Predominantly browns with Purples under certain conditions.
As with many other metallic dusts, inhalation of Manganese Dioxide can cause ‘metal fume fever’, a disorder that presents similarly to the flu with a wide range of symptoms including nausea, muscular and joint pain, fever, chills and headaches. In addition, inhalation has been implicated in bronchial asthma, pulmonary pneumonitis, acute respiratory infection, and if to a chronic degree, pulmonary inflammation and the narrowing of the airway.
Ingestion of Manganese Dioxide can cause hypotension, vomiting, dehydration, diarrhoea, metabolic acidosis, and in severe cases, multi-organ failure leading to death. A build-up in the brain of Manganese Dioxide will result in neurotoxicity and Parkinson’s-like symptoms.
It is not easily absorbed through the skin so the risks of toxicity through this route are minor – although standard precautions of latex gloves while glazing are still strongly recommended due to the likelihood of hand contamination leading to ingestion. As with most metallic minerals, direct contact may cause irritation and dermatitis.
Manganese Dioxide will convert into Manganese Oxide at temperatures in excess of 1,080C at which point it will produce purple colouration when mixed with silica. This process releases oxygen which can have an effect on the surface texture of the glaze, potentially causing pinholes or blisters. A glaze containing 5% Manganese Dioxide will begin to crystallise, and at approximately 20% it will form a metallic surface which is unsuitable for functionalware.
Alkaline glaze = Blue-Purple/Plum Lead = Purple-tinged Brown Tin = Coffee Brown (if below 1,080C) Cobalt = Black or Blue-Plum (dependent upon Cobalt/Manganese ratios) Cobalt and Iron = Black (a ratio of 16:8:1 Iron, Manganese Dioxide and Cobalt)