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Substitute For Lead Bisilicate


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I have a low fire transparent glaze recipe that makes a nice glossy glaze with a good colour response to various oxides. It has crazed slightly and would be even better for me if that didn't happen.

I know the lead bisilicate helps with the colour response but am not sure about sticking with this as my 'go to' recipe because of the lead.

This is for use on a smooth, white earthenware, sometimes just as a transparent over underglazes or oxide washes, but also as a base with oxide/stain additions.

 

Can anyone suggest a possible substitute? And if it helps with crazing that would be even better! I know I'll have to re-test, but a starting point would be helpful.

The recipe is -

Lead bisilicate 65

Whiting 10

Potash feldspar 15

China clay 10

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Hi Celia,

You're probably going to be looking at Zinc or Boron based glazes, but you won't get the same colour response, nor will you get the same gloss as you get with lead.

What temperature do you fire to, so I can be a bit more specific?

Are you against lead because of risks to yourself? The lead bisilicate is pretty well insoluble in the body, so as long as you keep exposure levels reasonable with normal dust precautions there shouldn't be any significant risk.

If you are doing functional ware then you can keep the lead out of the area in contact with food - e.g. on the outside of jugs - and use a lead free glaze inside. Or, so long as you don't use copper, you can make food safe lead free glazes - you can get the same lead leaching test kits on eBay that the FDA field workers in the US use (I forget the name, the seller is somewhere round Poole), or if you do a lot it is only about £40 to get a test house to do a more accurate and official test for you.

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Its been decade since I worked in your temp range but nothing melts like lead.

I gave it up long ago for obvious reasons when I was doing raku work and that was in the early 80's.

Good luck on a sub.

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[What temperature do you fire to, so I can be a bit more specific?

Are you against lead because of risks to yourself?

If you are doing functional ware then you can keep the lead out of the area in contact with food - e.g. on the outside of jugs - and use a lead free glaze inside. Or, so long as you don't use copper, you can make food safe lead free glazes - you can get the same lead leaching test kits on eBay that the FDA field workers in the US use (I forget the name, the seller is somewhere round Poole), or if you do a lot it is only about £40 to get a test house to do a more accurate and official test for you.

 

Thanks Tim - glaze firing to around 1100oC. I appreciate that I can keep the lead glaze to the exterior, but I do like copper!!! I'll look for the leaching test kit - worth knowing about thank you! I've been to the ceramics suppliers today and talked this lead issue through with various technicians - then priced up the ingredients cost and there was little savings to be had over buying one of their glaze mixes! The only benefit seems to be that you know the exact contents if you mix your own, which is helpful if things don't turn out well and you're then trying to troubleshoot.

 

Sputty - don't think I'll need to worry about EU regulations - one of the few benefits of being 'out'!!! I'm going to try an alternative recipe that Gerry at Potterycrafts suggested (using ingredients I already have) and see how I go! Re AP - the recipe above was from a glaze workshop I did with John Masterson (AP Chairman), who, along with most others I've spoken to would similarly not be overly concerned if used on outside of ware and suggested testing if I wanted to seek reassurance. Interesting comment about endocrine disrupters - especially as one ceramic supplier expert tells me that Lead bisilicate has been removed from the list of toxic substances - can't remember the name, but it no longer bears the skull & crossbones symbol, but food standards have apparently yet to catch up. I expect that will promote a flurry of posts here!

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They have taken out most lead in most low fire glazes here in the USA-thats the long term plan here at least.

I know theoretically you can encapsulate lead and have the glaze be safe but its a non issue for me working at cone 10 and 11 as lead does not exist at that temp. Its a low temp flux which is say low fire clay 1800F or raku temps. I have not done low fire since 1974-raku in the 70's and early 80's and it was a great flux.Still have a bag of 6040 frit.

I turned in my 50 # bag of white lead long ago to a hazmat day in our community  along with old lead paint and my gallon of red lead paint like the golden gate bridge was painted with long ago.

Lead is something I just do not want around me any more. That said I have many other chemicals most would not be happy with.

All my work is for food use on a daily basis. Reduction fired to cone 11.

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Try Ferro Frit TR-1132.  It's one of the few remaining frits with "lead" contents that you can still buy.  We use it in our studio as a sub for a few older items we can't get anymore.  Testing definitely required, but at least its a place to start!

 

Funny thing is I'm currently staring at a 5-gal bucket about half-full of Litharge that I recently found in my storeroom from a bunch of things donated a few years ago.  Fun-Dip time, yum!

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