Old Glass and How to Collect it

by J. Sydney Lewis

In England, as we shall see, glass was made during the Roman occupation. Under the Saxons, glass-workers were imported from the Continent, but to judge from the number and variety of the specimens found in Anglo-Saxon tombs, it is probable that it was also manufactured to an equal extent at home. During the Middle Ages the art appears to have fallen into abeyance, save in a few isolated instances to be noted later, but in the sixteenth century the custom of using glass vessels was introduced from France and the Low Countries, most of the pieces being imported from Venice. To prevent the money thus expended from leaving the country, efforts were made about the middle of the century to establish the art by the aid of workmen from Murano, and the history of glass manufactured in England may be said to have fairly begun. It was undoubtedly stimulated by the religious persecutions on the Continent, particularly the Spanish Terror in the Netherlands, for the Low Countries were seriously endeavouring to rival Murano in the art, and the craftsmen who fled for refuge to England undoubtedly did much to develop their trade in the country of their adoption, as did the Huguenot refugees at a later period.

Fig. 39.

In the seventeenth century the whole process was revolutionised by the introduction of a large proportion of oxide of lead, making what is technically known as “flint” glass—a glass much more brilliant than any other, a quality due partly to its transparency and partly to its increased refractive power, which renders it specially fitted for “cutting”—a process which enhances its beauty by increasing the number of ways in which the light rays falling on the glass are dispersed. The discovery has given English glass a well-deserved pre-eminence for beauty of metal—a pre-eminence which the glass-cutters of the eighteenth century admirably sustained by the excellence of their work.

All this time the art of glass-making on the Continent had been developing. In particular, the Venetian workers at Murano had perfected the art of colouring and enamelling glass—a result which was later to have its influence upon English artists. An admirable example of what they achieved in this direction is an old spinet in the South Kensington Museum, which once belonged to Queen Elizabeth of Bohemia, the daughter of James I. Whatever its merits as a musical instrument, its once gorgeous gilt crimson leather case hides an interior of the utmost interest to students of glass, for the interior of the lid is panelled into eighteen divisions, each representing some classical subject—Narcissus, Daphne, Andromeda, Argus, etc.—admirably done in coloured glass. The front of the keyboard, the stretcher bar and the keys themselves are also elaborately decorated in similar fashion with coloured glass, silver or enamel. The keys are covered with ornaments in coloured glass, the accidentals being faced with blue and white striped glass and the naturals being fronted with the same.

Although it is no part of the purpose of this book to deal in detail with the technical side of the manufacture of glass, yet some few words as to the nature of the material with which we are dealing are not only desirable but essential to the proper understanding of its various qualities and kinds and the different stages of its manufacture.

The scientist will tell us that glass is a double silicate, being compounded of a silicate of sodium (or potassium) and a silicate of lime. For the benefit of non-scientific readers, we may remark that a silicate is a chemical compound formed when silica combines with an alkaline substance like lime, soda, or potash. Silica is probably the most widely distributed substance in nature. Silicate of alumina is, for example, the basis of all clayey soils, and silica, in the pure form of quartz, is the chief constituent of the sand of the sea and of all those rocks which are known as sandstones. Rock-crystal, amethyst, agate, onyx, jasper, flint, etc., are all varieties of silica. Crystalline silica is hard enough to scratch glass—a fact utilised, as we shall see, in the sand-blast which is used for the purpose of engraving patterns on glass. Silica is fusible only at a very high temperature, but readily combines with alkaline substances to form soluble silicates, which are known in commerce as soluble glass, or water-glass, because it dissolves readily in hot water. Water-glass is used in making artificial stone, in coating stone surfaces, e.g. walls of buildings, etc., to preserve the stone from decay under the weathering influence of the atmosphere, and in the manufacture of cement.

Ordinary glass has many valuable properties which make it of great importance in the arts and manufactures. Among these may be mentioned the fact that it can be made to take any shape with ease. It resists the action of all ordinary acids, and hence is of the utmost value to the chemist and the chemical manufacturer. Hydrofluoric acid alone attacks it, by combining readily with its silica and so dissolving it. For this reason, hydrofluoric acid is used in etching on glass. Again, glass is cheap, being literally made from the dust of the earth; it is transparent, and so can be used in buildings, transmitting light whilst protecting from the inclemency of the weather. Its transparency, too, combined with its high refractive power, make it of inestimable value in the manufacture of optical instruments. It is this high refractive power, too, which gives to cut glass its beautiful lustre and sparkle, and one aim of the glass-founder is to increase this refractive power and so enhance the brilliancy of his product. If glass could be made which would refract light to the same extent as the diamond does, it would exhibit the same “fire” as the king of gems. It is hard and close in texture, and so is capable of taking a high polish. Its great drawback is its brittleness, but this can be reduced to a great extent by immersing it, whilst red-hot, in a hot bath of paraffin oil, wax, or resin. A tumbler of glass so “tempered” may be dropped on the floor without breaking.

It may be added, as a matter of common interest, that this brittleness is largely a result of the fact that glass is an extremely bad conductor of heat. Because of this, a mass of molten glass, when cooling, becomes set on its outside surface long before the interior has become solidified; hence the solid exterior prevents the molecules of the interior portion from contracting. As a result, a condition of strain is established, the interior molecules tending to contract, while the exterior tends in the opposite direction; consequently a very slight blow is enough to cause a fracture.