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Is boron that necessary in the 1230-1250 ºC / 2246-2282 ºF range?


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According to John Britt's  Complete guide to Mid-Range Glazes:

"Boron oxide broadens the firing range of glazes and enables us to lower the maturing range of cone 9/10 glazes to cone 6. Without boron oxide, cone 6 glazes would be limited to zinc glazes (Bristol) and high alkaline glazes.

What happens if we extend the firing temperature from cone 6 to cone 7-8 ? Does this still apply? What about other fluxes like CaO, MgO, SrO

Edited by thiamant
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I fire to 7 mostly. Boron is still one of the primary fluxes I employ. Calcium is only really starting to get going at cone 8, so if you want a fully melted glaze, you need it to start sooner than that. Magnesium and Strontium will both make a glaze matte. While a nice magnesium matte is a good thing to have in your glaze book, it’s probably not the only thing you want in it. I tend to use small quantities of strontium for the colour response, but if you want a clear base, you need some boron in there.

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Posted (edited)

Because I have to buy frits from germany, and they are quite expensive. It's interesting, I don't know any ceramist in Spain who uses frits in their glazes. Completely different culture and approach to ceramics and glazes...

Edited by thiamant
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Posted (edited)

I have tried Colemanite before with disastrous results. Because of decrepitation. I haven't tried Ulexite yet. But I heard it has a bad color response. There's a frit that I can use which is called PR1000 its very similar to frit 3134. So that's an option too. It costs 6.85€ / kg approximately, so slightly cheaper than American Ferro frits.

Edited by thiamant
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You could try using zinc as a flux in your magnesium matte but otherwise yes I do think you need some boron to get a good melt at cone 7. Zinc is not without it's problems though, pinholes for one plus it is a bit pricey.  Look up Bristol glazes to get an idea of the amount of zinc needed, there are a few cone 6 ones here on Glazy to give you a ballpark idea, would need to do some line blends, decrease the magnesium and add zinc.  Matt Katz has done some work with testing required amounts of boron needed from low to high fire. Chart below taken from this pdf on boron.

481718892_ScreenShot2021-04-30at8_01_26AM.png.130ee8323e2b8a2739f0e7f8b163b520.png

 

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I’m a big fan of using the materials that are available to you for lots of good reasons. Digitalfire has a listing for your P1000 frit, and out of the 2 most common Ferro frits, it’s closest to 3134. You would have to do some testing, but it looks like the kind of thing that you’d build a good cone 6/mid fire glaze around.

Among the reasons for using a boron frit local to you:  in conversation with my glaze supplier yesterday, we were discussing Ferro frit availabilities. The Ferro company is in the process of moving production from the US to Mexico, so there are supply disruptions for a lot of the more popular frits, including 3134 and 3124. While some distributors do have stock, it’s running low and rising in price accordingly. They are not, to anyone’s knowledge, going to be discontinued: the company is just in the process of setting up somewhere else. Couldn’t find an official timeline on when they expected to get back going, but I got the impression it might be next year (2022). 

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35 minutes ago, Min said:

You could try using zinc as a flux in your magnesium matte but otherwise yes I do think you need some boron to get a good melt at cone 7. Zinc is not without it's problems though, pinholes for one plus it is a bit pricey.  Look up Bristol glazes to get an idea of the amount of zinc needed, there are a few cone 6 ones here on Glazy to give you a ballpark idea, would need to do some line blends, decrease the magnesium and add zinc.  Matt Katz has done some work with testing required amounts of boron needed from low to high fire. Chart below taken from this pdf on boron.

481718892_ScreenShot2021-04-30at8_01_26AM.png.130ee8323e2b8a2739f0e7f8b163b520.png

 

Very interesting plot. Zinc is also widely used around here. Besides pinholing, some stains just dont work well with zinc glazes.

I'm getting the hang of glaze calculators, so it shouldn't be hard to replace frits with PR1000. But for some reason, matte glazes tend to use 3124 rather than 3134. 

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2 hours ago, thiamant said:

It costs 6.85€ / kg

Just for comparison, Ferro 3134 where I live is $160Canadian (108 euro)  for 22.68 Kg so just under 5 euro a kg. If I buy it in small 500gr bags it's $6.30 so approx 8.50 euro / kg. Your P1000 frit has over 1/3 more boron in it than 3134 so you will need a fair bit less of that versus 3134 in a recipe. 

I'ld price out a 5 gallon bucket of glaze using the P1000, in the grand scheme of things I don't think it will add much to the cost of glaze used per pot.

Edited by Min
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