It is highly probable that a limpid brook was the first mirror[136],
but we have reason to think that artificial mirrors were made as
mankind began to exercise their art and ingenuity on metals and
stones. Every solid body, capable of receiving a fine polish, would
be sufficient for this purpose; and indeed the oldest mirrors
mentioned in history were of metal. Those which occur in Job[137]
are praised on account of their hardness and solidity; and Moses
relates[138], that the brazen laver, or washing-basin, was made
from the mirrors of the women who had assembled at the door of the
tabernacle to present them, and which he caused them to deliver
up. As the women appeared in full dress at divine worship, it was
necessary for them to have looking-glasses after the Egyptian manner.
With these the washing-basins, according to the conjecture of most
interpretators, were only ornamented, covered, or perhaps hung round;
and Michaelis[139] himself was once of this opinion. But why should
we not rather believe that the mirrors were melted and formed into
washing-basins? As soon as mankind began to endeavour to make good
mirrors of metal, they must have remarked that every kind of metal was
not equally proper for that use, and that the best could be obtained
only from a mixture of different metals. In the mirrors however which
were collected by Moses, the artists had a sufficient stock of speculum
metal, and were not under the necessity of making it themselves; and
for this reason they could much more easily give to the whole basin
a polished surface, in which the priests, when they washed, might
survey themselves at full length. At any rate such a basin would not
be the only one employed instead of a mirror. Artemidorus[140] says
that he who dreams of viewing himself in a basin, will have a son
born to him by his maid. Dreams indeed are generally as groundless as
this interpretation; but one can hardly conjecture that Artemidorus
would have thought of such a dream, had it not been very common for
people to contemplate themselves in a basin. There were formerly a
kind of fortune-tellers, who pretended to show in polished basins to
the simple and ignorant, what they wished to know[141]. The ancients
also had drinking-vessels, the inside of which was cut into mirrors,
so disposed that the image of the person who drank from them was seen
multiplied[142]. Vopiscus mentions, among the valuable presents of
Valerian to the emperor Probus, when a tribune, a silver cup of great
weight, which was covered on the inside with mirrors of this sort[143].
Menard and others conjecture that mirrors in the time of Homer were
not much used, because he mentions them on no occasion, not even where
he describes in so circumstantial a manner the toilet of Juno[144]. In
answer to this, however, I have two things to observe. In the first
place, it is not to be expected that Homer should have mentioned every
article with which he was acquainted; and secondly, we are assured
by Callimachus, where he evidently has imitated the passage of Homer
before-quoted[145], that neither Juno nor Pallas employed a mirror when
they dressed. Mythology therefore did not allow the poet to introduce
a mirror upon the toilet of that deity. Polydore Vergilius, Boccace,
Menard, and others have all fallen into the error of making Æsculapius
the inventor of mirrors, though Cicero[146] seems to say the same
thing; but the best commentators have long since observed very justly,
that the Roman philosopher alludes not to a mirror but to a probe, the
invention of which we may allow to the father of medicine, who was at
first only a surgeon.
When one reflects upon the use made of metal mirrors, particularly
at Rome, to add to magnificence and for other purposes, and how
many artists, during many successive centuries, were employed in
constructing them, and vied to excel each other in their art, one
cannot help conjecturing that this branch of business must at those
periods have been carried to a high degree of perfection. It is
therefore to be regretted that they have not been particularly
described by any writer, and that on this account the art was
entirely lost after the invention of glass mirrors, which are much
more convenient. No one at that time entertained the least suspicion
that circumstances would afterwards occur which would render these
metal mirrors again necessary, as has been the case in our days by
the invention of the telescope. Our artists then were obliged to make
new experiments in order to discover the best mixture for mirrors of
metal; and this should be a warning to mankind, never to suffer arts
which have been once invented and useful to become again unknown. A
circumstantial description of them should at any rate be preserved for
the use of posterity, in libraries, the archives of human knowledge.
When we compare metals in regard to their fitness for mirrors, we shall
soon perceive that the hardest of a white colour possess in the highest
degree the necessary lustre. For this reason platina is preferable
to all others, as is proved from the experiments made by the Count
von Sickengen. Steel approaches nearest to this new metal, and silver
follows steel; but gold, copper, tin and lead, are much less endowed
with the requisite property. I have however observed among the ancients
no traces of steel mirrors; and it is probable they did not make any
of that metal, as it is so liable to become tarnished, or to contract
rust. An ancient steel-mirror is indeed said to have been once found,
but as some marks of silvering were perceived on it, a question arises
whether the silvered side was not properly the face of the mirror[147].
Besides, every person knows that a steel mirror would not retain its
lustre many centuries amidst ruins and rubbish.
The greater part of the ancient mirrors were made of silver, not on
account of costliness and magnificence, as many think, but because
silver, as has been said, was the fittest and the most durable of
all the then known unmixed metals for that use. In the Roman code of
laws, when silver plate is mentioned, under the heads of heirship
and succession by propinquity, silver mirrors are rarely omitted;
and Pliny[148], Seneca[149], and other writers, who inveigh against
luxury, tell us, ridiculing the extravagance of the age, that every
young woman in their time must have a silver mirror. These polished
silver plates may however have been very slight, for all the ancient
mirrors, preserved in collections, which I have ever seen, are only
covered with a thin coat of that expensive metal; and in the like
manner our artists have at length learned a method of making the cases
of gold and silver watches so thin and light, that every footman and
soldier can wear one. At first the finest silver only was employed for
these mirrors, because it was imagined that they could not be made of
that which was standard; but afterwards metal was used of an inferior
quality. Pliny tells us so expressly, and I form the same conclusion
from a passage of Plautus[150]. Philematium having taken up a mirror,
the prudent Scapha gives her a towel, and desires her to wipe her
fingers, lest her lover should suspect by the smell that she had been
receiving money. Fine silver however communicates as little smell to
the fingers as gold; but it is to be remembered that the ancients
understood much better than the moderns how to discover the fineness
of the noble metals by the smell, as many modes of proof which we use
to find out the alloy, were to them unknown. Money-changers therefore
employed their smell when they were desirous of trying the purity of
coin[151]. The witty thought of Vespasian, who, when reproached on
account of his tax upon urine, desired those who did so to smell the
money it produced, and to tell him whether it had any smell of the
article which was the object of it, alludes to this circumstance. In
the like manner many savage nations at present can by their smell
determine the purity of gold[152].
We are informed by Pliny, that Praxiteles, in the time of Pompey the
Great, made the first silver mirror, and that mirrors of that metal
were preferred to all others. Silver mirrors however were known
long before that period, as is proved by the passage of Plautus
above-quoted. To reconcile this contradiction, Meursius remarks that
Pliny speaks only of his countrymen, and not of the Greeks, who had
such articles much earlier, and the scene in Plautus is at Athens.
This therefore seems to justify the account of Pliny, but of what he
says afterwards I can find no explanation. Hardouin is of opinion,
that mirrors, according to the newest invention, at that period,
were covered behind with a plate of gold, as our mirrors are with an
amalgam. But as the ancient plates of silver were not transparent, how
could the gold at the back part of them produce any effect in regard to
the image? May not the meaning be, that a thin plate of gold was placed
at some distance before the mirror in order to throw more light upon
its surface? But whatever may have been the case, Pliny himself seems
not to have had much confidence in the invention.
Mirrors of copper, brass and gold, I have found mentioned only by the
poets, who perhaps employed the names of these metals because they
best suited their measure, or because they wished to use uncommon
expressions, and thought a golden mirror the noblest. By the brass ones
perhaps are to be understood only such as were made of mixed copper.
Did golden mirrors occur oftener, I should be inclined to refer the
epithet rather to the frame or ornaments than to the mirror itself; for
at present we say a gold watch, though the cases only may be of that
metal.
Mirrors seem for a long time to have been made of a mixture of copper
and tin, as is expressly said by Pliny[153], who adds, that the best
were constructed at Brundisium. This mixture, which was known to
Aristotle, produces a white metal, which, on account of its colour, may
have been extremely proper for the purpose, and even at present the
same mixture, according to the careful experiments made by Mr. Mudge,
an Englishman[154], produces the best metal for specula. It appears
that the ancients had not determined the proportion very accurately;
for Pliny assures us twice that in his time mirrors of silver were
preferred. It is indeed not easy to ascertain the quantity of each
metal that ought to be taken, and the most advantageous degree of heat;
upon which a great deal depends. One of the principal difficulties is
to cast the metal without blisters or air-holes, and without causing
any part of the tin to oxidize, which occasions knots and cracks, and
prevents it from receiving a fine polish. A passage of Lucian[155],
which no one as yet has been able to clear up, alludes certainly, in my
opinion, to these faults. A mixture of copper and tin is so brittle,
that it is very liable to crack; and a mirror formed of it, if not
preserved with great care, soon becomes so dim, that it cannot be used
till it has been previously cleaned and polished. For this reason a
sponge with pounded pumice-stone was generally suspended, from the
ancient mirrors, and they were kept likewise in a case or box, as may
be seen by the greater part of those still extant. Mirrors of silver
were less subject to this inconvenience, and I am inclined to think
that the latter on this account made the former be disused, as we are
informed by Pliny.
As ancient mirrors of metal are still to be found in collections of
antiquities, it might be of some importance to the arts if chemical
experiments were made on their composition. Those who have hitherto
given us any account of them have contented themselves with describing
their external figure and shape. Count Caylus[156] is the only person,
as far as I know, who caused any chemical experiments to be undertaken
on this subject. They were made on a mirror found near Naples, by M.
Roux, who asserts that the composition was a mixture of copper and
regulus of antimony, with a little lead. Antimony however was not known
to the ancients. If that metal was really a component part, the mirror
must have been the work of more modern times, or it must be allowed
that the artist had metal combined with antimony without knowing it;
but the latter is not probable. The experiments made by Roux do not
seem to me to have proved in a satisfactory manner the presence of
regulus of antimony; moreover, no certain information can be derived
from them, for the antiquity of the mirror was not ascertained; nor was
it known whether it ought to be reckoned amongst the best or the worst
of the period when it was made.
Those mirrors, which were so large that one could see one’s self
in them at full length, must, in all probability, have consisted
of polished plates of silver; for to cast plates of such a size of
copper and tin would have required more art than we can allow to those
periods; and I do not know whether our artists even now would succeed
in them[157].
We read in various authors, that, besides metals, the ancients formed
stones into mirrors, which were likewise in use. It is undoubtedly
certain that many stones, particularly of the vitreous kind, which are
opake and of a dark colour, would answer exceedingly well for that
purpose; but let the choice have been ever so good, they would not, in
this respect, have been nearly equal to metals. These of all mineral
bodies have the most perfect opacity; and for that reason the greatest
lustre: both these properties are produced by their solidity; and hence
they reflect more perfectly, and with more regularity, the rays of
light that proceed from other bodies. Our glass mirrors, indeed, are
properly metallic. Stones, on the other hand, have at any rate some,
though often hardly perceptible, transparency; so that many of the rays
of light are absorbed, or at least not reflected. Mention of stone
mirrors occurs also so seldom in the ancients, that we may conclude
they were made rather for ornament than real utility. In general, we
find accounts only of polished plates or panels of stone, fixed in the
walls of wainscoted apartments, which were celebrated on account of
their property of reflection.
Pliny[158] praises in this respect the obsidian stone, or, as it is
now called, the Icelandic agate. Everything that he says of it will be
perfectly intelligible to those who are acquainted with this species of
stone or vitrified lava. The image reflected from a box made of it,
which I have in my possession, is like a shadow or silhouette; but with
this difference, that one sees not only the contour, but also the whole
figure distinctly, though the colours are darkened. To form it into
images and utensils, which Pliny speaks of, must have been exceedingly
difficult, on account of its brittleness. I saw at Copenhagen, among
other things made of it, a drinking-cup and cover, on which the artist
had been employed four years.
Domitian, when he suspected that plots were formed against him, caused
a gallery, in which he used to walk, to be lined with _phengites_,
which by its reflection showed everything that was done behind his
back[159]. Under that appellation we are undoubtedly to understand
a calcareous or gypseous spar, or selenite, which is indeed capable
of reflecting an image; but we cannot therefore pretend to say that
the ancients formed mirrors of it; nor do I explain what Pliny says,
where he speaks of the _phengites_, as if whole buildings had been
once constructed of it[160]. That kind of stone, for various reasons,
and particularly on account of its brittleness, is altogether unfit
for such a purpose. At those periods, the windows of houses were open,
and not filled up with any transparent substance, but only covered,
sometimes by lattices or curtains. It is probable, therefore, that
those openings of the walls of the building mentioned by Pliny, where
the windows used to be, were filled up with _phengites_, which, by
admitting a faint light, prevented the place from being dark even when
the doors were shut; so that Pliny might say, “It appeared as if the
light did not fall into the building, but as if it were inclosed in it.”
I might be accused of omission did I not here mention also a passage
of Pliny[161], where he seems to speak of a mirror made of an
emerald, which Nero used to assist him to see the combats of the
gladiators. Cary asserts that Nero was short-sighted, and that his
emerald was formed like a concave lens. The former is expressly
said by Pliny[162], but the latter, though by Abat considered not
improbable[163], I can scarcely allow myself to believe, because such
an interpretation of Pliny’s words is too forced, and because they
can be explained much better in another manner. As no mention of such
an excellent help to short-sighted people is to be found in any other
ancient author, we must allow, if Cary’s opinion be adopted, that
this property of the concave emerald was casually remarked, and that
no experiments were made to cut any other natural or artificial glass
in the same form for the like use, because people imagined that this
property was peculiar to the emerald alone, which was then commonly
supposed to be endowed with the power of greatly strengthening the
eye-sight. Much more probable to me is the explanation of an Italian,
which Abat also does not entirely reject, that the emerald had a smooth
polished surface, and served Nero as a mirror[164]; and the passage of
Pliny alluded to seems to have been thus understood by Isidore[165]
and Marbodæus. It may here be objected, that real emeralds are too
small to admit of being used as mirrors; but the ancients speak of some
sufficiently large for that purpose, and also of artificial ones[166];
so that we may with certainty conclude, that they classed among the
emeralds fluor-spar green vitrified lava, or the green Icelandic
agate as it is called, green jasper, and also green glass. The piece
of green glass in the monastery of Reichenau, which is seven inches
in length, three inches in thickness, and weighs twenty-eight pounds
three-quarters; and the large cup at Genoa, which is however full of
flaws[167], have been given out to be emeralds even to the present time.
Mirrors were made also of rubies, as we are assured by Pliny[168], who
refers to Theophrastus for his authority; but this precious stone is
never found now of such a size as to render this use possible; and Gary
and the anonymous Italian before-mentioned have proved very properly
that Pliny has committed a gross mistake, which has not been observed
by Hardouin. Theophrastus, in the passage alluded to[169], does not
speak of a ruby, but of the well-known black marble of Chio, though he
calls both _carbunculus_, a name given to the ruby on account of its
likeness to a burning coal, and to the black marble on account of its
likeness to a quenched coal or cinder; and the latter, as well as the
obsidian stone, was used sometimes for mirrors.
The account how mirrors were formed by the native Americans, before
they had the misfortune to become acquainted with the Europeans, is
of considerable importance in the history of this art. These people
had indeed mirrors which the Europeans could not help admiring. Some
of them were made of black, somewhat transparent, vitrified lava,
called by the Spaniards _gallinazo_, and which is of the same kind as
the obsidian stone employed by the Romans for the like purpose. Of
this substance the Americans had plane, concave, and convex mirrors.
They had others also made of a mineral called the Inca’s stone[170],
which, as has been already said by Bomare, Sage, Wallerius, and other
mineralogists, was a compact pyrites or marcasite, susceptible of a
fine polish; and on that account often brought to Europe, and worn
formerly in rings under the name of the stone of health. Ulloa says the
Inca’s stone is brittle, opake, and of a somewhat bluish colour; it
has often veins which cannot be polished, and where these veins are it
frequently breaks. The mirrors formed of it, which he saw, were from
two to three inches in diameter; but he saw one which was a foot and a
half. The opinion which some have entertained, that these mirrors were
cast, has no other foundation than the likeness of polished marcasite
to cast brass. This mineral is very proper for reflecting images; and
I am inclined to think that the Peruvians had better mirrors than the
Greeks or the Romans, among whom we find no traces of marcasite being
employed in that manner. It appears, however, that the Indians had
mirrors also of silver, copper, and brass[171].
I come now to the question in what century were invented our glass
mirrors, which consist of a glass plate covered at the back with
a thin leaf of metal. This question has been answered by some with
so much confidence, that one might almost consider the point to be
determined; but instead of real proofs, we find only conjectures or
probabilities; and I must here remark, that I cannot help thinking
that they are older than has hitherto been supposed, however desirous
I may be to separate historical truth from conjecture. When I have
brought together everything which I know on the subject, I would say,
that attempts were even made at Sidon to form mirrors of glass; but
that they must have been inferior to those of metal, because they did
not banish the use of the latter. The first glass mirrors appear to me
to have been of black-coloured glass, or an imitation of the obsidian
stone; and to have been formed afterwards of a glass plate with some
black foil placed behind it[172]. At a much later period, blown glass,
while hot, was covered in the inside with lead or some metallic
mixture; and still later, and, as appears, first at Murano, artists
began to cover plates of glass with an amalgam of tin and quicksilver.
The newest improvements are, the casting of glass-plates, and the art
of making plates equally large by blowing and stretching, without the
expensive and uncertain process which is required for casting.
That glass mirrors were made at the celebrated glass-houses of Sidon,
is mentioned so clearly by Pliny that it cannot be doubted[173].
When I read the passage, however, without prejudice, without taking
into consideration what others have said on it, and compare it with
what certain information the ancients, in my opinion, give on the
same subject, I can understand it no otherwise than as if the author
said, that the art of manufacturing glass various ways was invented,
principally, at Sidon, where attempts had been made to form mirrors
of it. He appears therefore to allude to experiments which had not
completely succeeded; and to say that such attempts, at the time when
he wrote, had been entirely abandoned and were almost forgotten.
Had this circumstance formed an epoch in the art, Pliny, in another
place, where he describes the various improvements of it so fully,
would not have omitted it; but of those experiments he makes no
further mention[174]. All the inventions which he speaks of, evidently
relate to metal mirrors only, of which the silver, at that time,
were the newest. Had the Sidonian mirrors consisted of glass plates
covered at the back, those of metal, the making of which was, at any
rate, attended with no less trouble, which were more inconvenient
for use on account of their aptness to break, their requiring to
be frequently cleaned and preserved in a case, and which were more
unpleasant on account of the faint, dull image which they reflected,
could not possibly have continued so long in use as they really did;
and circumstances and expressions relative to glass mirrors must
certainly have occurred. Though glass continued long to be held in high
estimation, particularly at Rome; and though many kinds of glass-ware
are mentioned in ancient authors, among costly pieces of furniture,
mirrors are mentioned only among articles of silver plate. I am
acquainted with no certain trace of glass mirrors from the time of
Pliny to the thirteenth century; but after that period, at which they
are spoken of in the clearest manner, we find them often mentioned in
every century; and mirrors of metal at length entirely disappear.
How the Sidonian mirrors were made, is not known; but if I may
be allowed a conjecture, I am of opinion that they consisted of
dark-coloured glass, which had a resemblance to the obsidian stone.
Such is the usual progress of inventions. At those periods one had no
other representation of glass mirrors than that afforded by natural
glass or vitreous stones. When artists wished to make mirrors of
glass, they would try to imitate the latter. After the invention
of printing, people endeavoured to render printed books as like as
possible to manuscripts; because they imagined that this invention
was to be approved only so far as it enabled them to imitate these,
without observing that it could far excel the art of writing. But the
Sidonian glass mirrors were so much surpassed by the silver or brass
ones, which perhaps were invented about the same time, that on this
account they were never brought into use. Glass mirrors, perhaps, would
have been invented sooner, had mankind employed at an earlier period
glass-windows, which often, when they are shut on the outside so
that no light can pass through them, reflect images in a much better
manner than the best mirrors of metal. This observation, which may be
made daily, would then, in all probability, have been sooner turned to
advantage.
No one has employed a greater profusion of words to maintain an opinion
opposite to mine, than Abat; but when his proofs are divested of their
ornaments, they appear so weak that one has very little inclination
to agree with him. “The observation,” says he, “that a plate of
glass is the best mirror, when all other rays of light, except those
reflected back from the glass, are prevented, by a metallic covering
placed behind it, from falling on the eye, is so easy, that it must
have been made immediately after the invention of glass.” Who does
not think here of Columbus and his egg? Instances occur in history of
many having approached so near an invention, that we are astonished
how they could have missed it; so that we may exclaim with a certain
emperor, “Taurum toties non ferire difficile est[175].” “The Sidonian
invention,” continues he, “would not have been worth mentioning, had it
not produced better mirrors than those which the ancients had before
of the obsidian stone. But these even are mentioned only once, in so
short and abrupt a manner, and as it were out of ridicule, that one may
easily perceive they were not much esteemed.” “If the Sidonians,” adds
he, “were not the inventors, let some other inventor be mentioned;”
and he assures us that he had sought information on this subject, in
Neri, Kunkel, and Merret, but without success. That I believe; but Abat
does not remark that by the same manner of reasoning we may ascribe to
the Sidonians the invention of watches, and many other articles, the
inventors of which are not to be found in books where they ought as
much to be expected as the inventor of glass in Neri. The grounds on
which many old commentators of the Bible, Nicholas de Lyra and others,
have supposed that glass mirrors were known so early as the time of
Moses, are still weaker. If quoting the names of writers who entertain
a like opinion be of any weight, I could produce a much greater number
of learned men, who, after an express examination of the question, deny
altogether that glass mirrors were used by the ancients.
Dr. Watson[176] also has endeavoured to support the opinion of Abat,
but with less confidence and with more critical acumen. His grounds,
I think, I have weakened already; but one observation here deserves
not to be overlooked, because it suggests an idea that may serve to
illustrate a passage of Pliny, which, as I before remarked, has never
yet been explained. “If we admit,” says he, “that Pliny was acquainted
with glass mirrors, we may thus understand what he says respecting
an invention, which was then new, of applying gold behind a mirror.”
Instead of an amalgam of tin, some one had proposed to cover the back
of the mirror with an amalgam of gold, with which the ancients were
certainly acquainted, and which they employed in gilding[177]. He
mentions, also, on this occasion, that a thought had once occurred to
Buffon, that an amalgam of gold might be much better for mirrors than
that used at present[178]. This conjecture appears, at any rate, to be
ingenious; but when I read the passage again, without prejudice, I can
hardly believe that Pliny alludes to a plate of glass in a place where
he speaks only of metallic mirrors; and the overlaying with amalgam
requires too much art to allow me to ascribe it to such a period
without sufficient proof. I consider it more probable that some person
had tried, by means of a polished plate of gold, to collect the rays of
light, and to throw them either on the mirror or the object, in order
to render the image brighter.
Professor Heeren showed me a passage in the Ecloga of Stobæus, which,
on the first view, seems to allude to a glass mirror[179]. It is
there said, Philolaus the Pythagorean believed that the sun was a
vitreous body, which only received the rays of the æthereal fire and
reflected them to us like a mirror. When we compare, however, the words
of Stobæus with those by which Plutarch[180], Achilles Tatius[181],
Eusebius[182], and others, express the same thing, that meaning
cannot be drawn from them. It appears, at first, as if Philolaus had
considered the sun to be transparent, and supposed that the rays
passed through it, and came condensed to our earth, in the same manner
as they are brought to a focus by a glass globe. Some commentators have
explained the passage in this manner; and on account of the affinity of
the Greek words have thought also of a funnel. In that case, however,
the comparison of the sun with a mirror would not have been just; and
if it be admitted that Philolaus considered the sun as a bright body
endowed with the property of reflection, what he says of rays passing
or transmitted through it, and of the pores of the sun’s body, will
become unintelligible. But even if we adopt the last explanation, that
Philolaus imagined the sun to be a mirror, it does not follow that he
had any idea of a glass one[183]; and besides, he only speaks of a body
capable of reflecting a strong light; and that glass, under certain
circumstances, is fit for that purpose, may have been remarked as soon
as it was invented, though men might not find out the art of forming
it into proper mirrors by placing some opake substance behind it[184].
Empedocles also said, that the sun was a mirror, and that the light
received by our earth was the reflection of the æthereal fire, which
Eusebius compares to the reflection made by water[185].
In the problems ascribed to Alexander of Aphrodisias, glass mirrors,
covered on the back with tin, are clearly mentioned; but this
information does not lead us one step further in the history of the
art; as it is proved that the above Alexander, who lived in the
beginning of the third century, could not have written that work. The
author, who must have been a physician, maintains the immortality of
the soul, which Alexander of Aphrodisias, with Aristotle, denies. Some
therefore have ascribed these problems to Alexander Trallianus, who
practised physic in the middle of the sixth century; but this is only
a conjecture which no one has as yet rendered probable, especially as
there have been many physicians of the name of Alexander. The problem
to which I allude is not to be found in every manuscript and edition;
so that it is doubtful whether it may not be the production of a later
author than that of the rest of the book, particularly as it is certain
that many who had it in their possession added problems of various
kinds according to their pleasure. However this may be, it is evident
that the author of this problem was acquainted with mirrors covered at
the back; and the expression which he uses does not merely imply that
a leaf of tin was placed behind the glass plate, but that the tin in
a liquid state was rubbed over it. The old French translator thinks
that the author speaks of windows; but that opinion is undoubtedly
false[186].
Of as little importance as the above passage of Alexander, is another
of Isidore, often quoted in support of the antiquity of glass mirrors.
On the first view it appears to be a testimony of great weight; but
when closely examined it becomes reduced to very little. “Nothing,”
says he, “is so fit for mirrors as glass[187].” Abat and others, who
have considered these words as decisive, make less hesitation to
ascribe to the sixth century, in which Isidore lived, a knowledge
of mirrors covered on the back with tin and quicksilver, as the same
writer, in another place, observes, that quicksilver can be kept in no
vessel but one of glass[188]. It is very true that a glass filled with
that metal will form a very good mirror; but I am of opinion that this
may have been long known, before people thought of making an amalgam of
tin and quicksilver in order to cover the backs of mirrors. The first
passage, which is properly the one of any consequence, loses its force
when we see that it is taken from Pliny and copied incorrectly. The
latter says, that one can give to glass every kind of shape and colour,
and that no substance is more ductile, or fitter to be moulded into any
form[189]. Isidore, as is usual, says the same thing, and in the same
words, except, that instead of _sequacior_ he substitutes _speculis
aptior_; so that the mention of a mirror is altogether unexpected, and
so little suited to what goes before and what follows, that one must
believe that this alteration, occasioned perhaps by the similitude of
the words, or by an abbreviation, was not made by Isidore, but by some
transcriber. But even if we believe that Isidore himself spoke of glass
being used at that period for mirrors, we are not able to comprehend,
from what he says, how glass mirrors were made in the sixth century.
I have met with no information respecting this subject in the whole
period between the age of Isidore and the eleventh century. About the
year 1100, at least as is supposed not without probability, Alhazen the
Arabian wrote his well-known treatise on Optics, in which I conjectured
that I should find mention made of glass mirrors; but I searched that
work in vain, though I must confess I did not read it through entirely.
Where he begins his catoptrical lessons, he however often speaks of
iron mirrors, by which we may understand mirrors of the best steel. In
explaining a certain phænomenon, he says, that the cause of it cannot
be in the darkness of the iron mirror, because if a mirror of silver be
used, the same effects will be produced. Would he not on this occasion
have introduced glass mirrors, had he been as well-acquainted with them
as with those already mentioned? At first, he never speaks of mirrors
without adding of iron, of silver; but he mentions them afterwards
without any epithet of the kind.
All these mirrors I find also in the Optics of Vitello, who wrote
in the middle of the thirteenth century, in Italy, a country which
was at that time almost the only one where the arts flourished[190].
That author has, indeed, borrowed a great deal from Alhazen, though
there are many things of his own, and he gives an account of some
experiments on the refracting power of glass; but he never, as far as
I have observed, mentions glass mirrors. Whether Jordanus Nemorarius,
or Nemoratius, who also wrote, in the thirteenth century, a book _De
Speculorum Natura_, makes mention of them, I do not know, because I
have never had an opportunity of seeing that work. I am of opinion it
was never printed.
It is in the thirteenth century, that I find the first undoubted
mention of glass mirrors covered at the back with tin or lead. Johannes
Peckham, or Peccam, an English Franciscan monk, who taught at Oxford,
Paris, and Rome, and who died in 1292, wrote about the year 1279 a
treatise of optics, which was once printed, with the title of Johannis
Pisani Perspectiva Communis[191]. In this work, besides mirrors made of
iron, steel, and polished marble, the author not only speaks often of
glass mirrors, but says also that they were covered on the back with
lead, and that no image was reflected when the lead was scraped off.
Vincentius Bellovacensis[192] speaks in a manner still clearer, for
he tells us that lead was poured over the glass plate while hot. To
the same century also belong the concurrent testimonies of Raimundus
Lullius[193], Roger Bacon[194], Antonius di Padua[195], and Nicephorus
Gregoras[196], who died after the year 1360[197].
That this invention cannot be much older we have reason to conclude,
because glass mirrors were extremely scarce in France even in the
fourteenth century, while mirrors of metal were in common use; and
we are told that the mirror of Anne de Bretagne, consort of Louis
XII., was of the latter kind[198]. Metal mirrors also were made and
employed in Persia and the East, where indeed ancient usages continued
longest, and glass mirrors were not known there till the commencement
of the European trade with these remote regions. The former are still
preferred in those countries, because they are not so liable to break,
and can be preserved better in a dry hot climate than the amalgam of
the latter.
Respecting the progress of this art, I know nothing more than what
follows:--At first, melted lead, or perhaps tin, was poured over the
glass plate while yet hot as it came from the furnace. This process
agrees with that which, since very early periods, has been employed
in or around Nuremberg for making convex mirrors by blowing with the
pipe into the glass-bubble whilst still hot a metallic mixture, with a
little resin or salt of tartar, which prevents oxidation and assists
the fusion. When the bubble is covered all over in the inside, and
after it has cooled, it is cut into small round mirrors. This art is
an old German invention, for it is described by Porta and Garzoni, who
both lived in the beginning of the sixteenth century, and who both
expressly say, that it was then common in Germany. Curious foreigners
often attempted to learn it, and imagined that the Germans kept it
a secret. Boyle made various experiments in order to discover the
process; and the secretary of the Royal Society endeavoured, by means
of the ambassador from Charles II., who, perhaps about 1670, resided
at Frankfort, to obtain a knowledge of it; but did not succeed, as we
are told by Leibnitz[199]. It was called the art of preparing mirrors
without foil; and it was highly esteemed, because it was supposed that
it might be useful to those fond of catoptrics, by enabling them to
form convex and concave mirrors themselves. This account of Leibnitz
seems to have led Von Murr into a slight error, and induced him to
believe that the art of making convex mirrors without foil was first
found out at Nuremberg in 1670. I introduce this remark because I
flatter myself he will not be displeased that I make the above service,
rendered by his native city, to be a century and a half older. These
small convex mirrors, which reflect a diminished, but a clearer image
than our usual mirrors, are perhaps made still, though they are not
now carried round so frequently for sale in Germany as they were
thirty years ago, at which time, if I remember right, they were called
(_Ochsen-augen_) ox-eyes. They were set in a round painted board, and
had a very broad border or margin. One of them, in my possession,
is two inches and a half in diameter. It is probable that the low
price of plane mirrors, when glass-houses began to be more numerous,
occasioned these convex ones to be little sought after. The mixture
employed in making them was, according to Porta, antimony, lead, and
colophonium; but according to Garzoni, it was _una mistura di piombo,
stagno, marchesita d’argento, e tartaro_, which in the German edition
is translated very badly, “lead, tin, flint, silver, and tartar.” The
following observation perhaps is not altogether useless: Colophonium,
which is employed on many other occasions for soldering, was formerly
called mirror-resin, and was sold under that name even in the beginning
of the present century. Frisch assigns no reason for this appellation,
and Jacobson gives a wrong one, viz. its having a bright shining
surface when broken. The true reason was the above-mentioned use; and
as that is now very little known, it is called from that to which it is
principally applied, violin-resin.
It appears that, instead of pouring melted metal over plates of glass,
artists for some time applied to them the before-mentioned amalgam
of tin, or covered them in some other manner, perhaps in the same way
as Boyle covered concave glasses in the inside. Porta however saw
almost the same process employed at Murano as that which is still
followed at present. The tin, hammered to thin leaves, was spread
out very smoothly; and quicksilver was poured over it, and rubbed
into it, either with the hand or a hare’s foot; and when the tin was
saturated it was covered with paper. The glass, wiped exceedingly
clean, was then laid above it; and while the workman pressed it down
with his left hand, he drew out very carefully with his right the
paper that lay between the tin and the glass, over which weights were
afterwards placed. This much at any rate is certain, that the method of
covering with tin foil was known at Murano so early as the sixteenth
century[200], and therefore it is much older than J. M. Hoffmann
supposes. To conclude, whether this ingenious invention belongs to the
Venetians, as several later, and particularly Italian, writers assert,
I can neither prove nor contradict; but it is well known that till
about the end of the seventeenth century their mirrors were sold all
over Europe and in both the Indies. After that period the glass-houses
in other countries were improved, and new ones established; and the
discovery made in France, that glass, like metal, could be cast into
much larger plates than had been before prepared by blowing and
rolling, was in more than one respect prejudicial to the sale of those
made at Venice.
So early as the year 1634, attempts were made in France to establish
glass-houses for manufacturing mirrors, and Eustache Grandmont obtained
a patent for that purpose; but his undertaking was not attended with
success. As Colbert exerted himself very much to promote manufactures
of every kind, Nicholas de Noyer proposed to make mirrors according to
the Venetian method. This plan was adopted by Charles Rivière, sieur
du Freni, valet-de-chambre to the king; and having procured the royal
permission, he sold it afterwards for a large sum to De Noyer, who,
in 1665, received a confirmation of the patent, and an advance of
12,000 livres for four years, on condition of his procuring workmen
from Venice, who, after serving eight years in the kingdom, were to
be naturalized. De Noyer was joined by several more, who entered
into partnership with him, and particularly by one Poquelin, who had
hitherto carried on the greatest trade in Venetian mirrors, and who
engaged workmen from Murano. The glass-houses were erected at the
village of Tourlaville, near Cherbourg, in Lower Normandy. After the
death of Colbert, who was succeeded by Louvois, the charter of the
company was in 1684 renewed for thirty years longer, and at that period
Pierre de Bagneux was at the head of it.
Scarcely had five years of this period elapsed, when, in 1688, Abraham
Thevart made a proposal to the court for casting glass mirrors of
a much larger size than any ever before made. This plan, after an
accurate investigation, was approved; and in the same year he received
the royal permission to use his invention for thirty years, but it was
not registered till 1693 or 1694. The first plates were cast at Paris,
and astonished every artist who saw them. They were eighty-four inches
in height, and fifty in breadth. In order to lessen the excessive
expense, the glass-houses were erected at St. Gobin, in Picardy; and
to prevent all dispute with the old privileged company, Thevart was
expressly bound to make plates at least sixty inches in length and
forty in breadth, whereas the largest of those made before had never
exceeded forty-five or fifty inches in length. On the other hand, the
old company were allowed to make plates of a smaller size, and were
prohibited from employing any of the instruments or apparatus invented
by Thevart. These however had not been so accurately defined as to
remove all cause of litigation between the companies, and for that
reason permission was at length granted, in 1695, for both to be united
into one, under the inspection of François Plastrier, to whom the king,
in 1699, sold the palace of St. Gobin. After this they declined so
rapidly, that in 1701 they were not able to pay their debts, and were
obliged to abandon several of the furnaces. To add to their misfortune,
some of the workmen whom they had discharged retired to other
countries, which were already jealous of the French invention, and
wished to turn it to their advantage. The French writers assert that
their attempts never succeeded, and that most of the workmen returned
again to France, when a new company was formed in 1702, under the
management of Antoine d’Agincourt, who by prudent œconomy improved the
establishment, so as to render the profit very considerable. At present
mirrors are cast as well as blown, both at St. Gobin and at Cherbourg;
and in 1758 the price of them was greatly reduced, in order probably to
weaken the competition of the foreign glass-houses, among which there
are many not inferior to the French.
This short history of the glass manufactories in France is collected
from Savary[201] and Expilly[202]. A more particular account perhaps
may be expected of the inventor, of his first experiments, and of their
success; but notwithstanding a strict search, I have not been able to
find any further information on the subject. We are told only that his
name was sieur Abraham Thevart, though the historians who record that
circumstance have filled their pages with uninteresting anecdotes, and
even with the vices of many of the courtiers of the same period.
The principal benefit which has arisen to the art from this invention,
properly is, that much larger mirrors can be obtained than formerly;
for when attempts were made to blow very large plates, they were always
too thin. Casting, however, besides great expense in apparatus[203],
requires so many expert workmen, and so tedious and severe labour, and
is accompanied with so much danger, that it is only seldom that plates
of an extraordinary size succeed, and the greater part of them must be
cut into smaller plates which might have been blown. Those cast are
never so even and smooth as those that have been blown; they require
therefore a great deal of polishing, and on that account must be very
thick. The monstrous mass requisite for a mirror of the largest size,
stands ready melted in a very frail red-hot earthen pot, which is taken
from the furnace and placed upon an iron plate, strongly heated, that
the mass may be cast upon it into a glass plate. The latter must then
be speedily conveyed to the cooling-furnace, and if it be found free
from faults, it is ground, polished and silvered; but the last part
of the process is generally done at the place where a purchaser can
be found for so expensive an article, in order that less loss may be
sustained in case it should happen to break by the way.
These great difficulties, which have excited the astonishment of every
one who has seen the process, and that of finding sale for so expensive
and magnificent wares, have obliged artists to return to the old method
of blowing; and many have been so fortunate in improving this branch of
manufacture, that plates are formed now by blowing, sixty-four Flemish
inches in height and twenty-three in breadth, which it was impossible
to make before but by casting.
The mass of matter necessary for this purpose, weighing more than a
hundred pounds, is by the workman blown into the shape of a large bag;
it is then reduced to the form of a cylinder, and being cut up, is, by
stretching, rolling it with a smooth iron, and other means, transformed
into an even plane.
[All but the very commonest mirrors are now made of plate-glass; which
is also used to a great extent for window-panes, and is manufactured
by casting, rolling and polishing. The enormous plates of glass which
are seen in many of the large shops of this city are well-calculated
to excite the astonishment of those who are not yet aware of the
late improvements in this branch of manufacture. An idea of what may
be accomplished by blowing was given in 1845, at the Exhibition at
Vienna, where a blown glass 7 feet in length and 3½ in breadth was
exhibited; and which was of sufficient thickness to admit of polishing.
Nevertheless, the casting of plate-glass is now managed with such
comparative ease, that there appears to be no limit to the size to
which the plates can be brought, so that the blowing of large panes
of glass is given up in this country. Private houses may now be seen
decorated with single sheets of glass upwards of 20 feet in height and
10 in width.
A patent for a very ingenious process for silvering glass was taken
out in November 1843 by Mr. Drayton. It consists in depositing silver,
from a solution, upon glass, by deoxidizing the oxide of silver in
solution, so that the precipitate will adhere to the glass, without the
latter having been coated with metallic or other substances. This is
effected by mixing 1 oz. of coarsely powdered nitrate of silver with
½ oz. of spirits of hartshorn and 2 oz. of water; after standing for
24 hours, the mixture is filtered (the deposit on the filter, which
contains silver, being preserved), and an addition is made thereto of
3 oz. of spirit (by preference, spirit of wine) at 60° above proof, or
naphtha; from 20 to 30 drops of oil of cassia are then added, and after
remaining for about 6 hours longer, the solution is ready for use. The
glass to be silvered must have a clean and polished surface; it is to
be placed in a horizontal position, and a wall of putty formed around
it, so that the solution may cover the surface of the glass to the
depth of from ⅛th to ¼th of an inch. After the solution has been
poured on the glass, from 6 to 12 drops of a mixture of oil of cloves
and spirit of wine (in the proportion of 1 part by measure of the oil
to 3 of spirit of wine) are dropped into it at different places; or
the diluted oil of cloves may be mixed with the solution before it is
poured upon the glass; the more oil of cloves used, the more rapid
will be the deposition of the silver, but the patentee prefers that
it should occupy about two hours. When the required deposit has been
obtained, the solution is poured off; and as soon as the silver on the
glass is perfectly dry, it is varnished with a composition, formed by
melting together equal quantities of bees’ wax and tallow. The patentee
states that, by experiment, he has ascertained that about 18 grs. of
nitrate of silver are used for each square foot of glass.
It has been urged as an objection to this process, that in the course
of a few weeks the surfaces of the mirrors formed by it become dotted
over with small brownish-red spots, which greatly injures their
appearance. Dr. Stenhouse states that these spots are caused by the
metallic silver, whilst being deposited on the surface of the glass,
carrying down with it mechanically small quantities of a resinous
matter, resulting most probably from the oxidation of the oil. This
subsequently acts upon the metallic surface with which it is in
contact, and produces the small brown spots already mentioned. Mr.
Drayton, however, states that the brown spots only occur when the oil
employed is old and unfit for use.]