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Does Cobalt Carbonate Occur In Nature?

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I’ll be teaching a 2-hr clay class for high school students.  The goal is to incorporate art into a science/math/engineering focus.  An expectation is that they'll make a simple hand-built clay piece during the 2 hrs as well.  10 kids per session.


I’ve put together a number of concepts to cover.  One is that with raw, non-commercial glazes, what you see in the bucket is not what you get on the finished piece.  I’ll give them the recipes for 4 glazes and simply name the recipes Blue, Burgundy, Green & Brown.  They’ll also have cups of the raw glazes for a visual reference. The goal is to see if they can determine which recipe will produce which final color based on the colorant minerals in the recipes.  Which got me to thinking...why is cobalt oxide black in color and cobalt carbonate pink?


I checked DigitalFire and found the following, but still had a question.  From DigitalFire  - “The carbonate is produced from a liquid reaction between cobalt II acetate and sodium carbonate to produce red violet crystals that are recovered by filtration. The material is insoluble in cold water but will decompose in hot water.â€


So, am I correct in understanding that Cobalt Carbonate is not a material that is mined (or ever occurs naturally), but instead one that is always man-made using Cobalt Oxide?  I understand that chemically, each has a different number of oxygen molecules and that the oxide form is much, much stronger in color than the carbonate (true for oxides vs. carbonates in general). 


Thanks.  Who knows, there may be a future ceramic engineer or scientist who loves ceramic art in this group of kids! 

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There are no natural sources of the carbonate, as far as I know, but there are natural sources for cobalt.  The Chinese used a cobalt ore, asbolite, that had some iron and manganese in it, and it gives a more grayed blue that the straight carbonate.  Many potter who do work that is to some extent imitative of Chinese ware have tried with varying degrees of success to concoct a mixture that approximates the Chinese blue.

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