Natural Red Iron Oxide
Natural red iron oxide has many forms but there are only two which are used as colours and pigments for industrial use. It is one of the most abundant iron ores that can be found on earth. Iron oxide red has been used by many civilizations. Different variations of hematite can be found all around the world. Hematite is iron oxide, Fe2O3, and is the primary ore of iron, mined chiefly for the production of metallic iron.
The Hematite Factor
The reddish colour of soil is actually due to the presence of oxidised iron that is found mostly in the tropics. These soils carry very little affinity to water, as they are hard and dense. The importance this carries can be seen by the fact that the recorded use of haematite dates back to the 18th and 19th centuries. Ceramics and clay structures also held immense importance in those times, with these clays containing large proportions of iron oxide. When there was no concept of blotting paper, haematite was used as ink absorbent and was known as Devonshire sand. The applications are extremely vast and can be found in bridges, paints, pottery, pavers, substitutes of graphite and polishing glass as well.
Uses Of Iron Oxide Red
Red iron oxide is known by many names such as red ochre and bloodstone. Native peoples in the Indian subcontinent and the Americas extensively paid attention to it in geology and used it for decorative purposes and images. For exhibiting body paint, it was also used as a raw material. Hematite is the first choice ore as a source of iron for manufacturing iron and steel. The purest form of hematite is referred to as ‘rouge’ and it is used to polish glass and plates - capitalising on its abrasive qualities related to its hardness and strength.
A naturally occurring iron oxide ore is thin and scaly and is called micaceous hematite. It is reported that this material is used as a substitute or in the manufacturing of stoves replacing black lead. It also holds immense importance in petroleum and natural gas industries as a lubricant, pivotal in oil drilling (see later). Iron mine tailings are rich in haematite, which is how they can be used to manufacture bricks. Recycling is required because of the high alkalinity of the tailings; thus it can be found easily in recyclable waste streams in large volumes.
One of the choices to give pottery its shiny characteristic, hematite can be used. It has been used as pottery glazing and was mixed with enough water to make it easy to apply. In earlier centuries, tiles and bricks were decorated using haematite and pastes made of hematite.
Anti-corrosion paint is also made by using red iron oxide. Hematite is inert towards ultraviolet rays, making it the perfect anti-corrosive barrier. It can be used in paints and roof tiles to make sure that there is no little to no exposure to ultraviolet rays to the structure underneath. It can also shield from harmful effects of sulphur dioxide, ammonia and other pollutants. Even when making buildings, it can be used with other coarse materials such as cement. Iron tailings can help make unfired bricks due to their characteristics of being strong and durable after being reprocessed - a popular construction method in the developing world. In optimal pressure conditions and adequate water content, iron tailings can form non-fired bricks and other miscellaneous building materials.
Used As A Pigment
Dependability, extensive opacity and permanence are some of the most important qualities that colourants should have. When it comes to alkalis, haematite is indifferent towards them, whereas it is partly soluble in acids. Hematite does not react with most organic solvents. This pigment is extremely important in colourants, dyes and pigments.
The classic example of red iron oxide is as an inclusion pigment in the production of clay ceramics, such as tiles and bricks. Inclusion pigments are when a pigment is added to a clay before it has been fired into the ceramic form, such pigments do not dissolve in the media (i.e. the clay, water and other materials), but are dispersed evenly throughout.
The traditional terracotta pottery and ceramic colour is easily achieved with a simple addition of 4 to 10% (by weight) hematite to a clay and then firing it. Deep blacks can be achieved when manganese ores are used with hematite; whereas pink colours can be achieved when moderate amounts of zirconium silicate are used alongside hematite. For normal ceramics, no more than 5% by weight is used. 6 to 7% is considered a ‘high iron ceramic’, with wildly high amounts as high as 65% being responsible for ultra vivid, low porosity, porcelains when combined with kaolin. There are virtually limitless possibilities available by combining hematite with other metals in the pre-firing mixing stage.
There are many other uses of this pigment. When applied to glass, the red colouring on the glass helps protect what’s on the other side from UV radiation. It also provides a non-leaching contaminant, making it important for beer bottles, oils, wine and pharmaceuticals. It is also used as an additive in plate glass for automotive and residential use.
Another very important use is as fillers. This means that it is used as materials that are pastes which are used to smooth out surfaces and cover imperfections. The advantages of this can be seen in removing deep scratches from cars, metal-based items and even wood. Once it is dried and sanded, it will be ready to get primed and painted.
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