American Purple Slag Glass
Written by Patricia McCulley
Purple slag came to the United States from England in the 1880s, probably brought by immigrant glassmen or by Americans returning home from apprenticing there.  This variegated glass was as popular here as with the English, coming at a time when the demand for decorative colored glass was high.  Slagware appealed aesthetically and was affordable.  Production here spanned the years from the mid-1800s to about 1907.  Today, this richly colored glass and its English counterparts are eagerly sought by collectors all over the country.
Acanthus Bowl, Atterbury
Jewel celery, Atterbury
Belknap identified three kinds of slag glass: the open-mix with colors distinctly separate; the fused-mix where they are well blended with no great splotches of either color; and the over-mix characterized by shades of purple with little white.  The three largest American producers of slag glass were the Atterbury & Co., Challinor, Taylor & Co. and the H. Northwood Glass Co.
The Atterbury "White House Factory," so called because of its large output of quality "opal ware," was founded in Pittsburgh in 1859 and closed in 1894.  In addition to opal (milk glass), Atterbury was acclaimed for its lamps, shades and chimneys which won an award at the 1876 Centennial Exhibition.  The company also was highly regarded for the fine quality of its tableware and the wide variety of ware it made in opaque glass of blue, green, lavender and marbled colors.  Much Atterbury slag glass, incorrectly attributed in the past, is being recognized as more information comes to light.
Notched platter, Raindrop, Atterbury
Dart Dar high standard compote, Atterbury
Identification of purple slag here must be made by pattern or catalog picture since it was not originally marked.  Molds for many slag pieces were also used in production of milk glass and some were also used for clear and/or colored pressed glass.  Atterbury's Sunflower, for instance, is found in purple slag, and also in clear, opalescent, amber and blue.  In their 1881 catalog the design was called Lily.
Other identified Atterbury patterns include Raindrop, Dart Bar, Basketweave, the Jewel celery and an Acanthus bowl that Ferson calls part of the Melon with Net pattern group.
Maude S. Butter dish.  Lee says this was the famous Queen of the Turf trotting horse.  Item she pictures was made by Ripley & Co., Pittsburgh, during the 1880s.
Creamer, Sunflower, Atterbury
David Challinor began operations in Pittsburgh in 1864 and some 20 years later moved to a site in Tarentum along the Allegheny.  At that time he took a partner, David Taylor, whose interest was strictly financial.  In 1891, Challinor, Taylor and Co., operating as the Standard Glass Works, became part of the U.S. Glass Co. combine.  Shortly after, the plant was completely destroyed by fire and was not rebuilt.
David Challinor used the term "Mosaic" for his slag glass, as did Northwood.  To further confuse the names, some Challinor ads refer to it as "Variegated Glassware."  Challinor was critical of the term "slag" because of its association with the refuse from iron smelting.  He insisted that this glass was the product of a well conceived and carefully mixed formula.  In fact, the only patent Challinor obtained, in 1886, was for the manufacture of mosaic glass.
His technique was to prepare separate pots of opal and amethyst, heat each to the correct temperature, then mix the two together by careful stirring.  The pot was reheated to just the proper temperature and consistency.  Only then could the men begin to work with it.
Challinor Taylor was the acknowledged leader in the making of slag glass.  The consistently high quality of their glass is testimony to the care with which it was made.  Challinor designs on record include Oval Sett or Oval Medallion, Fan and Star, Flute or Majestic Crown, Dewdrop and Zigzag, Flower and Panel and Mitered Dewdrop.
Open work fruit bowl, Basketweave base, Challinor
Open work plate, Raindrop center, Challinor
The Northwood Co. operated in Ohio and Pennsylvania from 1888 - 1899 when it joined the National Glass Co. combine.  In 1902, Harry Northwood redesigned and, with Thomas Dugan, bought the old Hobbs Brockunier plant in Wheeling which had stood empty since Hobbs closed in 1893.  Almost immediately production of mosaic glass began.  
Mosaic was never an easy glass to work.  Breakage was high.  Frequently there was difficulty in getting the two colors to adhere.  Often one finds a fracture where the two colors have separated.  This might happen if the two colors did not cool at the same rate.
Northwood always had problems with its mosaic glass.  At one point there was so much breakage that heated meetings were held with the union to determine who would be responsible for the cost.  The difficulty was possibly with the procedure used.  Either opal or clam-broth, a translucent grayish glass, in the form of cold cullet was added to the pot of amethyst.  This sounds almost casual when compared to the precise attention Challinor lavished on all aspects of purple slag production, but it does explain the translucence of much Northwood slag, when slag is considered an opaque glass.  The translucent pieces probably made from the amethyst and clambroth mix.
Researchers have suggested that Northwood's output was limited to a few months because of the production problems.  A 1903 Butler Brothers catalog shows an assortment of this ware.
Flute or Majestic Crown covered compote, Challinor
High standard cake plate, #900 in Challinor catalog
The diligent collector may find Northwood mosaic in Beads and Bark, Ocean Shell, Maple Leaf Chalice, Scroll with Acanthus (originally made by the Central Glass Co. in clear glass), Spool, Spool of Thread, Grapevine Cluster and Floralore.  A jack-in-the-pulpit vase was also made.
Other companies also made purple slag glass.  The Canton Glass Co. in Ohio made Primrose in the 1880s.  Barbells was offered by the Jefferson Glass Co, in West Virginia, around 1905.  Belknap pictures a Black Daisy pitcher as an American piece.  I have not been able to find this listed anywhere else.
To complicate further the matter of attribution, molds were sold or traded or just left behind.  When Northwood moved into the old Hobbs building, evidently at least two molds were found in good condition and put to use.  A Hobbs No. 101 match safe surfaces occasionally in Northwood's mosaic glass, as does a sugar sifter in No. 311 which Heacock attributes to Northwood.  Hobbs did not make purple slag.
The vase or toothpick or match-holder that Heacock named Pegleg can safely be attributed to Sowerby, by virtue of marked pieces, and to Challinor.  Lucas reports that identical pieces are still owned by the families of workers who brought them home from the Challinor plant.  There are very minor differences indicating very similar molds.  There is a slight difference in height, and in the Sowerby version the corner pegs are the same size at the top, while in the Challinor pieces, the peg above the body of the piece is narrower.
Floralore crimped bowl, in 1903 Butler Bros. catalog, Northwood
Jelly compote, Spool pattern, Northwood
Originally the glass houses made their own molds.  As factories became busier and molds more expensive they were often acquired from mold makers.  Washington Beck, who had a foundry in Pittsburgh from 1859 into the 1880s, worked closely with both Atterbury and Sowerby.  Considering location, he probably also had Challinor as a customer and no doubt sold molds to anyone who was interested
Challinor's Boot with Spur and the English Jockey's Boot are identical, indicating molds from the same source.  Beck patented just such a glass boot design in 1976.  It was not just workers and techniques that crossed the ocean; molds and designs traveled too.  Lattice edge plates and high standard compotes have been attributed to both Atterbury and Challinor since catalogs for each picture nearly identical items.
It should also be noted that purple slag glass has been produced in more recent times.  In the late 1940, the Fenton Art Glass Co. made plates and animal dishes for L.G. Wright in this color.  In the 1960s the Imperial Glass Corp. made a considerable amount of slag in ruby, caramel and purple.  Westmoreland made what they called purple and green marble glass beginning in 1972.  No doubt, other companies made this glass as well.  Unfortunately for collectors, newer pieces can sometimes be mistaken for older wares.
I should be interested to hear from anyone who has comments, additions, or corrections to add to this overview of the purple slag picture.  And my deep gratitude goes to collectors Elizabeth Banse, Verda Easter, and E.J. Willingford, Sr., for their generosity in sharing photographs of some of their treasures.  Thanks also to Gay LeClaire Taylor of the Museum of American Glass at Wheaton Village for providing information.
Patricia McCulley is an antiques dealer, avid collector and retired library director.  She can be reached at or (856)451-7919.