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    

Bradley Hubbard Arts Crafts Mission Slag Glass Handel Antique Hanging Lamp LightArts&crafts,nouveau,deco Signed Handel "wisteria" Leaded Stained Slag Glass LampHandel Arts Crafts Leaded Reverse Painted Slag Glass Lamp Base Bradley Hubbard Arts&crafts,nouveau Era Tiffany Studios Style Leaded Stained Slag Glass LampHandel Arts Crafts Slag Glass Leaded Overlay Bradley Hubbard Era Lamp Base NrAntique Arts & Crafts Aesthetic Slag Glass & Metal Filigree Old Victorian LampLarge 16 Panel Slag Glass Lamp,handel, Bradley And Hubbard, Miller Era.Wilkinson Leaded Slag Glass Arts Crafts Mission Handel Bradley Hubbard Era Lamp Arts&crafts,nouveau,tiffany, Handel Era Leaded Stained Slag Glass Lamp Shade Nr!Bradley Hubbard Reverse Painted Arts Crafts Slag Glass Handel Era Antique LampAntique Art Deco Era Ruby Red & Cream Colored Slag Glass Parlor Boudoir LampIncredible Gold Miller Bent Panel Slag Glass Lamp Signed N/rBradley Hubbard Arts Crafts Leaded Slag Glass Antique Handel Era Lamp Bradley Hubbard Arts Crafts Leaded Slag Glass Mission Antique Handel Era Lamp NrLot 4 Antique Vtg Lead Metal Slag Glass Lamp Shades Boudoir Deco Nouveau StyleAntique Purple Green Slag Glass Hanging Lamp 6 Bent Curved Panel 14" ShadeAntique Bent Slag Glass W/ Art Nouveau Metal Hanging Ceiling Lamp Light FixtureLarge Elegant Bradley & Hubbard Overlay Slag Glass LampAntique Cast Iron Lamp Finial For Reverse Painted Or Slag Glass Lamp Miller B&hAntique Arts & Crafts Lamp Shade, Green Slag Glass Off A Bradley & HubbardTiffany Style Table Lamp, May Be Miller. Two Ram Heads,two Cherubs Slag StyleVintage Green Slag Glass Tiffany Style LampHeavy 6" Brass/bronze Table Lamp Base For Slag Art Glass Shade-parts Z331Antique Stained Glass Slag Table Lamp W/ Floral Base & Chain Pull. *tiffany Era*Handel Era Lamp Base Saturn Pulls Miller B&h Rainaud For Leaded Slag ShadeWeber Light Socket Cluster Handel Miller B&h Slag Leaded Antique Lamp HubbellAntique Vintage 1920's Electric Cast Metal Blue Slag Table Lamp LightVintage Lavender Lilac Slag Glass Paneled & Brass Lamp Shade Old Antique Arts Crafts Oak Wood Baluster Slag Stained Glass 2 Socket Lamp Base Antique Slag Stained Glass Lamp Shade, Round Ball ShapeVintage Tiffany Style Green Slag Sained Glass Shade Hanging Ceiling Lamp Light Slag Glass Lamp Shade Antique Art Deco 1920's Amber And BeigeBeautiful Art Nouveau Stained Glass Slag Leaded Lamp Shade Round Ornate Vintage / Antique Bridge Arm Lamp Bronzed Gold Slag Glass, Cast Iron Vintage Wrought Iron Slag Glass Lantern Fixture Lamp Chandelier Low ReserveTiffany Style Vintage Stained Slag Glass Pale Pink Lamp Shade Vtg Dark Bronze Lamp Base Slag Glass Art Bradley Hubbard Era Style Tiffany Style

Recent News: Slag Glass Lamps

Source: Google News

Furnishings and Decorative Arts, Asian, Jewelry, Coins and Fashion in Rago's ...
ArtfixDaily, March 26th

Lighting: an English cut glass chandelier, a continental gilt-bronze chandelier, a Charles et Fils table lamp, a pair of gilt-bronze sconces; lamps by Handel, Slag and Bailey Banks & Biddle. Louis XVI and Federal gilt mirrors. Clocks: Louis XV style...Read more

What's it Worth: pottery lamp base, cameo collection, March 14th

I would like to know if it is worth anything before I give it away. — C.H.. ANSWER: This pottery lamp base probably once held a cloth or leaded-glass shade. Unfortunately, the original sockets have been replaced with inexpensive modern sockets, which...Read more

ArtfixDaily, February 24th

Enthusiasm in these categories can be represented by a French cameo glass and bronze table lamp that drew $23,750 against a pre-sale estimate of $1,500/2,500, an Art Nouveau slag glass and gilt bronze chandelier that drew $27,500 against a pre-sale ...Read more

PUBLIC SALES: Feb. 15, 2015
LancasterOnline, February 13th

$1,100; step-back display cabinet, $1,018; Willard-style tall case clock, $990; Hepplewhite bow-front chest, $880; harvest drop-leaf table, $715; corner cupboard, $715; high-wheeled baby coach, $660; slag glass table lamp, $605; Shotwell gas pump...Read more

Arts and Crafts to Modern Masters
Maine Antique Digest, December 30th

It is copper, patinated metal, and leaded slag glass, and has four sockets. A fine pot from Arequipa ... If this two-day sale of early 20th-century decorative art and modern ceramics and glass on Saturday and post-1950s design on Sunday does not bring...Read more

Glass lamp, pickle jar, Victrola and Sitzendorf figurine: Attic Finds
The Plain Dealer -, November 6th

ANSWER: Pittsburgh Lamp, Brass & Glass Co. made your lamp around 1915. The hexagonal, intricately modeled base was used on a variety of styles made by the firm. 1825 is the model number. The marbleized, caramel-colored glass is known as "slag" ...Read more

Auction Watch: Heinz, other collectibles will be on the block
Tribune-Review, November 2nd

A large selection of glass bottles includes locally made vessels from McKees Rocks and other nearby towns. Of special note are milk bottles and other items made exclusively for the Pennsylvania Railroad that featured the rail giant's famous keystone logo...Read more

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

Then you'd combine the ore with some tiny lead pellets in a scorification dish (those are the little clay dishes inside the front part of the case), and heat the whole thing with the alcohol lamp (the silver object in the middle of the case with two...Read more