There are many different methods that have been used to produce a rough surface on glass, and some of them are difficult to distinguish. Basically they fall into two types, those which are applied by some treatment to the surface of the glass, and those which are applied via a mould. The first set includes sand-blasting, acid etching, crackle or ice glass or verre craquelle, overshot glass or broc a glaces or rugiadoso, and vetro corroso. The second category includes all kinds of pressed glass, such as lacy glass, tree-of-life pattern, stippled backgrounds and frosted effects produced from the mould.
Originally a 16th century Venetian technique which spread across Europe and was revived in England in the 19th century, ice or crackle glass is made by immersing the bulb of molten glass momentarily in cold water, and then reheating and blowing the bulb to its final shape. Sometimes the resulting surface cracks are left open, like the blue jug below, which has sharp edges. And sometimes the surface is smoothed over so that the crackle effect is covered like the vase below this jug.
This kind of frosting on glass was produced by rolling the hot glass onto glass frit (glass fragments almost as fine as sand), or by sprinkling the glass frit over the molten glass item.
Some frosted surfaces appear to have been sprayed onto the glass and then fired on, such as the yellow enamel-like frosting on the jug below.
The frosting on the amber goblet below may have been sprayed on; it is difficult to see how the dull background effect could have been acheived via a mould.
One of the simplest forms of frosting on glass is produced by sandblasting. The result is very similar to acid etching; both methods produce a smooth matt surface but the sand blasting can be slightly rougher to the touch. When a piece of glass is sand-blasted a jet of fine sand (or similar hard grit) is forced against the glass which removes the polish from the glass, leaving a dull matt finish. The technique was first patented by Benjamin Tilghman in Philadelphia in 1870. If required, parts of the design may be masked so the piece is only partially frosted, like the dish below, which was made by Bagley in England.
Another method of removing the shine from the surface of glass to produce a matt finish, is to apply an acid etching fluid, usually hydrofluoric acid. This technique also became popular during the 19th century, although it had been known and used occasionally since the 17th century. In the 1930s Carlo Scarpa, working for Venini, developed a method of acid etching called "Corroso" in which the hydrofluoric acid is mixed with sawdust and then applied to the glass, so producing an uneven frosting which is very attractive.
When pressed glass was first introduced in the 19th century it often had to compete with cut crystal glass. But early pressed glass tended to have flaws like tiny bubbles and specs in the glass. "Lacy glass" designs used an all-over frosted background that looked a bit like lace, hence the name. The lid of this little sugar bowl illustrates the pattern of tiny pimples typical of lacy glass.
The spill vase shown below was made in England in the late 19th century and illustrates the way a frosted appearence was produced from a mould.
The technique of producing a frosted appearance using a mould continued into the 20th century, as illustrated by this mid-20th century leaf dish by Bagleys of England. Workers at Bagley reported that they produced this frosted effect by using a hammer and nail to make indentations in the mould.
The little dish below was made in Australia and shows a variation on the same kind of frosting.
There are many variations on moulded frosting effects, two more are shown below. Each one is produced by contact with a roughened surface on the mould.
There is a frosting pattern known as "tree of life" which was used by Hobbs Brockunier and Co for a series of pressed glass bowls and table accessories first introduced in 1879. Similar frosting has been used by many companies since that time. This little dish, below, is a contemporary example.
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