page_title: Slag
section_title: Ancient uses
hierarchical_section_title: Slag / Ancient uses
caption_attribution_description: English: A 200 kg lump of slag from iron ore melting. It was found near Snorup in western Jutland, Denmark. It's estimated that it's from around 200-500 AD.
context_page_description: Slag is the glass-like by-product left over after a desired metal has been separated from its raw ore. Slag is usually a mixture of metal oxides and silicon dioxide. However, slags can contain metal sulfides and elemental metals. While slags are generally used to remove waste in metal smelting, they can also serve other purposes, such as assisting in the temperature control of the smelting, and minimizing any re-oxidation of the final liquid metal product before the molten metal is removed from the furnace and used to make solid metal. In some smelting processes, such as ilmenite smelting to produce titanium dioxide, the slag is the valuable product instead of the metal.
context_section_description: During the Bronze Age of the Mediterranean there were a vast number of differential metallurgical processes in use. A slag by-product of such workings was a colorful, glassy, vitreous material found on the surfaces of slag from ancient copper foundries. It was primarily blue or green and was formerly chipped away and melted down to make glassware products and jewelry. It was also ground into powder to add to glazes for use in ceramics. Some of the earliest such uses for the by-products of slag have been found in ancient Egypt.
  Historically, the re-smelting of iron ore slag was common practice, as improved smelting techniques permitted greater iron yields—in some cases exceeding that which was originally achieved. During the early 20th century, iron ore slag was also ground to a powder and used to make agate glass, also known as slag glass.
caption: Early slag from Denmark, c. 200-500 CE
exif: {}