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OM4 Ball Clay and soluble salts

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'[OM4 Ball Clay] ... as some soluble salts which can give a brown coloration to the surface, so barium carbonate may be needed to precipitate these.'

I'm curious about this statement. My wee bit of chemistry knowledge imagines some sort of barium/salt crystals precipitating out of some sort of slurry solution?

Is there an alternative the barium? Will strontium work? Why would this 'precipitation be needed'? I understand somewhat how soluble salts work in shinos but what affect will 20% OM4 have in a clay body? Greenware will discolour? Will the clay store well? Is there a substitute for OM4 that does not have solubles?

Looking at the Periodic Table of Elements it's interesting to note that barium, other than gold, is the heaviest element that still might be in use today.

From up here the rabbit hole looks quite deep and inviting, like a clown, with a balloon.

<.<

>.>

:)

 

 

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OM 4 is just like a lot of other ball clays-very minor differences in most of them.-I have no idea about adding barium to ball clay-what temps is this statement applies to-diffently not my cone 10 area.

as to(Is there an alternative the barium? Will strontium work)

yes it can be direct substitute  but the color will be different and the same pin holing issues will apply.

Edited by Mark C.

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In claybodies the positively charged barium ions combine with the negatively charged sulphate ions and stop the sulphates from precipitating to the surface of the pot as the combination of the two produces barium sulphate which is insoluble. For a clay body with soluble salts and no barium the longer it takes for drying the more soluble salts will migrate to the surface. I think that the darker the clay the easier it is to see the soluble salts but they are probably in a lot of clays. As Hansen says barium "may" be needed. I've never had an issue with ball clay in glazes and soluble salts forming on the surface of glazes.

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the barium is used to prevent scumming of the soluble salts migrating to the surfaces. It is a common additive to earthenware clay bodies. Most majolica painters I know who mix their own clay add this...or use to.

 

Marcia

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