What exactly is slag glass?

Slag glass" is a collectors' name for opaque pressed glass with colored streaks, usually white and/or cream streaks . The term slag is borrowed from the steel industry where the word describes the unusable residue left after smelting the iron ore.

Is slag glass worth anything?

American slag glass makers included Westmoreland Glass, Boyd Glass, Imperial Glass, among others. Slag glass comes in many colors such as chocolate or caramel, purple, blue, pink, and red. Values for slag glass, particularly, kitchenwares and lampshades command values from $50 to $1500 with collectors .

Is slag glass harmful?

" Slag generated from the EAF process can contain toxic metals, which can be hazardous to human and environmental health ".

What is another word for slag glass?

Adding to the beauty of slag glass – also known as malachite glass, marble glass, and mosaic glass – is its rich history that reflects the ingenuity of turn-of-the-century glassmakers.

Is slag good for anything?

Although the construction industry does use some slag as an aggregate, most is simply discarded. However, slag could be used to treat acid soils or acid mine drainage . Doing so would both offset the cost of restoring abandoned mine areas, as well as decrease steel manufacturers' current waste footprint.

Is slag glass still made?

By far the most common colour for slag glass was purple, but it was also made in blue, turquoise, green, and brown glass. Modern slag glass is still being made today in USA , and comes in a variety of colours.

Does slag have any value?

But slag itself has value, and technologies have emerged to recycle and reuse reprocessed, granulated slag in different building materials, such as cement, brick, concrete aggregates, wall materials, and glass-ceramic tiles.

What are the disadvantages of slag?

However, there are also disadvantages to using slag as a cement additive. It can decrease the compressive strength of concrete samples and lead to a greater decrease in strength after frost resistance testing .

Did Tiffany use slag glass?

From the late 1890s through the 1920s, Tiffany Studios produced mosaic glass shades (some of which are classified as slag glass), that featured geometric and floral motifs.

Why is it called slag?

Outside of slang, slag refers to residue from the process of smelting, a method used to separate a metal from raw ore. This slag comes from a German root and has been recorded in English since the 1550s. The British slang slag, for a “worthless or objectionable person,” is seen by the late 1700s.

What color is slag glass?

According to the online Glass Encyclopedia (glassencyclopedia.com), slag glass is most commonly found in purple and less often in blue, green, and brown (AKA caramel) .

What is the difference between slag glass and stained glass?

Slag glass, which is the correct name of this early style of lampshade, looks different from stained glass. Stained glass is either opaquely, uniformly colored, OR, the color is streaked with white. Slag glass looks like marble, uneven and swirly .

What is the purpose of slag?

Slag floats on the surface of the molten metal, protecting it from oxidation by the atmosphere and keeping it clean . Slag forms a coarse aggregate used in certain concretes; it is used as a road material and ballast and as a source of available phosphate fertilizer.

Is slag safe to touch?

Blast furnace slag granules or granulated slag may contain 'glassy wool' or microscopic sharp glassy material, resulting from the rapid quenching of molten slag. Skin and eye protection should be worn to protect against exposure and mechanical abrasion.

What Is Slag Glass? (2024)

The first pressed glass pieces that collectors refer to as "slag glass" were made in the 1890s, using the glass-like by-product of iron ore known as—you guessed it—slag. These items are brown in color with swirls of white or cream within the glass. Other types of metal ores produce different colors of slag when they are refined.

History

Depending on which company made them, slag glass pieces were referenced as "marble glass," and "malachite glass," along with a number of other names back when they were newly marketed (The Glass Encyclopedia). Slag glass was often used in lampshade production as well as for crafting many different types of decorative objects.

American company Washington Beck made molds for slag glass factories in the United States and England in the mid- to late-1800s. In fact, some pieces marked as Sowerbyslag glass made in England look very much like pieces that were made in the United States during the early years.

Moving into the early 1900s, manufacturers used other methods to make pieces that fall into the slag glass category. "Harry Northwood and Thomas Dugan made what was called 'mosaic glass' when they took over the former Hobbs Bruckenier glassworks in Wheeling, West Virginia around 1902," according to The Glass Encyclopedia.

Challinor, Taylor, and Co. also made their own version of this type of glass around the same time. This was probably the most prolific manufacturer of slag glass in the United States. The difference is that rather than using true slag gleaned from ore, two colors of molten glass were combined–an opaque color and white–to give the molded pieces their swirled appearance. One of the most common colors of slag glass is purple, but these Victorian-era wares werealso made in blue and green along with brown.

Identification

Recognizing slag glass is easy due to the distinctive coloration. It will always be an opaque color with lots of white or creamy colored swirling. Figuring out who made a piece, and how old it is, can be a bit more tricky.

Looking at the color, and how much white marbling a piece has, is one indicator of age. Older pieces will be heavily marbled and quite chunky. Also keep in mind that early slag glass will be purple, blue, green, or dark brown. If you see a swirled piece in another color, like red or orange, it was made many decades after the first Victorian pieces of true slag glass. That doesn't mean it isn't valued by collectors, however.

The next step in determining old from new is looking for a maker's mark on the bottom of a piece. Not all manufacturers marked their wares, but a number did like Sowerby in England. Akro Agate is an American company that marked most of their wares ranging from children's dishes to small decorative flower pots. Newer glass by Fenton, Boyd, and Mosser may also be marked.

Valuation

Some of the most costly slag glass pieces take the form of lampshades by well-known makers like Handel, Bradley Hubbard, and Tiffany. These easily sell for thousands when in excellent condition, with Tiffany being the top of the line, of course. Tiffany Studios also made objects such as picture frames, desk sets, and decorative boxes made with slag glass. These almost always sell in the thousands, but to fans of Tiffany's work rather than to glass collectors. Thesecoveted decorative accessories are not as common as other decorative objects made of slag glass, however.

Fun Fact

Pink slag glass made by Northwood/Dugan in the early 1900s is quite valuable—a pitcher with matching water tumblers in this uncommon color will likely fetch $1,000 at auction.

Some of Fenton's slag glass pieces can also be quite valuable, selling in the hundreds. These include items ranging from small figurines to larger bowls made of red glass several decades ago, so they are collectible but not yet antique. Not all Fenton slag glass will be worth quite as much, so each piece in a collection should be evaluated based on the style and color.

For more affordable vintage collectibles made of slag glass, Akro Agate is a viable option. Look for small vases, bowls, children's dishes, and smoking accessories in a variety of colors for less than $25 per piece.

What Is Slag Glass? (2024)

History

Identification

Valuation

Fun Fact

FAQs

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