Slag Glass: Marbled Pressed Glass of the Victorian Era
Slag glass is a type of pressed glass characterized by its distinctive marbled or streaked appearance, created by mixing opaque white glass with one or more colored glasses during production. First produced in the 1870s-1880s in England and America, slag glass derives its name from its resemblance to the slag byproduct of iron smelting. The most common variety is purple (amethyst) and white, though it was also made in blue, green, red, pink, butterscotch, and caramel tones.
Identification & Makers
English slag glass was produced primarily in the northeast of England by firms including Sowerby (peacock head mark), George Davidson (lion and crown mark), and Greener & Co. (lion with axe mark). American manufacturers include Challinor, Taylor & Co. of Tarentum, Pennsylvania, and Atterbury & Co. of Pittsburgh. Pieces are identified by their distinctive swirled coloring, pressed pattern designs, and sometimes maker's marks molded into the base. The glass has a dense, opaque quality quite different from transparent colored glass.
Types & Styles
Purple Slag: The most common and widely collected variety, ranging from deep violet to lavender marbled with white. Blue Slag: Less common, produced primarily by English makers. Caramel Slag: Made by Indiana Tumbler & Goblet Co. (Greentown, Indiana) around 1900-1903; highly collectible. Red Slag: Quite rare, commands premium prices. Pink Slag: Produced by several makers, the rarest being Inverted Fan & Feather pattern. Common forms include covered dishes (especially animal-shaped), bowls, pitchers, creamers, sugar bowls, and decorative plates.
Auction Price Ranges
| Item | Price Range |
|---|---|
| Purple slag covered animal dish | $40-$200 |
| Purple slag bowl or compote | $30-$120 |
| Caramel slag (Greentown) tumbler | $150-$500 |
| Caramel slag covered butter dish | $400-$1,200 |
| Red slag piece (any form) | $200-$800 |
| Pink slag Inverted Fan & Feather | $300-$2,000 |
| English marked Sowerby piece | $50-$250 |
| Blue slag bowl or plate | $60-$200 |
Condition Factors
Check for chips along mold seams and edges, as these are common in pressed glass. The marbling pattern affects value; pieces with dramatic, well-defined swirling command premiums over muddy or overly uniform examples. Roughness on the base is normal for pressed glass and not a defect. Cracks are deal-breakers. Lids and covers must be original matches. Reproductions exist, particularly of purple slag and caramel slag; newer pieces tend to have less definition in the pattern molding and more uniform coloring.
Collecting Tips
Caramel slag from Greentown, Indiana, is the most actively collected category and commands the highest prices. Purple slag remains affordable and widely available, making it an excellent starting category. Learn to distinguish Victorian-era slag from 1950s-1970s reproductions by Imperial Glass and others; reproductions are often marked "IG" but not always. Collect by form (all covered animal dishes, for example) or by color for a focused collection. English slag glass with maker's marks is underappreciated in the American market and can be acquired reasonably. Always check auction records for comparable pattern and color combinations before purchasing.