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Chance Brothers, to assist in reproducing pot-coloured glass. Bontemps made considerable advances in the rediscovery ofancient techniques, and explained the significance and complexity of oxidation to the British glass manufacturers.
19th century experimentation led to the development ofnewtypes of coloured glass, as increased demand encouraged further innovation. By the 1850s, patent rolled cathedral glass, either coloured or clear, was marketed for its “rich and brilhiantappearance inaChurch Window, whichcannotbe arrived atwith ordinary Coloured Glass”. (Hartley & Co. Glass Tar~ffNewspaper, 1 November, 1853, p 10). Cathedral glass was rolled either on a table or between two rollers, and by using a textured surface a pattern could be transferred to the glass. New colours were also developed, as the following description illustrates: “The ordinary shades ofgreen are the product of oxides of iron and copper in different proportions, the yellow tints being due to the iron, and the blue tints to the copper. The carburet (with carbon) gives adull yellowcolour; blue is produced by the oxide of cobalt; purple by the oxide of manganese; and the varieties of rose and ruby by the oxide of gold; topaz is given by the oxide of uranium; and emerald green by the same metal, with the addition of a small quantityof copper. Glass is rendered opaque bythe addition ofarsenic; and the peculiar colour of the opal is produced by the phosphate of lime. The quality of all colour in glass is the result of a proper degree of heat during the fusion of the materials.” (Official Descriptive and illustrated Catalogueofthe GreatExhibition, 1851, p.704)
In 1878, the Universal Exhibition in Paris first brought the work of Louis ComfortTiffany to a European audience.


GLASSAT UPPARK
The award winning restoration of his- toric Uppark on the Sussex Downs, dam- aged by fire in 1989, has benefited from the traditionaiglass blowing skills of one of Saint-Gobain’s factories in the upper Loire region ofFrance to create authentically glazed Georgian windows. The Verrerie de SaintJustfactory, which pro- duced the restoration glass, began life in 1826 manufacturing champagne bottles using local sand from the river Loire and coal out ofthe Saint-Etietme mines. Since 1865 ithasproduced nothing but mouth blown, drawn and moulded glass for decorative and practical applications.
The mouthblownglass installedin 56 windows throughout Uppark House has occasionalbubbles andfme scoring. This matches the appearance of original
Tiffany had been experimenting with coloured glass in America, and had developed something entirely new:
iridescent and opalescent glass. Although he used this type of glass primarily for lamps and vases, Tiffany also produced highly detailed coloured glass panels, and continued to develop opaque, textured and multi-coloured glasses for his distinctive decorative windows. One type ofglass, called Favrile and patented by Tiffany in 1894, was composed of several colours of glass pressed together in layers while hot. British glassmakers andglassartists ofthetimewere inspired


The oxides used in an oxidising furnace (fusmg with the glass to form a col oured sthcate) are the following
El Cobalt very small amounts (0 025 0.1%) are required to produce a good blue When combmedwith magnesium orzinc, cobaitwifiproduce redorgreen. E Copper only 2 3% of fully oxidised copper oxide is required for copper blue/copper green. The colours pro- duced (blue, green or red) depend on other oxides present Lead oxide for example, will give green. Sodium or potassium oxides present will produce turquoise blue. Thus the translucent


cylinder glass, few panes of which survived the devastating 1989 fire. The SaintJust glass is produced by shaping it to form a cylinder before being split along its length, re-heated and flattened to a nominal 2 mm thickness. The flat glass is carefully annealed for almost two hours after, to remove all stresses and make it suitable for subsequent cutting in sizes up to 1 m.
Projectarchitectlain McLaren of the Conservation Practice said: “Theglasssupplied is a perfect match for the original and gives the building a sparkle andvitalitywhichis such an essential feature of 1 8th century ele
by these innovations, and produced marbiedandopaqueglassesin imitation ofTiffany glass.
The Editorwould like to thank the Glasgow West Conservation Trust for permission to reproduce this secton from the excellent Conservation Manual series of conservation guides currently being published by the Trust. The series cur- rently includes: Principles &Practice of Conservation (44pp); Stonework (6Opp); Ironwork (52pp) and Decorative Domestic Glass (68pp). A guide to Rot & Insect Infestation is to be published shortly. Futher information about the series can be obtained from the Lynne Carson Rickards, Glasgow West Conservation Trust, 30 Cranworth Street, Glasgow G12 8AG. Tel: 0141 339 0092.


vations. The NationalTrustis committed to using authentic materials andmethods wherever possible and it was truly gratifying to fmd that ancient techniques ofglassmanufacture, thoughtbymanyto be obsolete, are still being carried out.” The completed restoration won a special Civic Trust CraftsmanshipAwardinJune.
METALUC OXIDE COLOURANTS
The oxides used in a redueing furnace
(creating a suspension of metallic part
des in the glass) are:
ElSilver silverstam composedof silver
sulphide or nitrate, produces a range of
colours from pale yellowto orange-red.
~ Gold 0 001% of gold in a reducing
furnace produces ruby glass
~ Copper: reduced coppergives a dark,
opaque red also described as ruby This
was known byatleastthel2th century,
and was so dense that ‘t pane only 3mm
thick would appear black.
~ Iron in reducing conditions iron
creates a dark blue or green
cerulean blue of ancient glass was
LI Tin tin oxide produces an opaque
produced by the combination of soda
white. The ancient glassmakers added
Wind copper carbonate in the glass
antimony to the molten material to
batch
achieve this The oxides of arsemc and
LI Iron 05 1% of iron oxide will pro-
tin were introduced by Venetian crafts
duce iron blue Additional oxygen can
men to imitate the opaque white of
result in ~ ellow/amber while green is
Chinese porcelain
the result at different degrees of oxida
Modern chemistry has produced a
lion and black is produced when the
new range of colours for glass The new
concentration of iron is 10% or more
metals used mclude titaniumforyellow
LI Manganese 26% of manganese ox
brown selenium for red nickel for
ide will produce a purple brown The
purple blue brownorbiack ehromium
colour fades when the furnace tern
for yellow green and fluorspar and
perature exceeds 1200 C
zirconia for opaque white
CONTEXT 48

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