There follows on this what is perhaps the earliest extant description of a glass furnace. ‘The furnace of the glass-makers should have six compartments, of which three are disposed in stories one above the other.... The lower compartment should be deep, in it is the fire; that of the middle story has an opening in front of the central chambers—these last should be equal, disposed on the sides and not in the centre (?), so that the fire from below may rise towards the central region where the glass is and heat and melt the materials. The upper compartment, which is vaulted, is arranged so as uniformly to roof over the middle story; it is used to cool the vessels after their manufacture.’[[85]] We have also the description of a smaller furnace, which is perhaps that in which the more fusible glass for enamels and minor objects of verroterie was melted. Finally, an oven with a floor of brick-earth is mentioned, for fritting the sand and alkali. In spite of much that is obscure in this description, we can trace in it the general type of furnace which, doubtless handed down from Roman times, has survived in places with few important changes to the present day.
MEDIÆVAL GLASS FURNACE
FROM AN ILLUMINATED MANUSCRIPT OF RABANUS MAURUS
And here I may call attention to a contemporary drawing of a mediæval glass furnace—a source of information as unique as it is unexpected. This is to be found in a manuscript of an encyclopædic work, De Originibus Rerum, compiled by Rabanus Maurus, one of the earliest of the schoolmen. Rabanus lived in the Benedictine monastery of Fulda, in the first half of the ninth century. The manuscript in question, which is attributed to the year 1023, has been carefully reproduced by the monks of Monte Cassino where it is preserved. The full-paged miniature is to be found in a chapter headed De Vitro; I can, however, discover nothing in the text that throws any light on our subject. In the illustration we see to the left a nearly naked workman who holds a mass of some green material, perhaps the frit; another man is blowing through a tube what is probably meant for the unfinished cup; to the left a chalice-like vessel, perhaps the model, is depicted. Notice, too, in the pediment of the roof (probably to be regarded as the annealing oven) a cup with a knob for stem, and hemispherical foot. Cups of a similar form, apparently in these cases of metal, are found in other illustrations of the manuscript ([Plate XIX.]).
M. Berthelot has reproduced in his earlier work (La Chimie des Anciens) several rough pen-sketches of the apparatus used by the mediæval alchemists, taken from the St. Mark’s manuscript mentioned above. These drawings help us in a measure to understand the important place taken by glass vessels of various forms in the researches of these early experimental workers. Still more interesting are the illustrations in the Syriac manuscript from which I have just quoted; in these, the modern chemist may recognise many familiar forms. The glass vessels have chiefly reference to processes of distillation. The most important is the alembic, a form easily made; the neck of a long pendulous paraison has only to be heated on one side near the base, when it falls over of itself to assume the well-known shape. We see also flasks, standing in water or sand baths, within which various substances are digesting; in other cases the contents are volatilising into the turban-shaped aludels placed above them.[[86]]
But in all this strange literature, which, starting from the banks of the Nile in the first centuries of our era, spread over the Byzantine empire and was so eagerly absorbed by the first Arab conquerors, the interest in glass is only of a secondary nature,—the great question was the transmutation of matter and the consequent preparation of gold. Glass, as I have said, was of importance chiefly as a means to that end.
It was far otherwise with the writer whose work we must now examine. Theophilus, the author of the Schedula Diversarum Artium, was, it would seem, a monk in the monastery of Helmershausen, not far from Paderborn, in the old Saxon land. The earliest manuscript of his work probably dates from the twelfth century; it is preserved in the famous library at Wolfenbüttel. The treatise itself may perhaps be referred to the end of the eleventh or to the beginning of the next century; but in spite of this early date the style of the book is modern compared with the mediæval compilations we have lately been considering. That the German monk Rugerus, or Rogherus, should have assumed the Greek name Theophilus is itself a significant fact. He was, it would seem, a hard-working goldsmith and a ‘skilled artificer’ in many branches of the arts. He drew his inspiration from the Byzantine East on the one hand, and on the other from the younger civilisation that was beginning to centre in the new kingdom that was growing up in and around the Isle de France. To these sources we must perhaps add the older Cluniac tradition: from Tuscan artists also he had something to learn.[[87]]
‘Theophilus, an humble priest, servant of the servants of God, addresses his words to all who desire by the practical work of their hands and by the pleasing meditation of what is new, to put aside and trample under foot all sloth of mind and wandering of spirit....’ In this book they will find ‘all that Greece possesses in the way of divers colours and mixtures, all that Tuscany knows of the working of enamels [electrorum operositate] or of niello [nigellum], all that Arabia has to show of works ductile, fusible, or chased, all the many vases and sculptured gems and ivory that Italy adorns with gold, all that France prizes in costly variety of windows, all that in gold, silver, copper and iron or in subtle working of wood and stone is extolled by inventive [sollers] Germany.’ We are here in a healthy northern atmosphere, far removed from the shuffling statements and ambiguous formulas of the oriental alchemists.[[88]]
The second book of the Schedula is concerned exclusively with glass, but most of the thirty-one sections deal with the preparation of stained glass for windows. In a curious passage to be found in the prologue of this book, Theophilus tells us that he has ‘approached the atrium of the Holy Wisdom [Agiæ Sophiæ] and beheld the cellula adorned with every variety of divers colours, showing the nature and use of each.’[[89]]