Slag glass is a type of colored pressed opaque glass made using the "slag" left over during the iron smelting process. It is also known as malachite glass, marble glass, mosaic glass, and variegated glass. The glass is created by using pulverized silicate slag, an ingredient that forms on the top of molten iron as it cools down. Slag glass was originally created in the United Kingdom in the 1890s by adding this slag substance during the glass-making process. The visual marbling of slag glass is reminiscent of slag, which is the byproduct of steel production. Slag glass was a sought-after material for decorative items from the late 19th to the early 20th century. Manufacturers used the glass in molds to make bowls, compotes, vases, plant cache pots, and more. Slag glass panels were also used in lamps, jewelry boxes, and other collectibles. The price range of slag glass varies greatly depending on the item and manufacturer.