Slag glass, also known as marble glass or malachite, is a type of opaque, streaked pressed glass. Production of slag glass originated in late-19th-century England, where glass manufacturers are thought to have added slag from iron-smelting works to molten glass to create a range of effects—from tortoiseshell to marbling. Among other uses, slag glass was a popular material for lampshades.

One of the first glass foundries to produce slag glass (although it was not called that at the time) was the Gateshead, England, firm of Sowerby, which patented its recipe for purple malachite glass in 1878. Sold into the U.S. market as "blackberries and cream," this popular formula was followed by other malachite colors, including a lemon-yellow called Giallo, a drab green called Pomona, a blue malachite called Sorbini, and Sowerby’s famous Brown, which is very difficult to find today.

Since the process of making slag glass was shrouded in a certain amount of mystery, stories sprang up to try and account for the process behind the effects. For example, it was a good bet that Sowerby’s Blue Nugget color of 1883 was the result of adding cadmium to molten glass, but how to explain Gold Nugget? Stories soon spread that John George Sowerby, son of the company’s founder, was tossing gold sovereigns into batches of amber glass to create this dramatic hue.

In the United States, manufacturers such as Westmoreland and Akro Agate picked up on the techniques developed in England and produced their own versions of slag glass. As in England, one of the most popular applications for their pressed opaque glass was in lampshades. Wide bands of creamy colors allowed the light source in a lamp to fill a room with a soft ivory glow, while the purples and greens and reds pieced together in detailed leaded shades resulted in multi-colored illumination.

Just about anyone who was making lamps during the Art Nouveau period, from Tiffany to Roycroft to Steuben, might have used slag glass in their shades. But whether they did or not in a particular lamp is another matter. The problem is that today, "slag glass" is used rather casually by dealers and collectors alike to refer to almost any type of pressed opaque glass containing colored swirls or streaks. The key to determining if a piece of glass is "true" slag or just a handsome example of pressed glass is to look for glass that is obviously and richly marbled rather than simply colored or streaked.

Best of the Web (“Hall of Fame”)

The Lampworks

The Lampworks

Lamp collector and dealer Dan Edminster has put together an incredible reference site on antique lamps and related … [read review or visit site]

Texans Incorporated: The History of a Lamp Company

Texans Incorporated: The History of a Lamp Company

Mark Stevens has created an impressive living memorial to Texans Inc., a 20th century Texas manufacturer of ceramic… [read review or visit site]

The Lamps of H. G. McFaddin

The Lamps of H. G. McFaddin

Bruce Bleier's tribute to the Emeralite and Bellova lampshades made from Czech glass and popularized and distribute… [read review or visit site]

Fairy Lamp Club

Fairy Lamp Club

This incredible site is a stunning showcase for Victorian and contemporary fairy lamps, a style of lamp with a glas… [read review or visit site]

Gas Pressure Lanterns, Lamps and Stoves

Gas Pressure Lanterns, Lamps and Stoves

Terry Marsh’s beautiful showcase of gas-pressure lanterns, lamps, stoves, irons, and heaters from the 1920s o… [read review or visit site]

Clubs & Associations

Other Great Reference Sites

Most watched eBay auctions    

Antique**exquisite**arts & Crafts Green Slag Glass Table LampBradley & Hubbard Handel Style Bronze Metal Ovelay Slag Glass Lamp Shade NrOld Brass Iron Lamp Base For Arts & Crafts Slag Glass Shade Bradley Hubbard #189Art Nouveau/arts&crafts Era Whalley Leaded Stained Slag Glass Lamp Shade,c.1910Antique Arts & Crafts Unique Leaded Slag Glass Lamp Handel Duffner Kimberly EraArt Nouveau Signed"royal Art Glass Co." Seashell Two Tone Slag Glass Lamp,c.1910Antique 1910 Era Large Bradley & Hubbard Ceiling Fixture Panel Slag Glass LampAntique Dual Pull-chain Socket Slag Glass Lamp Base Old Brass Iron Lamp Base For Arts & Crafts Slag Glass Shade Bradley Hubbard #228Large Carmel Slag Glass Table Lamp With Light Lit Up Base As Is 18" Shade NrArt Nouveau/arts&crafts Era Whalley Leaded Stained Slag Glass Lamp Base,c.1910Vintage 6-panel Slag Glass Art Deco Lamp ShadeAntique Slag Glass Lamp Shade For Banquet LampFine Antique Miller Table 2 Lamp Slag Stained Glass Base Art Deco Nouveau 1907Antique Designer Bournique Kokomo Opalescent Slag Glass Art Deco Lamp ShadeAntique Bronze Articulated Desk Lamp With Slag Glass Shade-arts & Crafts-missionArts & Crafts Mission Tiffany Style Leaded Stained Glass Lamp Slag Glass PolygonAntique Vintage White Pink Slag Glass Chandelier Ceiling Light Fixture LampVintage Lamp Base Slag Glass Akro AgateVtg Deco Agate Slag Glass Lamp/smoking Stand/ashtray Spacer Lamp Repair Parts Vintage Lead Slag Glass Lamp Shades Brown White SwirlVintage 10" Art Deco Slag Glass Table/dresser Lamp ~ Houzex ~Vintage Art Deco Slag Glass Style Lamp ShadeVintage Small Tree Trunk Lamp Base Slag / Stained Glass Type Tiffany StyleVintage Tiffany Slag Lamp Shade / Copper Frame / Brown Glass / Gorgeous PieceAntique 1920's Art Deco Era Houze Houzex Jadeite Jadite Slag Bridge Table LampVintage Old Tiffany Style Blue Slag Stained Glass Light Hanging Chandelier Lamp

Recent News: Slag Glass Lamps

Source: Google News

The Strange Blowpipe 19th Century Miners Used to Analyze Ore
Wired, August 19th

At that point, some of the lead would oxidize and react with any silicates in the ore to produce a glass-like substance called slag, and the rest of the lead would form an alloy with any gold or silver in the sample. You'd end up with a tiny chunk of...Read more

Maine Antique Digest, August 8th

Betty lamps, Whale oil, Fluids inc. tin & bull's eye & drape patt., Cut glass apothecary jar full of shells made into lamp, Copper milk can lamp, 3 lg. retro. metal bank lights 34” high, Finger lamps inc. blue cut overlay etc., Student's desk oil lamp...Read more

2014 Toyota FJ Cruiser-Last chance to snag this off-road warrior, August 3rd

package ($4,410 by itself) that adds features such as front and rear Bilstein shocks, roof rack, privacy glass, cruise control, floating-ball compass and inclinometer, power mirrors with lamps, and then throwing in 16-inch TRD beadlock look wheels...Read more

Couple returns to antique business
StarPhoenix, August 1st

Orest and Marion are retired from the University of Saskatchewan and decided to begin anew in the antique business with their son and daughter-in-law. Some of the store's specialties include 1920s Slag glass, Tiffany style lamps, retro lamps from the...Read more