Slag glass bugle by Davidson's
above: slag glass
bugle attributed to
Davidson's, UK 1890's

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Slag glass

Slag Glass

from the Glass Encyclopedia

Slag Glass: A short explanation

"Slag glass" is a collectors' name for opaque pressed glass with coloured streaks, usually white and/or cream streaks like this brown bugle made by George Davidson's in the North East of England in the 1890's. The name derives from the belief that these colours were achieved by adding slag from iron smelting works to the glass.

The chemical obtained from iron works was pulverised silicate slag acquired by skimming the surface of molten iron during processing and pulverising it after it cooled. But using slag in this way was not the only method of making what we now call slag glass. Harry Northwood and Thomas Dugan made what was called "mosaic glass" when they took over the former Hobbs Bruckenier glassworks in Wheeling, USA around 1902. Challinor Taylor's glassworks in Pittsburgh also made "mosaic glass" and were probably the leaders in manufacturing slag glass in the States in the late 19th century. Mosaic glass was made by combining together glass from two separate pots, one purple and one opal or white. Northwood in particular had problems with breakages and gave up making slag glass after a few years.

When they were produced in the 19th century, slag glass items were called by names such as "Marble glass" or "Brown malachite" "Brown marble vitro-porcelein" "variegated glass" or "mosaic glass".

Slag glass is commonly found in purple, less common in blue and brown and green. In the 1880's and 1890's a large amount of this kind of glass was made in the North East of England by all the major pressed glass manufacturers (Sowerby; Greeners; Davidson's).

In the USA slag glass was made in the 19th century by Atterbury & Co., Challinor Taylor & Co., and H. Northwood Glass Co. In more recent years it was made by Imperial Glass, by Westmoreland Glass, by Akro Agate, and several other companies. It is still popular today, and is made by US glassworks such as Boyd Glass, Summit, and Mosser, who each make a range of slag glass items in a wide range of colours including red and orange.

In the US there was a mold-making company, Washington Beck, whose iron foundry was in Pittsburgh from 1859 until the 1880s. This company made molds for Sowerby in the UK as well as Atterbury and others such as Challinor in the US. This is probably why items in slag glass with a Sowerby makers mark are sometimes mirrored in very similar US production items from this early period.
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Here are some books that include slag glass. Click on any book cover or title to read more about that book.

Imperial Milk Glass 2007 Slag and Marble Glass 2007 American Slag Glass 1997 British Glass 1800-1914 Molten Salts Slags and Glasses 2006

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