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
Shells
Table of contents
Key Data
Formula: Approx. 95% by weight CaCO3, the rest various trace oxides at <1% each
CAS: None
Other names: Seashells, cockles, mussels, oysters, scallops
Appearance: Various colours; complete shells or ground
Solubility in water: Insoluble
Thermal decomposition: It decomposes to lime (or quicklime) (CaO), starting at about 700°C but needing temperatures of 1000-1200°C for completion. In humid conditions the lime absorbs water, forming slaked lime (Ca(OH)2). Both lime and slaked lime are highly caustic.
Composition/Impurities
Approximately 95% CaCO3 by weight, the rest trace oxides such as silica and metals at <1% each.
There are stories about shells being toxic, especially in glazes, due to absorption of heavy metals. Whilst shellfish do absorb many toxic substances from the water, concentrations in the shells are only around 1 - 10% of those in the flesh, and are too low to be a health hazard to either the potter or the end user.
Uses
Whole shells may be used to support pots during firing in the kiln - after firing, the lime dissolves away as slaked lime.
Ground shells may be used as a substitute for whiting in clays and glazes.
Exposure Routes
as for whiting/calcium carbonate
Toxicity
as for whiting/calcium carbonate
Health and Safety Practice
as for whiting/calcium carbonate
Disposal
as for whiting/calcium carbonate
Regulatory Requirements
as for whiting/calcium carbonate