Boron quantity at cone 6?

[Beebop]

I see references to recommended stable UMF levels for cone 6 glazes, usually around 2-3 Si / 0.2-0.3 Al with 0.15 B to get the chemistry to melt. But, could one use melt higher levels of Si and Al at cone 6 so long as more B was also used?  And if that works, is there a reason why lower Si & Al levels are recommended, other than the cost of frit? And if that doesn’t work, why not?

At the other end, I am also curious to hear what people have to say about the stability of a glaze with a 3:7 R2O:RO ratio with Si and Al levels low enough to melt at cone 6 without adding boron. I am under the impression that that’s a bad idea because there aren’t enough glass formers to make it stable, but it really seems like a good idea in my head. Thinking about ash glazes in particular. I’m not using toxic colorants that I’m concerned will leach, but I want to avoid making beautiful glazes that degrade rapidly. 

Just want to poke at the rules a bit and see what sticks. And yes I will test for myself, just looking for guidance first. Thanks all!! 

[Bill Kielb]

0.15 Boron  has been shown to be effective for cone 6 (Katz: https://www.ceramicmaterialsworkshop.com/cmw-blog/getting-boron-levels-right) and I have used it for a wide variety of Si:al ratios. Too much Boron is a thing fo sure but .45 boron generally  gets you down to cone 04. Boron can come firm Fritts and of course gerstley or gillespie borate among other sources. Reading the above may give some additional insight about the too much part.

0.3:0.7 is in general considered a very stable (ideal) ratio and as we diverge from this glazes tend to be less durable. 0.2:0.8 is the lowest I will go when designing. If you are deriving from limits, then there are variations to them and some crossover as well, so in my view and experience general guidance and trend…………. Maybe more like practical ranges than a limit IMO

Its a bit harder  to get things to fully melt at cone six without boron (boron is easy) and of course material limitations so neph sy is often a goto for lower Si:al. Bristol glazes get there but involve fairly specific range of zinc.

You could always test. A cool idea I have seen is gloss meter and lots of dishwasher cycles. While not perfect nor an accurate indication of leaching , it would give you a sense or durability  and surface degradation ………..and it’s simple to do.

[Min]

13 hours ago, Beebop said:

Thinking about ash glazes in particular.

Have a look at cone 6 ash glaze formulas. One below to have a look at plus a popular fake ash recipe. Have a look at the SiO2 and Al2O3 levels. Granted ash figures are going to vary widely dependent on the ash used but it gives you a general idea of the chemistry. To get the runny rivulet property of an ash glaze it will to be fluxed with calcium and have low alumina. The Hanna's Fake Ash has higher alumina levels but still are low. Granted some silica and alumina could be pulled from the body but ash glazes are traditionally used on the outside of pots for decorative use.

Just to make it easier a limit's chart also. Many of the really interesting glazes with visual texture come from glazes outside the "limits".

[Beebop]

13 hours ago, Bill Kielb said:

0.15 Boron  has been shown to be effective for cone 6 (Katz: https://www.ceramicmaterialsworkshop.com/cmw-blog/getting-boron-levels-right) and I have used it for a wide variety of Si:al ratios. Too much Boron is a thing fo sure but .45 boron generally  gets you down to cone 04.

My concern is more about the quantity of Al and Si rather than the ratio of the two. For example, what happens if you add 0.15 boron to a cone 10 glaze and fire to cone 6; does it melt? If not, can you add higher levels of boron to a cone 10 glaze to melt at cone 6?   I watched the CMW cone six video series, but this point of altering boron for different chemistries was not brought up which is why I brought it here. I guess the way I’m thinking about it, the lower Si and Al recommendations for cone 6 compared to 10 mean that there’s more flux in the mix to lower the melting temp, and 0.15 boron is also added. But as you increase or decrease the quantity of flux in the mix, shouldn’t you have to also decrease or increase boron to compensate if you want to melt at cone 6? And if so, why is 0.15 a golden standard for cone 6 if it’s variable?

I’m gearing up for tri-axle blend tests, just trying to pick the three variables to alter with each test. I guess the answer is to just alter boron levels and find out!  

[Bill Kielb]

43 minutes ago, Beebop said:

My concern is more about the quantity of Al and Si rather than the ratio of the two. For example, what happens if you add 0.15 boron to a cone 10 glaze and fire to cone 6; does it melt? I

Yes in general it melts nicely .15 is not a gold standard but his testing shows a fairly linear relationship. Too much boron has its own issues so if you watched the video or you read the page I attached you will notice color development is also an issue. But if you go back through your notes you can find a degradation graph as well. While only tested for one flux ratio and one si/ al amount it does show the least degradation at 0.15 fired to cone 6.

Here is an interesting thought though, I have on occasion added more boron to get an earlier melt to make sure the glaze is a bit more fluid. It’s fired reaction under gravity is hard to predict though and the realization that straying too far likely begins to increase degradation.

it would be great if you want to run a bunch of degradation and maybe color tests though, adding to that research. You could  test different amounts of si /al varying boron under one flux ratio within some reasonable interpolation then do degradation and color shift on those samples and try to unify across a broader range without having to conduct as many tests. Then dial up a new flux ratio and repeat.

[Beebop]

31 minutes ago, Bill Kielb said:

Yes in general it melts nicely .15 is not a gold standard but his testing shows a fairly linear relationship. Too much boron has its own issues so if you watched the video or you read the page I attached you will notice color development is also an issue. But if you go back through your notes you can find a degradation graph as well. While only tested for one flux ratio and one si/ al amount it does show the least degradation at 0.15 fired to cone 6.

it would be great if you want to run a bunch of degradation and maybe color tests though, adding to that research. You could  test different amounts of si /al varying boron under one flux ratio within some reasonable interpolation then do degradation and color shift on those samples and try to unify across a broader range without having to conduct as many tests.

Yes it’s the testing boron against different flux / Si / Al levels that I’m curious about. Just looking for some insights before I fall down the testing rabbit hole.   

I think when people ask me what I make as a potter I should just say test tiles. I just can’t seem to get to the point where I’m glazing actual pots, too obsessed with asking- what happens if I fall down any one of these rabbit holes? 

[Bill Kielb]

1 minute ago, Beebop said:

Yes it’s the testing boron against different flux / Si / Al levels that I’m curious about. Just looking for some insights before I fall down the testing rabbit hole.   

I think when people ask me what I make as a potter I should just say test tiles. I just can’t seem to get to the point where I’m glazing actual pots, too obsessed with asking- what happens if I fall down any one of these rabbit holes?

Lots of room in pottery. If you enjoy the research and you share Its laudable IMO.