Hold a piece of slag glass up to the light and you'll see it: swirls of color moving through milky white like clouds, marble or agate. No two pieces swirl quite the same way, which is exactly why collectors love it.
Our Imperial Glass green jade slag owl is in the shop now for $45, and it's the only one we have.
See the slag glass owl →
Where the name comes from
In the late 1800s, English glassmakers found that mixing slag, the leftover waste from iron smelting, into their glass made beautiful streaked, opaque colors. The name stuck long after the iron slag itself stopped being used. Today, "slag glass" means any opaque glass with two or more colors swirled through it, usually a color marbled with milky white.
The main eras
- Victorian (1880s–1900): English makers like Sowerby and Davidson produced purple-and-white "malachite" and "vitro-porcelain" pieces, often marked with a peacock-head or lion emblem.
- Early 1900s: Slag glass panels glowed in Arts and Crafts and Tiffany-style lamp shades.
- 1950s–1970s: American companies revived it in a big way. Imperial Glass of Bellaire, Ohio, is the name most collectors know, with caramel slag, purple slag, green jade slag and red slag in animal jars, compotes and figurines. Westmoreland, Fenton and Boyd also made slag pieces.
Imperial Glass colors to know
- Caramel slag ("Chocolate"): brown and tan swirled with cream, the most common.
- Purple slag: deep violet marbled with white.
- Green jade slag: teal, green and blue swirled with milky white, harder to find and usually worth noticeably more than caramel.
- Red slag: red-orange swirls, made in smaller runs.
See it in person: slag glass in the shop
Green jade slag and red slag, one to display and one to wear. Each one is a single piece, so when it's gone, it's gone.
How to tell what you have
- Look for marks. Imperial used an "IG" mark (an I over a G), later "LIG" or "ALIG" after the company changed hands. Marks are usually on the base, so lids and loose parts are often unmarked.
- Hold it to the light. Real slag glass is opaque or nearly so, with swirls running through the body of the glass, not painted on the surface.
- Check for wear. Look for gentle wear on the base and any rims, and run a finger along the edges for chips and flea bites.
- Watch for reproductions. Some molds were reused by later makers, so a mark matters more than the shape alone.
Caring for slag glass
Wash by hand in lukewarm water with mild soap, never in the dishwasher, and avoid sudden temperature changes. Display it out of harsh direct sun.
Slag glass in the shop
- Imperial Glass green jade slag owl jar lid with amber glass eyes, a striking swirl of teal, green and white that's lovely on its own or as a replacement head for an owl jar.
- Red slag and carnival glass bead necklace with real pearls, a 1940s strand you can wear.
Keep browsing:
Collectable glass →Vintage necklaces →Vintage home decor →
Keep reading: What Is Milk Glass? · What Is Carnival Glass? · What Is Sommerso Glass?
Do you have a slag glass piece that came from someone you love? We'd love to hear which color it was.
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