VITREOUS COLLECTION. 
127 
Flint Glass is composed of a mixture of silica, alkali, and 
■oxide of lead. Formerly the silica was introduced in the shape 
of calcined flints, whence the name “ flint ” glass, but at the 
present day sand alone is employed. The chief localities in 
England for glass-making sand are Alum Bay, Lynn, Aylesbury, 
Wareham, Reigate, and the New Forest ; but it is not always of 
sufficient purity for flint-glass manufacture. Large quantities 
are also derived from Fontainebleau, in France, and from 
America, Australia, and New Zealand. The sand is prepared 
for use by simple washing and calcining, or if necessary by 
treatment with hydrochloric acid. 
To remove the colour imparted to the glass by impurities in 
the raw materials, especially iron and carbon, certain oxidizing 
•agents are always mixed with the raw materials. Of these 
oxygen-yielding substances, the most common are nitre or salt- 
petre, arsenious acid or white arsenic, and pyrolusite or peroxide 
of manganese. An excess of manganese produces a violet 
colour ; and even when at first there is no appearance of colour 
in the glass, it will upon exposure to sunshine be gradually 
developed. Instances of this pink or violet tint are exhibited in 
the cases before us, and the same thing is strikingly shown by 
much of the plate glass in the roof of the building. 
The details of glass- working are illustrated by a series 
exhibiting the successive stages in the manufacture of a wine- 
glass ; and several of the simple tools of the glass-worker are 
exhibited, viz., the pucellas, the spring tool, and the wood tool. 
The mode of blowing glass in metallic moulds is also illustrated. 
Many of the specimens in Case 52 were used by the late 
Mr. Apsley Pellatt in illustration of his lectures at the Royal 
Institution, afterwards published under the title of “ Curiosities 
of Glass-making.’' (1849.) 
Among these specimens attention may be directed to an 
example of cameo incrustation of much interest. The figure, 
usually made of porcelain clay and sand which has been pre- 
viously fused with carbonate of potash, is formed in a plaster 
of Paris mould, and slightly baked. It is then heated to 
redness, and being placed within a cylindrical flint-glass pocket, 
the open end is heated and welded together by pressure, so that 
the figure is in the middle of a hollow hot mass of glass. The 
whole is re-warmed and the workman exhausts the air by his 
mouth from within, by means of the tube to which it is 
attached, and thus by atmospheric pressure the whole becomes a 
homogeneous body. 
An incrusted inscription is another example of a similar 
character ; the letters are drawn upon a piece of glass with a 
vitrified black paint, and burnt in ; the inscribed glass is 
introduced at nearly a red heat into a glass pocket, and treated 
as already described. 
Case 52 also includes a series of modern Venetian enamel 
cakes , and a collection of glass beads used in the African and 
