DECORATED GLASSWARE
Certain methods of decorating glass are carried out whilst the glass is
being made by the workmen. Other methods consist in decorating the glass
after it has been made, such as cutting, fluting, etching, engraving,
and enamelling. In another form of decoration the method consists of a
combination of two or more of the above processes. The crystal glass may
be cased over with a thin covering of coloured glass by the glass
worker, and this outer coloured casing cut through by the glass cutters,
exposing and showing through the colourless crystal underneath with very
effective results.
A small portion of coloured glass, such as citron green, topaz, blue, or
ruby metal is gathered from the pot by an assistant, and the workman,
gathering a ball of crystal glass on his blow-iron, allows a portion of
the coloured metal held by the assistant to fall or drop upon the ball
of crystal. Upon blowing the whole out, the coloured metal is spread as
a thin casing upon the outside of the bulb of crystal. This bulb is then
worked into a wine-glass or other article, which, after annealing, is
sent to the glass cutter, who decorates the outer surface by cutting the
glass on his wheel. The colourless glass then shows through against the
coloured surface where it has been cut to the pattern, the colour
standing out in relief.
In another form of decoration, the workman allows small pear-shaped
tears or drops of coloured glass to fall upon the outer surface of a
bowl or vase, in equidistant positions round the circumference of the
article, By placing and working the coloured glass into position in this
way, some pretty artistic results are obtained, dependent upon the skill
and artistic taste of the workmen.
In another method of decoration, certain coloured glasses are used, the
composition of which causes them to turn opalescent upon re-heating the
glass to a dull red heat. The re-heating of the tops of crimpled flower
vases made from such glass gives pretty results, showing a gradual
fading opalescence, extending from the top edges to a few inches down
the vase, into a clear coloured glass at the foot of the stand. A
similar effect, without the opalescence, is obtained by the workman
gathering a small piece of coloured glass on the tip of his blow-iron,
and then taking a further gathering of clear crystal metal. The whole is
then blown out and worked into a vase or wine-glass, thus obtaining a
coloration denser at the top edges, where the vase or wine-glass has
been sheared off, and gradually fading away to a colourless glass a few
inches towards the foot, which is clear crystal.
There are also certain compositions which, when worked into a vase, and
re-heated on the edges, strike or turn to a colour such as pale blue or
ruby. These are self-coloured glasses, in which the colouring remains
latent until the glass is re-heated, like the opalescent glasses. In
these glasses the composition is the more essential factor.
=Glass cutting= is an effective way of decorating glassware. In using
this method, the crystal glassware is made fairly heavy and strong, so
as to permit of the deep cuttings which refract the light and show up
the prismatic patterns so brilliantly.
[Illustration:
MACHINE FOR SMOOTHING BOTTOMS OF TUMBLERS
]
In cutting glassware, the glass cutter works in front of a rotating disc
of iron carried in a frame. This wheel has a bevelled edge upon which a
fine jet of sand and water is allowed to drip from a tundish above. The
abrasive action of the sand cuts into the glass, and the workman, by
holding the glass dish or bowl against the wheel, follows the design or
pattern in diagonal lines across the article. These cuttings are
recrossed, and the intermediate diamond spaces filled in with lightly
cut set patterns, until the whole of the intended design is “roughed”
out over the surface of the glass, after which the glass is taken to
another frame carrying a stone wheel, which is of much finer abrasive
action. This stone wheel smooths the rough cuts done by the previous
wheel. After this the cuts are polished successively on a wood wheel and
brush with polishing powders, until a smooth and polished cut is
obtained.
As the value of the glass is greatly increased by cutting, only the best
and clearest articles of table glass are so treated. The work of cutting
becomes technical and expensive, according to the richness of the
cutting demanded. The crystal table glass made from lead gives the most
brilliancy in cutting. Soda-lime glasses are found to be hard to cut and
do not give such brilliant and prismatic effects as the glass made from
lead compositions.
An automatic machine for grinding, smoothing, and polishing the bottoms
of tumblers, etc., “bottoms” or grinds, smooths, and polishes tumblers
at the rate of 2,000 a day. Four vertical revolving wheels are fixed
within a frame, one iron, two stone, and one wood. Over each of these is
a rotating spindle carrying the tumbler so that the bottom of it is
automatically pressed against each vertical wheel in turn. The first
wheel does the roughing, the two next the smoothing, and the fourth the
polishing. These machines are simple and require only unskilled labour
to operate, and go far towards cheapening production.
=Glass engraving= and intaglio work is a much lighter and more artistic
method of decorating glass than the deep cutting before described. In
these processes the glass is cut or ground to a less extent, and a more
free treatment of design is possible. Floral ornamentation and natural
forms of applied designs can be carried out, and portions may be left
rough or polished, according to the effect of light and shade required.
The workman, whilst engraving, works before a small copper or metal
wheel rotating in a lathe, and uses fine grades of emery or carborundum
powders made into a paste with oil, as the abrasive medium. The frame
turning these wheels is like a lathe, and may be worked by a foot
treadle. The wheels are interchangeable, and an assortment of various
sizes, having different bevelled edges, is kept at hand in a case, from
which the engraver selects the one most suitable for the particular work
to be done.
Glassware for engraving and intaglio may be made much lighter than that
required for cutting.
=Etching= is a method of decorating glass by the chemical action of
hydrofluoric acid. This acid in its various combinations attacks glass,
decomposing its surface and giving a dull or semi-matt effect. Only
those portions of glass which constitute the design are exposed to the
acid paste or fumes. The other portions are protected by a covering of
beeswax, which is unaffected by the acid and protects any portions
covered by it.
[Illustration:
GLASS ENGRAVING
]
The process carried out is varied in many ways. In some cases pantograph
and etching machines are introduced to give the designs. A warm copper
plate, with the design or ornament engraved thereon, is covered with a
wax paste, and the surplus cleaned off with a palette knife or pad of
felt, leaving the paste in the recesses of the engraving; a piece of
thin tissue paper is laid over the engraved plate and takes an
impression of the design in wax. This tissue is then transferred to the
glass to be decorated, the wax design adheres to the glass, and the
paper is drawn away. A further resist or coating of wax is painted round
the design to protect the rest of the glass, and a paste composition
giving the action of hydrofluoric acid is applied, which after a short
time eats into the exposed portions of glass. After another short
interval, it is washed off, and the wax coating removed by washing the
glass in hot, soapy water. The design then appears in a matt state
against the clear, unattacked glass.
The mechanical method of etching the design is carried out by first
dipping the whole glass into a bath of hot liquid wax, allowing a thin
coating to set and cool upon the surface of the glass. The article is
then introduced into a machine which has a number of needles, worked by
sliding gears in an eccentric fashion. These needles are adjusted just
to scratch away the thin coating of the wax into a design, and expose
the glass in the form of a decorated scroll or band round the glass. The
glass is then dipped into a vat or bath of dilute hydrofluoric acid for
a few minutes, after which it is removed and washed, and the wax
recovered by heating the glass upon a perforated tray, when it melts and
runs off the glass, and is collected for further use. The article is
then washed and cleaned and shows the scroll or etched portions where
the needle has traced the design. Another effective result is obtained
by etching a design on the back of a plate glass panel. After cleaning
and silvering or gilding the back, the design appears in a matt silver
or gilt lustre upon viewing it from the front of the mirror.
Glass which has been sand-blasted has a similar appearance to etched
glass, but a rather coarser surface. The portions of the glass plate to
be decorated are exposed to the action of a blast of air, into which
fine, sharp-grained quartz sand is automatically fed. An abrasive
action, due to the force with which the particles of sand are blown
against the glass, takes place, rendering the surface opaque or matt.
This method is generally adopted in printing trade names or badges upon
bottles, etc. A stencil of parchment or lead foil is cut out to form,
and used to protect the glass and resist the abrasion where required.
Rubber gloves are worn by the operator. The work of sand-blasting is
executed within a small enclosed dust-proof chamber fitted with glass
panels. The operator manipulates the glass through openings in the sides
of the chamber. The air blast is supplied by a motor-driven air
compressor and is regulated by a foot pedal. The action is very sharp
and quick, and is a cheap and effective way of badging hotel glassware
and proprietary bottles.
Glassware may be decorated by being enamelled with coloured enamels. In
this method of decorating, soft, easily-fused, coloured enamels are
used, containing active fluxes such as borates of lime and lead, which
melt at low temperatures. These enamel colours are prepared by being
fused and then ground to fine powders, which are mixed with a siccative
or oil medium, and painted upon the glass. The painted ware is then
heated within a gas or wood-fired enamelling furnace or muffle, until
the painted designs are melted and fused well upon the glass. The glass
is re-annealed in cooling down the muffle. For this form of decoration,
a hard refractory glass is required that will not soften easily under
the heat of the muffle; otherwise the glassware becomes misshapen too
easily under the heat necessary to flux or fuse the enamels properly.
A form of staining glass is also practised which consists of applying
compositions containing silver salts to portions of the glass and firing
at a low heat. The silver stains the glass a deep yellow. The colour may
be varied by the use of copper salts, when a fine ruby stain is obtained
wherever applied.
=Iridescent= glassware is produced by several methods. Sometimes a small
proportion of silver and bismuth is added to a coloured glass batch, and
by manipulating the resulting glass in a carbonaceous flame the silver
is partially reduced within the glass, forming a pretty iridescent
reflection on the glassware. By a suitable adjustment of the oxygen
content in the composition of such glasses, the iridescence can be
regulated to such an extent that the slightest flash or reducing
influence gives a beautifully finished lustre over the ware.
Iridescence can also be formed by re-heating crystal glassware within a
chamber in which salts of tin, barium, aluminium, and strontium are
volatilised. This method produces a superficial iridescence which is not
quite so permanent as the previous process.
=Glass Silvering.= The silvering of mirrors is carried out by taking a
thoroughly cleaned plate of polished glass and floating one surface in a
solution of silver nitrate, to which a reducing agent is added. The
silver is thereby precipitated or deposited in a thin lustrous film upon
the glass, which causes reflection by the rays of light striking against
the silvered background.
After silvering, the back of the plate is coated with a protecting paint
or varnish, which dries and preserves the silver deposit and gives it
permanency.
In the manufacture of fancy ornaments, such as birds, hat pins, and
small animals, various coloured glass cane and tube are worked together
by the operator melting and welding the respective colours together
before a blow-pipe flame, the tails of the birds being formed by sealing
in a fan of spun glass into the body of the bird, which has been blown
out and formed from a piece of tube. Some very curious ornaments are
formed in this way. Glass buttons, pearl, and bead ornaments are formed
by working cane and tube of various coloured compositions before the
blow-pipe, sticking and shaping the various forms on to wire.
Mosaic glass decoration is used in jewellery in a mural or tessellated
form. In this method small cubical or other shaped cuttings of various
coloured opaque glass are inlaid in mastic cements or pastes to form the
design, the face being afterwards ground and polished smooth, and
mounted or set within the ornament.
Larger cuttings may be inlaid in cement for pavement or mural
decoration.
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