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 Vintage Miller Leaded Slag Glass Lamp Shade Bradley Hubbard Multi ColorArts Crafts Sconce Antique Light Slag Glass Bradley Hubbard Handel Era Lamp NrAntique Old J A Whaley Leaded Slag Glass Arts & Crafts Tiffany Era Lamp - NrBradley Hubbard Arts Crafts Slag Glass Reverse Painted Handel Era Antique LampW Large 16" Antique Curved Slag Glass Metal Frame Lamp Shade Classical UrnsLarge Antique Caramel & Green Slag / Stained Glass Lamp Shade 1900s StunningHandel Arts Crafts Leaded Slag Glass Antique Tiffany Bradley Hubbard Era Lamp NrGorgeous C. 1900 Miller Multicolored Slag Glass Lamp 15"Bradley Hubbard Arts Crafts Antique Slag Glass Nouveau Mission Handel Era LampAntique Slag Stained Glass Lamp ShadeWonderful C. 1910 Royal Art Glass Co. Slag Glass Lamp 15"Antique Old Vintage Charles Parker Leaded Slag Glass Panel Lamp - NrA++ Vintage Stained & Slag Glass Peacock Feather Lamp ShadeAntique Slag Stained Glass Lamp Shade***antique Slag Glass Lamp*** A Beauty No Reserve Exceptional 3 Color Bradley & Hubbard Slag Glass LampAntique Vintage Slag Glass Table LampLarge Antique Custard Slag Glass Lamp Shade Gold Filigree Excellent Tulip StyleCould Be Beautiful Table Lamp 4 Restoration Project, Slag & Eisenglass IsinglassAntique Bent Curved Slag Fluted Clear Glass Lamp Shade Parts 7+1 PanelsVintage Lamp Base Slag Stained Glass Tiffany Type ~ Deco, Nouveau, Fleur De LysAntique Art Deco Arabian Desert Camel Metal Filigree Slag Glass Old Boudoir LampMinty Fresh And Fine Bradley & Hubbard Art Nouveau 8 Panel Slag Glass Lamp Antique Large Handel Era Green Opalescent Slag Glass Lamp Lotus ShadeIron And Brass Floor Lamp Slag GlassStained Leaded Slag Glass & Metal Candle Light Desk Table Lamp Jeweled FlowersLarge Lot Of Vintage-hanging /table Oil/electric Lamp Parts-marble-slag GlassVintage Tulip Stained Slag Glass Filigree Ceiling Swag Hang Fixture Light LampRare Antique / Vintage Turquoise Slag Glass Miniature Oil Lamp BaseVtg Blue Stained Slag Glass Tulip Style Hanging Swag Lamp, 18"Vintage Leaded Stained Slag Glass Grey Wh Lamp Shade Hanging Light Chandelier ~Stained Glass Tiffany Style Shade White Slag Glass 10" X 7" For Fan Or Lamp