of
which he was appointed the director; and by these means rendered the
Annaberg cobalt of utility. The consumption of this article however
must have decreased in the course of time; for in the year 1659,
when there were mills of the same kind at more of the towns in the
neighbourhood of mines, he had on hand above 8000 quintals.” Thus far
Lehmann.
This information is in some measure confirmed by Melzer[1489], who says
that the mines of Schneeberg, which were first discovered in the middle
of the fifteenth century, had declined so much towards the middle of
the sixteenth, that it was impossible to get any profit by them till
the year 1550, when a greater advantage arose from the new method
of using cobalt. About this period a contract was entered into with
the Dutch, who agreed to take the roasted cobalt at a certain price.
Lehmann[1490] says, but without adducing any proofs, that a manufactory
for making blue glass was erected by Sebastian Preussler, between
Platten and Eybenstock, so early as 1571. Rossler[1491], who died in
1673, in the seventy-sixth year of his age, gives us to understand that
a century and a half before his time, cobalt was procured and sold as
zaffer; but that the colour-mills in the country had been established
only about sixty years. I conjecture therefore that the roasted cobalt,
to which sand was added, in order that the nature of it might be better
concealed, and the further preparation of it rendered more difficult,
was given up to the Dutch, even so early as the beginning of the
sixteenth century[1492], and that these people by melting it anew, or
at any rate by pounding it finer, derived the greatest benefit from it
long before the Saxons themselves constructed mills according to the
model of those used in Holland. At present many Dutchmen grind German
cobalt with very great advantage[1493].
It appears that this new colour was not made known in books till a late
period. Agricola was not acquainted with the blue glass, nor is zaffera
mentioned either by him or Mathesius. Albin also, who indeed derived
the greater part of his information from these two writers, says not a
word respecting it; but he tells us that bismuth when put in vessels
grew together again[1494]. He seems therefore to allude to cobalt
roasted and mixed with sand, which when packed up becomes a solid body,
whereas bismuth which has been purified by roasting can never assume
that state. Vanuccio Biringoccio, the oldest writer in whose works I
have as yet observed the name _zaffera_, describes its use for painting
glass, and calls it a heavy mineral, without defining it any further.
Cardan[1495] gives the name of zaffera to an earth which colours glass
blue. Cæsalpin says it is a stone[1496]; and Julius Scaliger must
have known as little of it, else he would have mentioned it in his
Exercitations on Cardan. Porta, who employed great diligence to acquire
knowledge of this kind, often mentions _zaphara figlinorum_, without
telling us what it is; but he describes how it must be melted, poured
into water, pounded, sifted, and reduced into a fine powder in order
to be employed for making artificial precious stones[1497]. Neri, who
wrote about the year 1609[1498], knew nothing more of it; and Merret,
the commentator on Neri, who lived in the middle of the sixteenth
century[1499], confesses that he knew not what zaffera was, but he
believed that it was a new German invention, at least that it was
brought from Germany, and that it seemed to him to be made from copper
and sand, with the addition perhaps of calamine. The first person who
properly explained zaffera in his writings, and gave a correct account
of the method of preparing it, is, in my opinion, Kunkel[1500] in his
annotations on Neri and Merret. That writer says, zaffera was by the
miners called _zafloer_, and that sand was mixed with it only that the
powder-blue used by women for linen, and by painters called blue smalt,
might not be imitated in other countries.
Rosler says the Bohemian cobalt is not so good as that of Misnia, and
that its colour is more like that of ashes. That Brandt, a member of
the Council of Mines in Sweden, first asserted that cobalt contained a
peculiar kind of metal, must be so well known to mineralogists, that it
scarcely deserves to be mentioned[1501].