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Chance Brothers, to assist in reproducing
pot-coloured glass. Bontemps made
considerable advances in the rediscovery
of ancient techniques, and explained the
significance and complexity of oxidation
to the British glass manufacturers.
19th century experimentation led to
the development of new types 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
brilliant appearance in a Church Window,
which cannot be arrived at with ordinary
Coloured Glass”. (Hartley & Co. Glass
Tariff Newspaper, 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 of green 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
a dull yellow colour; 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 quantity of copper.
Glass is rendered opaque by the addition
of arsenic; 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
Catalogue of the Great Exhibition, 1851,
p.704)
In 1878, the Universal Exhibition in
Paris first brought the work of Louis
Comfort Tiffany to a European audience.


GLASS AT UPPARK
The award winning restoration of his-
toric Uppark on the Sussex Downs, dam-
aged by fire in 1989, has benefited from
the traditional glass blowing skills of one
of Saint-Gobain’s factories in the upper
Loire region of France to create authenti-
cally glazed Georgian windows. The
Verrerie de Saint Just factory, which pro-
duced the restoration glass, began life in
1826 manufacturing champagne bottles
using local sand from the river Loire and
coal out of the Saint-Etietme mines. Since
1865 it has produced nothing but mouth
blown, drawn and moulded glass for
decorative and practical applications.
The mouth blown glass installed in 56
windows throughout Uppark House has
occasional bubbles and fine 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 of glass, called Favrile and patented
by Tiffany in 1894, was composed of
several colours of glass pressed together
in layers while hot. British glassmakers
and glass artists of the time were inspired


The oxides used in an oxidising furnace
(fusing with the glass to form a col
oured silicate) are the following
-  Cobalt very small amounts (0 025
0.1%) are required to produce a good
blue When combined with magnesium
or zinc, cobalt will produce red or green.
-  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
Saint Just 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.
Project architect Iain
McLaren of the
Conservation Practice
said: “Theglasssupplied
is a perfect match for
the original and gives
the building a sparkle
and vitality which is such
an essential feature of
1 8th century ele-
by these innovations, and produced
marbled and opaque glasses in imitation
of Tiffany glass.
The Editor would like to thank the Glasgow West
Conservation Trust for permission to reproduce
this section from the excellent Conservation
Manual series of conservation guides currently
being published by the Trust. The series cur-
rently includes: Principles &Practice of Conser-
vation (44pp); Stonework (6Opp); Ironwork
(52pp) and Decorative Domestic Glass (68pp).
A guide to Rot & Insect Infestation is to be
published shortly. Further 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 National Trust is committed
to using authentic materials and methods
wherever possible and it was truly
gratifying to find that ancient techniques
of glass manufacture, thought by many to
be obsolete, are still being carried out.”
The completed restoration won a special
Civic Trust Craftsmanship Award in June.
METALIC OXIDE COLOURANTS
The oxides used in a redueing furnace
(creating a suspension of metallic part
des in the glass) are:
-  Silver silver stain composed of silver
sulphide or nitrate, produces a range of
colours from pale yellow to orange-red.
-  Gold 0 001% of gold in a reducing
furnace produces ruby glass
-  Copper: reduced copper gives a dark,
opaque red also described as ruby This
was known byatleastthel2th century,
and was so dense that a pane only 3mm
thick would appear black.
-  Iron in reducing conditions iron
creates a dark blue or green
cerulean blue of ancient glass was
-  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
-  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 yellow/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 include titanium for yellow
- Manganese 26% of manganese ox
brown selenium for red nickel for
ide will produce a purple brown The
purple blue brown or black chromium
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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