Red Iron Oxide

How to Make Brown Glass

Hematite is used as an effective glass colourant because of its very high iron content. It is often used in combination with anthracite, which trims redox levels during colouration. It is also used in combination with iron pyrite when the pyrite does not provide sufficient iron levels for the glass melt. This is because Fe2O3 can introduce large amounts of iron without introducing too much sulphide and other unwanted materials that can destabilize the glass.

Studies have proven the important role of sufficient iron levels in glasses coloured amber with carbon. Without sufficient levels of this container glass pigment, the sulphides present would change the colour to black. A. Bork supported these studies with his own brown glass oxide experiments, which showed that sulphide glasses of a faint yellow hue turned brown with the addition of natural red iron oxide at certain levels.

H Weckerle again reinforced these findings by concluding through his own studies of amber glass oxide that the faint amber colour produced by carbon container glass oxide was caused by the iron in the sand, as well as the formation of iron sulphides. Sulphides alone did not produce the desired colour when the raw materials were free of natural red iron oxide, proving that the container glass pigment must contain iron to create a sufficient amber colour.

Today, it is accepted that iron modifies the amber colouration through the formation of simple or complex sulphides. Yellows and oranges achieved with polysulphides free of iron quickly turn brown when small amounts of iron are introduced. Glass sand generally contains enough iron to create this effect, but the addition of other compounds and variations in sand purity sometimes require the addition of iron amber glass oxide. The deep colour will fade with continued melting, allowing for further customization of the colour.

Excessive levels of amber glass oxide seem to result in a greyish colouration. This is a rare occurrence with glasses made with anthracite or carbon container glass colorant. The cooling rate and heat treatment play a large part in the formation of iron sulphides. If the concentration of alkali polysulphide is low, excessive formation of iron sulphides may cause greyish colouration.

For further information on the colouration of glass, contact your red iron oxide supplier.

General Information

Red iron oxide is a heavy and relatively hard oxide mineral. It is one of sixteen known oxyhydroxide variants and is the oldest known pigment used by major civilizations. It is considered the most important iron ore because of its high iron content and its natural abundance. Red iron oxide occurs most often in a soft, fine-grained, earthy form called red ochre, but can be found in naturally-occurring crystalline deposits in many different countries. Though it can be found in several forms, only these forms can be used as colourants and in the production of other materials.

Brown glass oxide gets its reddish colour from oxidised iron. Because it is nontoxic, it can be used for many applications other than a container glass colourant. These applications include ceramics, clays, dental composites, cosmetics, tattoos, concrete and cement, flooring and roofing, plastics and rubber, polishing and buffing, iron and steel production, data storage and processing, paints, primers, glazes, stains, anti-itch creams, heat-resistant coatings, fillers for wood and metal, pharmaceuticals, thermotherapy, and biomedical imaging and tissue marking.

African Pegmatite is a trusted red iron oxide supplier to buyers across several continents. Contact us for resources on how to make brown glass, as well as the many other uses of red iron oxide. Our specialists will be happy to answer any questions you might have and to point you in the direction of the minerals and materials that are suitable for your applications.

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