A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 1-9

Cobalt Monoxide

Key Data

Formula: CoO
CAS: 1307-96-6
Other names: Cobalt (II) Oxide, Cobalt oxide
Appearance: Grey-black powder
Solubility in water: Insoluble
Melting Point: 1933°C



A strong blue colourant and a flux.
Note that this is not the material most potters use; for that, refer to cobalt oxide.

Exposure Routes

Skin and Eye Exposure

May cause an allergic skin reaction with prolonged exposure. This manifests as eczema and erythema.
Not a skin or eye irritant.

Skin Absorption

Not absorbed through the skin.


May cause asthma or an allergic reaction. Not an irritant.
Because cobalt monoxide is soluble in the lung fluids, up to 50% of inhaled material may be absorbed. This also means that the rate of absorption from the lungs is faster than for the relatively insoluble oxide and carbonate.


Due to its solubility in acids, its toxicity in the digestive tract is similar to soluble cobalt compounds. Estimates of the amount of cobalt absorbed into the body lie between 13 and 34%.




Not toxic.


Whilst very high levels of inhalation may be toxic, the levels are much higher than will be encountered in a studio,


Due to its low level of uptake into the body, and the quantities used in a potter's studio, it can be viewed as not being toxic.

Repeat Dose


No effect.


In animal tests, lesions formed in the lungs with a dose greater than 1mg/m3.
The USA found that effects occur at a range of 0.015–0.13mg Co/m3; soluble compounds (not the carbonate) will occur at lower levels.
The EU found an NOAEL of 0.12mg/m3 in humans.
The USA has set an NOAEL of 0.0053mg/m3, and a LOAEL of 0.0151mg/m3, for all forms of cobalt. An MRL of 0.0001 mg cobalt/m33 has been derived for chronic duration inhalation exposure to cobalt. As this includes cobalt compounds that are both soluble and insoluble in the lungs; this level is probably excessively conservative for the low solubility of cobalt carbonate.


If excessive cobalt is ingested over a long term, it may affect multiple systems in the body. However, the safe levels of ingestion are set for all cobalt compounds, and cobalt oxide's uptake into the body may be a tenth that of more soluble compounds, so these levels can be taken to be very conservative.
In the USA an MRL of 0.01mg Co/kg body weight / day (0.6mg/day for a 60kg person) has been set by the ATSDR for intermediate duration (14 - 365 days) oral exposure to all forms of cobalt.
In the Netherlands, a TDI (Tolerable Daily Intake) of 1.4𝜇g Co / kg bw /day has been set.


It is not genotoxic.


Whilst some cobalt compounds can be carcinogenic if inhaled, this does not apply to insoluble cobalt compounds such as cobalt oxide.

Reproductive Toxicity

Whilst sufficiently high doses may damage fertility, and are suspected of damaging the foetus, in the studio the small amount of cobalt used means that this level of exposure is very unlikely.

Health and Safety Practice

Most potters do not use this material directly, using cobalt oxide or carbonate, with the monoxide forming during firing. This is no bad thing, as it is more soluble in both the lungs and digestive tract, and so more toxic than other forms of cobalt.
Because cobalt is used in very small percentages in most glaze recipes, the risk level is not too great. However prudence would indicate wearing gloves when you come into contact with it, e.g. if you put your hand into a glaze to test its consistency, to minimise the risk of becoming sensitised to it. Otherwise, normal dust precautions will also protect you against cobalt.


Very toxic to aquatic life.

Regulatory Requirements

Dust Limits

These are for all cobalt compounds, and the levels are for the proportion of cobalt, not the compound.

ACGIH (USA)0.02mg/m3TWA, 8 hr day
OSHA (USA)0.1mg/m3PEL: TWA, 8 hr day
NIOSH (USA)0.05mg/m3TWA, 8 hr day
ATSDR (USA)0.0001mg/m3Long term MRL
HSE (UK)0.1mg/m3TWA, 8 hr day as Co
RIVM (NL)0.0005mg/m3TCA: tolerable concentration in air