A fairly uninteresting light khaki green.Oxidisation has yellow tendencies whereas reduction leans to brown.Excessive amounts can cause grey.
Chromium Oxide is considered extremely toxic and should not be used for funtionalware under any circumstances, as the toxins can leech from the glaze into food and drink.In its mineral state, Chromium Oxide is dangerous for both inhalation and ingestion, although studies suggest approximately only 2-3% is absorbed when ingested so the paramount concern surrounds inhalation, except in large quantities of ingestion which may cause severe ulceration and gastrointestinal bleeding.Studies suggest approximately 4mg/kg body weight can cause dangerous ulceration, whereas 15-25mg/kg body weight is considered a lethal dose, resulting in gastrointestinal burns, haemorrhage and damage to both the liver and kidneys leading to death.It is a moderate to severe skin irritant on contact, causing dermatitis, allergic sensitisation and caustic burns.In particular, contact with the eyes should be avoided.
Several components of Chromium, including Chromium Oxide, have been implicated in lung cancer when the dust has been inhaled and it has been designated as Group 1 in terms of the inhalation cancer classification (definite carcinogen affecting humans).The carcinogenic effects of ingested Chromium Oxide have not yet been confirmed so the carcinogen rating remains at 3 (unknown), however, it is still highly toxic upon ingestion for the reasons given above.In addition to the mineral dust, the fumes of Chromium Oxide being fired in the kiln are considered very dangerous.Potters using this mineral must plan for adequate ventilation and avoid breathing the fumes or allowing others to do so.Further long term effects range from asthma, chronic bronchitis, nasal septum ulcers (leading to perforation in severe cases), sinusitis, rhinitis and other similar disorders of the respiratory system.
At cone 6 and above Chromium Oxide becomes volatile and may spit, causing streaking or smoky effects on nearby pieces, therefore it's often only used to temperatures up to 1,200C and is advised not to go beyond 1,240C.The length of the firing has little effect, with both long and slow firings producing the same results.Likewise, there are no differences between oxidation and reduction firings.For oxide washes a solution of 5% Chromium Oxide is recommended, and in glazes approximately 3% will be an effective colourant.
Iron = Grey/Grey-blue Manganese = Browns Calcium or strontium = Pink/Crimson/Burgundy Lead soda and Zinc = Orange Lead soda with alkalisers = Yellow Tin and high levels of boron = Red/Purple High alkaline/high boron levels = Clear bright green Low level of Cobalt with boron or soda, no zinc = Teal/Peacock Green Lead soda and high percentage of Chromium Oxide (4-5%) = Pink Lead in low alumina and low temperature = Red and bright orange Tin and low percentage of Chromium Oxide (0.5-1%) and strontium or calcium, thickly applied = Grey/Pink Tin and low percentage of Chromium Oxide (0.5-1%) and strontium or calcium, with zinc = Warm brown