The ancients had certainly acquired great skill in the manufacture, as appears both from the accounts which have been preserved by ancient authors, and by the specimens which still exist—among which we may notice, as pre-eminently beautiful, that torment of antiquaries, the Portland vase, preserved in the British Museum. We have already adverted to another vase of the same kind, and of almost equal beauty, found in one of the tombs near the Gate of Herculaneum.
A remarkable story is told by Dion Cassius, of a man who, in the time of the Emperor Tiberius, brought a glass cup into the imperial presence and dashed it on the ground. To the wonder of the spectators, the vessel bent under the blow without breaking, and the ingenious artist immediately hammered out the bruise, and restored it whole and sound to its original form; in return for which display of his skill, Tiberius, it is said, ordered him to be immediately put to death.
The story is a strange one, yet it is confirmed by Pliny, who both mentions the discovery itself, and gives a clue to the motives which may have urged the emperor to a cruelty apparently so unprovoked. He speaks of an artificer who had invented a method of making flexible glass, and adds that Tiberius banished him, lest this new fashion should injure the workers in metal, of whose trade the manufacture of gold, silver, and other drinking-cups, and furniture for the table, formed an extensive and important branch.
The Romans were also well acquainted with the art of coloring glass, as appears, among other proofs, from the glass mosaics, of which mention has been made. Pliny speaks of a blood-red sort, called hæmatinum, from blood, of white glass, blue glass, etc. The most valuable sort, however, was the colorless crystal glass, for two cups of which, with handles on each side, Nero gave 6,000 sesterces, about $240.
Under this head we may speak of the vases called murrhina, since one theory respecting them is, that they were made of variegated glass. Their nature, however, is doubtful; not so their value. Pliny speaks of 70 talents being given for one holding three sextarii, about four and a half pints. Titus Petronius on his death-bed defrauded the avarice of Nero, who had compelled him, by a common piece of tyranny, to appoint the crown his heir by breaking a murrhine trulla, or flat bowl, worth 300 talents. Nero himself, as became a prince, outdid all by giving 100 talents for a single capis, or drinking-cup, "a memorable circumstance, that an emperor, and father of his country, should have drunk at so dear a rate." Pliny's description of this substance runs thus:
"It is to be noticed that we have these rich cassidoin vessels (called in Latin murrhina) from the East, and that from places otherwise not greatly renowned, but most within the kingdom of Parthia; howbeit the principal come from Carmania. The stone whereof these vessels are made is thought to be a certain humor, thickened as it were in the earth by heat. In no place are these stones found larger than small tablements of pillars or the like, and seldom were they so thick as to serve for such a drinking-cup as I have spoken of already. Resplendent are they in some sort, but it may rather be termed a gloss than a radiant and transparent clearness; but that which maketh them so much esteemed is the variety of colors, for in these stones a man shall perceive certain veins or spots, which, as they be turned about, resemble divers colors, inclining partly to purple and partly to white: he shall see them also of a third color composed of them both, resembling the flame of fire. Thus they pass from one to another as a man holdeth them, insomuch as their purple seemeth near akin to white, and their milky white to bear as much on the purple. Some esteem those cassidoin or murrhine stones, the richest, which present as it were certain reverberations of certain colors meeting altogether about their edges and extremities, such as we observe in rainbows; others are delighted with certain fatty spots appearing in them; and no account is made of them which show either pale or transparent in any part of them, for these be reckoned great faults and blemishes; in like manner if there be seen in the cassidoin any spots like corns of salts or warts, for then are they considered apt to split. Finally, the cassidoin stones are commended in some sort also for the smell that they do yield."
On these words of Pliny a great dispute has arisen. Some think that onyx is the material described, a conjecture founded on the variety of colors which that stone presents. To this it is objected, that onyx and murrha, onyx vases and murrhine vases are alike mentioned by Latin writers, and never with any hint as to their identity; nay, there is a passage in which Heliogabalus is said to have onyx and murrhine vases in constant use. Others, as we have said, think that they were variegated glass; others that they were the true Chinese porcelain, a conjecture in some degree strengthened by a line of Propertius:
"Murrheaq. in Parthis pocula cocta focis."
At the same time this quotation is not so conclusive as it might have been, since Pliny speaks of murrha as "hardened in the earth by heat," and the poet may only have meant the same thing, though the expression in that case would be somewhat strained. To us, Pliny's description appears to clearly point to some opaline substance; the precious opal has never in modern times been found in masses approaching to the size necessary to make vessels such as we have spoken of. The question is not likely to be settled, and it is not improbable that the material of these murrhine vases is entirely unknown to us, as the quarries of many marbles used by the ancients have hitherto eluded our research, and the marbles themselves are only known by their recurrence among ancient buildings.
We may here notice one or two facts connected with glass, which show that the ancients were on the verge of making one or two very important discoveries in physical science. They were acquainted with the power of transparent spherical bodies to produce heat by the transmission of light, though not with the manner in which that heat was generated by the concentration of the solar rays. Pliny mentions the fact that hollow glass balls filled with water would, when held opposite to the sun, grow hot enough to burn any cloth they touched; but the turn of his expression evidently leads to the conclusion that he believed the heat to become accumulated in the glass itself, not merely to be transmitted through it. Seneca speaks of similar glass balls, which magnified minute objects to the view. Nay, he had nearly stumbled on a more remarkable discovery, the composition of light, for he mentions the possibility of producing an artificial rainbow by the use of an angular glass rod. At a far earlier period Aristophanes speaks of "a transparent substance used to light fires with," usually translated glass. The passage is curious, as it shows a perfect acquaintance with the use of the burning glass.