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Lbegley

underglaze growing algae

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I have a vanadium underglaze recipe that changes color from yellow to green (only wet in the container, it  fires yellow).  The color shift makes mixing colors difficult, and I’m hoping someone here has a solution to curb the growth of whatever microbes are changing its color. 

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bleach works.  just a little unless the staining has spread throughout the liquid.   happens with my slips which i use for several years and i just bleach it out.

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I make it and it lives in a windowless room, in an opaque container, so I guess you’re right and it’s probably some other microorganism, not algae.  Whatever it is, it only lives in the vanadium underglaze, none of the other mason stains seem to change color, but the base does bubble when it’s freshly made like it’s fermenting!   I’m going to try some vinegar and see if a ph change is enough to make it less appealing to the buggers. 

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@Lbegley, a tiny bit of copper carbonate added to brushing medium stops the gums in the brushing medium from rotting, magma glaze additive suggests using copper also. The amount used is so small that it doesn't effect the colour. Same principle would apply to underglazes as glazes. By weight it would be 0.04% copper carbonate, like everything ceramics, if you try this test a small amount first.

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5 hours ago, Min said:

@Lbegley, a tiny bit of copper carbonate added to brushing medium stops the gums in the brushing medium from rotting, magma glaze additive suggests using copper also. The amount used is so small that it doesn't effect the colour. Same principle would apply to underglazes as glazes. By weight it would be 0.04% copper carbonate, like everything ceramics, if you try this test a small amount first.

Thank you!  I will test copper carb. 

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Update!  I added 0.05% copper carb to my engobe base, and it seems to have worked!  It doesn't effect the color fired and after a month it hasn't changed in the bottle (my control batch is green and stinky, so success!).  The only bummer is that it is such a small percentage, that in order to measure it, I need to make a pretty large batch. 

I also tried vinegar which also worked to keep the engobe changing color, but changed the consistency, and the solids collected at the bottom.  

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Measure 1 gram. Using a knife or other straight edge, divide the pile by half, then divide a pile by half, then divide the pile by half, then divide by half. This gets you to 0.0625

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