Finding the perfect clear

[Donna Kat]

Has anyone worked with Tony Hansen's G1214W Clear? I had thought I had found the perfect clear for our studio when I found this glaze. It did not craze on Standard clays. It was crystal clear and it behaved well with all the underglazes used with it. Then it started turning milky. I weigh the glazes so it was not an issue of thickness or application. I worried about contamination but after several new batches for testing I convinced myself that no, it was the glaze. Some people suggested that this was really a ^7 glaze and that would explain the glaze becoming milky over time if in fact the kiln had been firing hot when I first started using the glaze after a change in elements and as I adjusted the firing for our ^6 firings the problem showed up. 

So the question and/or challenge after this long intro is has anyone else had experienced with this glaze? Since upping the boron is probably going to up the cloudiness does anyone have a suggestion for lowering the temperature without upping the F3134? Finding a clear glaze that fits a lot of clays is very difficult. Finding that plus one which is crystal clear and does not change the color of the underlying clay and underglazes is near impossible. this is the most promising glaze I have found.

[Norm Stuart]

Donna - In general, glazes become yellow from Iron and blue from Boron.

There's two ways for G1214W to cloud up, especially with slower cooling.

It has a generous amount of Boron and Silica which can produce "Boron Clouding" which is a blueish white haze. You can limit this by increasing the percentage of Alumina.  This is most likely what you're seeing.

While this recipe has far less Calcium than a Calcium semi-matte, calcium from the Wollastonite can cloud up a glaze with a slow-cool. A handful of wollastonite is essentially the ultimate calcium-matte.

You may want to try "Norm Stuart's Clear Clear ^6". The Boron level is less, but so is the Alumina, so this may not fix your problem.

But the percentage of Calcium is lower than G1214W. And there's far less iron by using New Zealand Kaolin. The 1% Veegum bentonite also adds fluorine as a flux which helps keep glazes clear in my experience (or at least in my imagination).

Both glazes are much clearer than the Cone 06 low-fire "Idiot Proof Clear" which always has a bluish green cast to it from the sickly-high 20% boron level it contains to make it melt at Cone 06.  But the Alumina level is also much higher in "Idiot Proof Clear" so there's never any boron clouding, just a bluish color.

[George Lewter]

I recommend this glaze. I have never seen it cloudy, yellow, or blue, (though it will sometimes trap tiny air bubbles). I use it exclusively on my slip decorated pieces, As you can see on this link, I've used it for 7 years

Recipe Name:  5-6 Clear
Cone:  6     Color:  clearFiring:  Oxidation     Surface:  Glossy
Amount Ingredient

40          Feldspar--Kona F4 (substitute Minspar 200 if you don't have any leftover F4)

30          Gerstley Borate--1999

20          Ball Clay--Old Mine #4

10          Silica

100         Total

[Norm Stuart]

George  - Looking at the comparison with G1214W, the glaze you use:

1.) has far less calcium, so no calcium semi-matte look with a very slow-cool;

2.) has 40% more boron than G1214W, BUT it has a lower 8.0 SiB:Al ratio - so too much alumina.to silica for boro-silicate crystals (boron clouding) to form.

[Gina Skillings]

When I want a clear that doesn't go milky I use John's and Ron's Glossy Clear Liner Glaze from Mastering Cone 6 Glazes. I've not had any issues with it and I use a slow cool program. 

[Norm Stuart]

We too used the Mastering Cone 6 Glaze Glossy Clear Base #1 for years.  Their #2 base with more silica can run if over-applied.

Gina Skillings said:

When I want a clear that doesn't go milky I use John's and Ron's Glossy Clear Liner Glaze from Mastering Cone 6 Glazes. I've not had any issues with it and I use a slow cool program. 

[Gina Skillings]

For clear I use the one they designated as a clear liner glaze on page 97. They mention that it is more transparent than base glaze 1. It uses G-200 Feldspar which I still have but I've made note of the changes for using G-200 HP. 

[Donna Kat]

I have tried almost every glaze mentioned and only Bates clear and G1214 was crystal clear and behaved well with underglaze and iron. Bates crazed and G1214 did not. It is time to go back to testing but the studio has shut down so I now must go at my own pace which is much slower than 100+ people.

Norm Stuart said:

Donna - In general, glazes become yellow from Iron and blue from Boron.

There's two ways for G1214W to cloud up, especially with slower cooling.

It has a generous amount of Boron and Silica which can produce "Boron Clouding" which is a blueish white haze. You can limit this by increasing the percentage of Alumina.  This is most likely what you're seeing.

While this recipe has far less Calcium than a Calcium semi-matte, calcium from the Wollastonite can cloud up a glaze with a slow-cool. A handful of wollastonite is essentially the ultimate calcium-matte.

You may want to try "Norm Stuart's Clear Clear ^6". The Boron level is less, but so is the Alumina, so this may not fix your problem.

But the percentage of Calcium is lower than G1214W. And there's far less iron by using New Zealand Kaolin. The 1% Veegum bentonite also adds fluorine as a flux which helps keep glazes clear in my experience (or at least in my imagination).

Both glazes are much clearer than the Cone 06 low-fire "Idiot Proof Clear" which always has a bluish green cast to it from the sickly-high 20% boron level it contains to make it melt at Cone 06.  But the Alumina level is also much higher in "Idiot Proof Clear" so there's never any boron clouding, just a bluish color.