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.

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.

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.