Slag Glass Identification and Valuation

Slag glass is a type of pressed glass that is known for its brilliant and vibrant colors. These colors are created through different repurposing techniques. Learning how to identify and value this glass can help if you are looking to collect or just learn more about this interesting glassware.

When identifying slag glass, look for a marbling effect. True slag glass is marbled and has a variety of bright colors. The value of slag glass is determined by the rarity of the item and the color. Depending on the rarity of the item, slag glass is worth anywhere from $50 to $1500.

Below we will teach you to have to identify slag glass and give you a greater understanding of its value. Slag glass has a rich history that makes it extremely valuable to collectors.

Antique Sowerby Purple Malachite Slag Glass Spill VASE 1880s
Antique Sowerby Purple Malachite Slag Glass Spill VASE 1880s – $65 – from PassedPossessions on Etsy

Characteristics of Slag Glass

Slag glass gets its name from slag. Slag is the byproduct of steel production. When iron-ore is smelting during steel production, the remaining residue is a glass-like, glossy material. This material takes on different colors depending on the minerals and elements that are present in the iron. This leads to marbling in the colors of the glass. This marbling is one of the best ways to identify slag glass.

When identifying authentic slag glass, pay close attention to the marbling. It should not have white streaks mixed into the color, nor should it be one solid color. The marbling should be a creamy white color that is evenly mixed into the base color. The marbling is sometimes compared to tortoiseshell.

1960's Imperial Slag Glass Cruet Collection Amethyst, Green, and Chocolate
1960’s Imperial Slag Glass Cruet Collection Amethyst, Green, and Chocolate – $185 –from HowOriginalStore on Etsy

The colors of slag glass are also a great way to identify authenticity. Most antique slag items are brown, blue, green, or purple. Purple is the most common slag glass color. Brown malachite slag glass pieces are the rarest and most coveted colors of slag glass. Real slag glass will not have a solid color but rather a blended, marble look.

Value of Slag Glass

The worth and value of slag glass varies. A piece of slag glass will be worth more if it is a rare color or a rare item. Slag Glass prices range from 50 dollars to 1500 dollars. Slag glass lamps are one of the most sought-after items made of slag glass. These lamps rarely sell for less than 100 dollars. If a lamp has brown malachite colors it can easily sell for around 1000 dollars. This is due to the rarity of the color. (Source)

Antique Art Nouveau Green Slag Glass Table Lamp
Antique Art Nouveau Green Slag Glass Table Lamp – $1,000 from ScrantonAntique on Etsy
Vintage Metal and Red Slag Glass Table Lamp
Vintage Metal and Red Slag Glass Table Lamp – $259 from MoFabFinds on Etsy

The value of slag glass items can also be determined by the condition of the item. If the item is in good condition, with no cracks, discoloration, or signs of neglect, it will be worth more.

Vintage Imperial Caramel Slag Glass Octagonal Covered Candy Dish – Sold for $178.49 from kbt..llllll on Ebay

The older piece, the greater value it has. Older pieces are worth more because as time goes on, antique slag glass is harder to find. It is hard to keep fragile glass intact for decades. You can determine the age of a piece of slag by finding the date of production. This is listed on the bottom of most slag glass items, especially lamps.

How to Tell if Slag Glass is Real

For today’s collectors, slag glass is a greatly sought-after item that can go for a lot of money. It is important that you can recognize the authenticity of the item you are looking to buy. This will ensure that the money you are spending is worth it. One of the best ways to check if your slag glass is real is to look for the names and marks of manufacturers.

Fenton Art Glass Purple Slag Peacock Vase - Marked
Fenton Art Glass Purple Slag Peacock Vase – Marked – Sold for $179.99 from hannahs_corner on Ebay

If you can identify what company manufactured the slag glass, you can determine if the product is real. Slag glass producers mark their products with the company’s initials or the company’s logo. This mark is usually made at the bottom of the lamp. Some well-known slag glass manufacturers include Sowerby, Davidson, and Greeners. These three manufacturers are very well known in the United Kingdom.

Atterbury & Company, Challinor Taylor & Company, and H. Northwood Glass Company are some well-known manufacturers from the United States. These are just a few of the companies that produce authentic slag glass. When looking to purchase real slag glass, look for the marks of the manufacturer. Once you find those marks, research the company to see if they are an authentic brand. If the item does not have any names or marks, the piece likely is a fake.

Real slag will always have a creamy marble effect. The marble should never be streaky and it should blend well with the color of the glass. Real slag glassware will also never just be one solid color, it will always be blended.

History of Slag Glass

Production of slag glass originated in late 19th century England. Glass manufacturers were thought to have added slag from iron smelting to molten glass. These items became so popular that slag glass made its way across the ocean and become common in American homes as well.

Challinor Taylor & Co. was one of the most prominent American Slag glass manufacturers. Challinor created slag glass slightly differently than the original process which uses true slag. Challinor would instead combine two colors of molten glass. This would still give the marble effect without the use of actual slag. (Source)

Challinor Taylor Slag Glass Salt Shakers
Challinor Taylor Slag Glass Salt Shakers from diggerdaveb on Ebay

This created the marbled effect and bright variations in color that make slag glass so unique. Slag glass was extremely popular when used to create lampshades. Most homes in the late 19th century and even some older homes today could be found using a slag glass lampshade as decor. They are a great way to add color to any room.

Slag glass is no longer produced as it once was. Most companies have halted the production of slag glass items altogether. This is a big part of why slag glass is so valued today. Despite its rarity, you can still find slag glass items in modern homes. They bring a sense of the past into a home and they add a pop of color. Mixing antique pieces with modern amenities is a popular decorating technique.

2 Fenton Slag Glass Cats – Sold for $400 from termel-8977 on Ebay

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