A wide range of browns, from light tan through to deep brown.
Of all mineral colourants, Iron Oxide is one of the most benign.It’s still recommended that standard protective practices and common sense be utilised, but on the whole it’s not too far dissimilar from handling a piece of rusty metal.
If a large amount collects in the lungs through inhalation it can cause problems, much the same as any dust-like particulates.Chiefly it’s considered an irritant upon inhalation, affecting both the lungs and gastrointestinal tract, but no lasting damage is believed to be caused from minor inhalation.Collections of iron dust in the lungs is called siderosis, a benign condition that does not appear to develop into fibrosis, unlike many other mineral dusts.
Ingestion of significant amounts can result in vomiting, diarrhoea and lethargy, along with more serious conditions such as gastrointestinal haemorrhaging, acidosis and leading on to coma and seizures – although large amounts of iron would have to be consumed before these were ever a threat.(Dangerously toxic amounts are in the region of 50mg/kg, so 3-4 grams for an average adult).
Iron oxide comes in a variety of colours and textures.As a general rule, there is little difference in end-product colour between yellow and red iron oxide, although red contains the highest percentage of iron so may produce the strongest, most vibrant results.Black iron oxide is the most coarse and will produce a spotted or speckled effect.Impure iron oxide is sometimes called crocus martis, and at the other end of the scale, synthetic products are available that provide a more even coverage and colour.Iron exists naturally in many clays, specifically the ones that appear red.Terracotta typically has around 5% iron in its makeup, which can have a substantial affect on the glaze.In high temperature reduction firings, the iron is chemically converted into a flux and can cause the glaze to become more viscous, increasing the risk of it running and fusing the pottery to the kiln shelf.
Titanium = Orange Zinc = Brownish Green Bone Ash = Red-Orange Reduction firing = Greens (celadons)/Blues (with only a very small amount of iron) Tin = Uneven Cream breaking to Reddish Brown across areas where the glaze is thin.