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Slag glass was a popular material for decorative items from the late 19th to the early 20th century. Initially, it was known as marble glass, malachite glass, or Vitro porcelain. Eventually, it became known as slagware or slag glass. While collectible, the price range varies greatly depending on the item and manufacturer. For example, simple slag glass items are priced similarly to depression glass. This guide will explain how slag glass was made, when it was popular, and what its worth.
What is Slag Glass?
Slag glass is a man-made opaque base glass with marbelized swirls in a different color. Manufacturers used the glass in molds to make bowls, compotes, vases, plant cache pots, and more. In addition, slag glass panels were used in lamps, jewelry boxes, and other collectibles. Slag glass is named after silicate slag, a colorful material that is a byproduct of molten steel. Manufacturers usually make slag glass by mixing this silicate slag with clear glass.
Pettingell-Andrews Company, c. 1910
Gas and Electric Lamps
Welsbach Company, c. 1910
The most common base colors include white, cream, primrose, and blue. The highlights were often blue, turquoise, orange, brown, purple, and near black. Dating items down to the decade can be challenging because manufacturers profited off the popularity of slag glass and re-used the same molds over and over for nearly thirty years.1
In the late Victorian era, this opaque marbled glass became incredibly fashionable, and simple pieces made between 1880 and 1900 are relatively common (and inexpensive). However, the popularity waned at times. Discerning Victorian consumers resisted purchasing marbleized glass in some cases and preferred more decorative elements in crystal. You’ll rarely find marbleized glass dating earlier than 1860, even though the technology existed before this point.2
Is Slag Glass Natural?
Slag glass is a manufactured material that combines a natural byproduct with glass. Manufacturers experimented with different methods to achieve this malachite-like look. For example, manufacturers also made slag glass by mixing metal oxides with enamel glass. The result is a material that lies somewhere between porcelain and glass.
Remember, the most common way to make slag glass was by skimming silicate material from the top of molten iron. According to Norman Webber, some companies referred to slagware as ‘end of the day wear’ because glassmakers collected slag from the surface of iron right before they poured it at the end of the day. “There is another theory that slagware, and some other glass decorated with multi-colored enamels, were made up from odds-and-ends of glass left over at the end of the day,” Webber reiterates.3
What is Slag Glass Worth?
The value of slag glass antiques ranges from $20 – $20,000. Unsigned decorative glass items like compotes and vases tend to sell between $5 – $50, even if they are from the 19th century. Slag glass antique lamps sell between $200 and $2,000, and most of the value is in the light itself. Prices go up significantly if a light is signed by a prominent manufacturer like Tiffany Studios or, to a lesser extent, Bradley & Hubbard.
The chart below highlights some recently sold slag glass items. For example, simple things like a bowl sold for around $20 apiece. On the other hand, Tiffany Studios‘ decorative items sold for several thousand dollars. Finally, a Bradley & Hubbard slag glass lamp sold for $584, typical for that style and age of light.
|Tiffany Studios Picture Frame||$5,000||5/19/2018||Rago Auctions|
|Covered Candy Dish||$150||4/19/2022||eBay|
|Arts & Crafts Hanging Lamp||$275||6/23/2012||Cottone Auctions|
|Victorian Fan Vases, Lot of 2||$40||11/6/2018||Live Auctioneers|
|Tiffany Studios Glove Box||$1,875||11/12/2020||Doyle Auction Houses|
|Bradley & Hubbard Table Lamp||$584||9/17/2016||Cowan’s Auctions|
|Vases, Compote, Creamer, and Bowls, Lot of 7||$129||1/30/2010||Jeffery S. Evans & Associates|
Signed slag glass tends to be worth more than unmarked slag glass. So keep your eye out for glass made by these companies from the 19th century.
- Atterbury & Co
- Challinor, Taylor & Co
- Greener & Co
Companies continued to make slag glass items well into the mid-20th century. Some later manufacturers include Boyd, Imperial, and Westmoreland.
- Davis, Derek, and Middleman. Colored Glass or Coloured Glass. Clarkson N. Potter, 1968.
- Notley, Raymond. Popular Glass of the 19th and 20th Centuries: A Collector’s Guide (Miller’s Collector’s Guides). Miller/Mitchell Beazley, 2000.
- Webber, Norman. Collecting Glass. Arco Publishing Company, 1973.