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Some glassworking techniques employed by Gallé
A very important characteristic of the Art Nouveau style was the unwavering
attention that exponents of this tendency displayed towards their material,
its natural properties and experiments in the sphere of technique. The
multi-layered glass technique that Emile Gallé used enabled him
to create a distinctive version of glass painting. The superimposing of
layers of different-coloured glass produced complex shades, transitions
from one colour to another, a combination of clear and matte glass depending
on the artist's will. This method was not invented by the members of the
Nancy school, as far back as Ancient Greece it was frequently used to
imitate cameos. In the 19th century it was revived in England. In Nancy,
however, this technique was given an entirely new and more complex artistic
interpretation. The glass was etched and ground in several stages, with
engraving and glass inlay also being used. The surface of the glass too
was treated in a variety of ways. It could, for example, be not polished
but ground on a special wheel; the glass retained the immediacy of hand-work,
as if the artist had carved the vase from stone. Enamel powder was sometimes
applied to the surface of the glass, rendering it smoky and more complex
in colour when fired. Often the glass was matted by some chemical means
which led to a specific dulling of the colour. A design might be engraved
in various layers. Sometimes highlights were introduced using metal oxides.
And that is by no means a complete description of the technical arsenal
employed by the Nancy school.
Melting glass
A process carried out in a glass furnace, as a result of which the loose,
powdered components of the charge are fused into a molten mass of glass.
The temperature required for this is no less than 1500 degrees Celsius.
The cycle of producing raw glass in a crucible furnace and then creating
objects from it takes a matter of days.
Mould-blowing
The formation of items from molten glass by hand using a special tube,
called a blowing iron, pontil or punty. This method was invented at the
turn of the Christian era and remains the main one for the production
of artistic glassware. To produce the desired shape a bubble (or parison)
of glass is blown to expand it while inside a mould made of wood or metal.
There are two means of mould-blowing, depending on whether the glass is
turned or not.
Multi-layered glass
Glass consisting of two or more layers of glass of differing colours,
the main one of which is transparent. Depending on the number of layers,
such glass is described as two-layered, three-layered or multi-layered.
Depending on the relative positions of the transparent and coloured layers,
experts speak of over-colour and under-colour. This type of glass is known
from Roman times and from 18th-century China.
Multi-plane etching
A technique used to decorate multi-layered glass by using hydrofluoric
acid to remove coloured glass to varying depths in the required places
with a result that resembles watercolour painting.
Etching
The treatment of the surface of the glass with hydrofluoric acid, producing
a matting effect that can range between slight and strong. In this technique
the surface of the piece is covered with wax or some other protective
coating into which a design is scratched, then the acid is applied to
the object using a brush or by immersion. Experts distinguish matte etching,
light etching and multi-plane etching. The properties of hydrofluoric
acid were exploited on isolated occasions in Germany as early as the 18th
century. It is known in Britain from 1830 and in the late 19th and early
20th centuries it was extensively used in European glassmaking to produce
both one-off items (Gallé) and for mass-produced articles.
Engraving
A method of decorating a glass surface by scratching it with some sharp
instrument. There are two types of engraving depending on the method used.
The first is diamond engraving, when the design is applied by scratching
or tapping the surface with a diamond-tipped cutter. This produces a very
fine design that looks lighter than the smooth glass ground. The second
method involves the use of a copper wheel. Emile Gallé used diamonds
to engrave his articles.
Marquetry
A decorative technique is which hot coloured glass is pressed into the
surface of a glass object is such a way that its surface remains smooth.
Zwishengoldglass
A decorative technique using gold foil. The sheet of gold is sandwiched
between two layers of glass.
Cutting
A general term for mechanical means of treating the surface of glass items
by making deep cuts on its surface using a rotating abrasive of iron wheel.
Coloured glass
Glass given a particular colour by the introduction of special chemical
components into the furnace charge. The colouring can be either molecular
or colloidal. Molecular colorants are metallic oxides. The colour of such
glasses remains unaffected by subsequent heat treatment. Glasses coloured
by the colloidal method include gold rub y, copper and cadmium. Depending
on the temperature used in making the glass or subsequent heating the
intensity of colour of such glasses may vary, or they may become transparent.
Different combinations of colorants and temperatures make it possible
to produce more elaborate shades of glass.
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