As far as contemporary evidence goes, all our information on the first head is derived from the brief and very unsatisfactory statements of Pliny. There is, however, every reason to believe that there were few important changes in the construction of the furnaces, or in the preparation of the materials, during the time that intervened between, say, the fourth century of our era and the period in the Middle Ages with regard to which we have further sources of information. That is to say, we may regard the comparatively adequate account of the manufacture of glass given by the monk Theophilus, and by the pseudo-Heraclius,[[44]] as on the whole applicable to Roman times. Even at the present day at Murano, and doubtless at other glass-works little affected by modern industrial processes, much of the old method of working and many of the old terms remain almost unchanged. To give but one example:—when the workman is preparing the half-liquid gathering or ball of glass at the end of his blowing-tube, previous to inflating it with his breath to form the paraison or vesicle, he trundles the viscous mass upon a slab of iron which rests on the ground beside his furnace. This iron slab is known as the ‘marver’—there are similar names for it in other European languages—and it is always understood that the plate in question was formerly made of marble. So, no doubt, it may have been at some remote period, but we find that the pseudo-Heraclius, describing in the twelfth century or thereabouts the manufacture of glass, speaks of this same plate as ‘tabula ferri quæ marmor vocatur.’ Perhaps we should have to go back to the stone slab on which the Egyptian glass was rolled to find the origin of this ‘marver.’[[45]]
We must now see what can be made out of the somewhat rambling account of the origin and manufacture of glass given by Pliny at the end of his thirty-sixth book (cap. 44-47). Pliny regarded glass as a Syrian invention. For many centuries, he tells us, the sole source of the principal constituent was a small tract of sand thrown up by the sea at a spot on the Phœnician coast near the town of Ptolemais, where the river Belus[[46]] flows into the Mediterranean. With this sand the natives mixed the nitrum, imported oversea in cakes,[[47]] and thereby for the first time formed glass. According to Pliny, these Phœnicians were astute and ingenious craftsmen, and they, in time, took to adding to their glass-pots the ‘magnes lapis, which, it is asserted, draws to it the melted glass like iron.’ This is a statement most characteristic of Pliny. The magnes lapis—magnetic iron-ore or loadstone—is the last substance in the world any one would think of adding to glass. But we know that the ancients knew of two kinds of black stone, for one of which they used the masculine form magnes—this was the loadstone—for the other the female form magnesia;[[48]] and this magnesia, at any rate at a somewhat later period, can be undoubtedly identified with the black oxide of manganese (MnO2), a substance known of old as the ‘soap of glass,’ from its power of removing the green colour derived from iron. Now we have seen that pure white glass, ‘cleansed’ probably by this method, had only comparatively lately been introduced into Italy, and some confused account of the new discovery had probably reached Pliny’s ears. ‘In the same way,’ he continues, ‘they took to adding to the fused mass shining pebbles, then shells and sandy concretions (fossiles arenæ).’ In these ‘fossils’ we may, perhaps, recognise the source from which was obtained the lime, an essential constituent of glass. Passing over some obscure references to the nitre of Ophir and the copper of Cyprus, Pliny goes on to say that the whole is melted ‘like bronze,’ in closely grouped furnaces, and that a blackish mass of fatty aspect is obtained. This we must regard as a preliminary frit, for we are told that the mass is melted again in the glass-house, where the requisite colouring matter is added to it. ‘So the work was carried on of old in the famous glass-works of Sidon.... At times the glass was shaped by blowing, or again it was abraded by the wheel, or carved in the manner of silver.... Such was the ancient way of making glass. At the present day in Italy also, by the mouth of the river Vulturnus, for a space of six miles between Cumæ and Liternum, a white and most soft sand is collected, which is pounded both in mortar and mill; it is then mixed with three parts of nitrum,[[49]] by weight or by measure, and after melting is transferred to other furnaces. In these the substance, now known as ammonitrum, is melted and then cast into cakes. These cakes are again fused to obtain pure glass and cakes of white glass.’
Pliny, in this confused account, where we have apparently materials from different sources imperfectly welded together, appears to contrast an older method of manufacture, practised formerly at Sidon, whose glass-works he seems to refer to as things of the past, with the newer processes now in use in Italy. It will be noted that in both cases a preliminary frit was prepared, although the term ammonitrum, a word of Greek origin, is applied to this frit in the latter case only.
‘Already,’ says Pliny, ‘the new art of melting sand with soda (literally “of tempering sand”) has spread through Gaul and Spain.’ He then goes on to tell, but with an expression of incredulity quite unusual with him, the story of the discovery of a malleable glass. According to this tale (in its earliest form), Tiberius ordered the workshop of the man who so tempered glass that it became flexible, to be pulled down, lest the value of bronze, silver, and gold should be depreciated. This story was the delight of the renaissance writers on glass. With regard to the more amplified and tragic version usually quoted from Petronius, we must remember that the remarks put by that writer into the mouth of Trimalchio are not always to be taken seriously. In later days a similar tale was told of a French inventor—in this Richelieu takes the place of Tiberius. After mentioning the calices pteroti, the costly ‘winged cups’ of Nero, Pliny gives some account (quite out of its proper place, by the way) of obsidian, a black stone much resembling glass, which was shaped not only into various dishes for use at the table, but also into figures of some size—statues of the divine Augustus, for instance, for that monarch much prized the material. Vitrum hæmatinum, ‘a red opaque glass,’ is passed over rapidly. ‘White glass is made also, and murrhine and glass resembling the hyacinth and the sapphire and glass of all other colours.[[50]] There is no substance easier to work or to which brighter colours can be given. The highest place must, however, be accorded to the white transparent glass which much resembles crystal; for drinking, it has driven out vessels of gold and silver.’ This passage is of the greatest importance. We see that a pure white glass was still, even in Pliny’s time, something noticeable. This was, as we shall see, again the case at the time of the Renaissance, when it was the aim of the glass-makers, all over Western Europe, to imitate the Vetro di cristallo of the Venetians.
It will be noticed that Pliny makes no mention of the method of preparation of the alkali used in making glass (in ‘tempering the sand,’ as he puts it). From the context it would seem that the nitrum was always of the same nature as that brought by the mariners to the Phœnician coast—this is, however, very unlikely. Nor have we any information about the arrangement of the furnaces. These glass houses were, however, well known to the beggars and loungers of the time—we hear of them as places of resort in cold weather for those who had no other way of warming themselves. In the Greek Anthology (No. 323), of all places in the world, there is a fragment by one Mesomedes, a contemporary and favourite of Hadrian, giving an account of a visit to a glass-house. Just at the point where the little poem breaks off, the workman is described as placing the molten mass between the blades of the pincers or shears.
Strabo tells us that when he was at Alexandria—he was there, we know, in the early part of the reign of Augustus (circa 24 B.C.)—he was assured by the glass-workers (ὑαλουργοί) that their ‘many-coloured and sumptuous glass’ could not be made without the addition of a certain glassy earth which was only found in Egypt, a story which points to the jealousy of foreign competition on the part of these craftsmen. So on the Phœnician coast he hears from some of the wonderful qualities of the Sidonian sand, while others tell him that one sand is as good as another. Strabo goes on to speak of the improvements made ‘quite lately’ in the clear crystal glass of which the manufacture had not long since been established at Rome. Compare with this the account of Pliny; in view of his certainly rather vague statements, we should hardly have looked for this cristallo in Italy at so early a date.
But it is neither from Italy nor from the countries bordering the Eastern Mediterranean that the most important supply of Roman glass has been obtained. Putting aside objects of quite local provenance, it will be found that in the museums of England, France, and Germany, by far the larger part of the glass exhibited—and this is above all the case with the blown glass—has been found within the limits of the ancient Gallia. Spain, contrary to what we might have expected, has yielded little Roman glass of any artistic merit, partly perhaps for want of systematic search. But there are few districts in France or in the west of Germany where the exploration of Roman cemeteries has not yielded a plentiful crop. If we travel northward from the estuary of the Rhone by way of Arles and Nismes to Avignon, Valence, and Lyons, then across by the country on either side of the Jura to the valley of the Rhine, and follow that river by Strassburg to Cologne, we pass for the whole way through a district especially rich in Roman glass. And this is what might well be looked for. The third and fourth centuries—a little earlier or a little later, according to locality—are above all the great centuries for the prevalent use of glass, and it was during this period that the central tract of country that included the two great metropolitan cities of Arles and Trèves began to take the prominent place that it maintained throughout the early Middle Ages.
Even our English glass of this time, so much of which comes from districts to the north and the south of the estuary of the Thames, may be brought commercially at least into connection with the wealthy provinces of Northern and Eastern Gaul. It was from these provinces that glass was first imported, and from them, no doubt, the glass-workers passed over to Britain.
In the case of the rich collection of Roman glass in the British Museum, the backbone, as it were, is formed by the specimens excavated from tombs in the neighbourhood of the lower Rhone valley—from Vaison, near Vaucluse (the Comarmond collection), from Apt, and from Alais. At Arles, in that district of tombs, the Aliscamps, which furnished Dante with a well-known image, beneath the Christian sarcophagi (in these, too, not a little glass has been found), the earlier Roman tombs lie on the bed-rock. From these tombs numberless urns of glass, in cases of lead or stone, have been taken, as well as many examples of glass of rare and exceptional shapes—among others what is apparently an alembic for use in distillation. Some of these vessels contain a red liquid which may represent at least the wine with which they were originally filled (Froehner, p. 109). In this town of Arles, too, in the suburb of Trinquetailles, there were probably extensive glass-works, as we may infer from the quantity of vitrified paste there found (Quicherat, Revue Archéologique, xxviii.).
To pass to the Roman cemeteries of Lyons: in the museum of that town are some curious masses of blue frit taken lately from a tomb on the Fourvière, which call to mind the fritted cobalt or smalt exported in modern times from the Saxon mines. We have in the British Museum many pieces of glass from older explorations at the adjacent suburb of St. Irénée. There is in the Lyons Museum a sepulchral stele of much interest found in this very district; it is to the memory of a certain Julius Alexander, a citizen of Carthage, a craftsman in the art of glass (opifici artis vitreæ). This Punic glass-blower left behind him children and grandchildren, who doubtless followed his trade. We must not infer too much from a single instance; we know, however, from other sources,[[51]] that there was a large influx into Gaul at this time of Semitic people, chiefly of a humble status, craftsmen and small merchants, and that they found their way in above all by the valley of the Rhone. These ubiquitous traders are generally referred to as Syrians, and I think it likely that the glass trade, not only in the south of Gaul but further afield, may have been in great measure in the hands of Orientals of this class. This would be especially true of the manufacture and hawking about of small objects of verroterie,[[52]] and again of glass pastes containing lead. But perhaps also the preparation of the more ambitious and artistic kinds of glass was in the same hands, leaving only the common ware to the native workmen; in that case the distinction so important in later days between the cristallo and the ‘forest-glass’ may have had its prototype in Roman times. It should be borne in mind that these Semitic craftsmen would for the most part speak Greek rather than Latin, an important point that I have not space to develop here.