Blue centre glaze recipe

[Jessicak]

Hey guys,

I’m hoping someone can help me out with a glaze recipe. I have been using Spectrum 250 satin clear on a clay body of white stoneware PB 157-2145 with 3.5% best black mason stain mixed into the body. I can get a really nice decorative effect as you can see in the attached. 
 

Unfortunately I can’t get hold of that glaze any more and I am struggling to find a recipe which will produce the same effect. I know that the over firing of the glaze is causing it to run and pool at the base, but not sure what is causing the lovely blue colour. 
 

If anyone could point me in the direction of a recipe or even just let me know where the blue colour is coming from, that would be amazing 

[Mark C.]

I cannot help you with finding this glaze but can say that the pool of thick glaze in bottom is no good as its to thick and crazed to the moon (cracked) and this bowl will leak if not now than very soon..When glaze gets to thick it will develop flaws . I call that effect broken windshield -its ok for sculpture but not functional wares.

[Jessicak]

31 minutes ago, Mark C. said:

I cannot help you with finding this glaze but can say that the pool of thick glaze in bottom is no good as its to thick and crazed to the moon (cracked) and this bowl will leak if not now than very soon..When glaze gets to thick it will develop flaws . I call that effect broken windshield -its ok for sculpture but not functional wares.

Hi Mark,

Thanks for your response. I’m aware of the crazing and the issues that come with this. This glaze is for decorative rather than functional pieces 

[Min]

53 minutes ago, Jessicak said:

If anyone could point me in the direction of a recipe or even just let me know where the blue colour is coming from, that would be amazing 

The Mason Best Black stain you are using contains iron, cobalt and chrome, the blue is from the cobalt where the glaze is thicker where it's pooled. That shade of green is from the cobalt plus chrome and iron. Look for a fluid glaze recipe, that doesn't contain zinc (zinc makes chrome turn brown), and run some tests. Alumina is one of the things that makes a stiff glaze, to make a glaze runnier reduce the alumina in the recipe. Easiest way to do this is reduce the clay content in the recipe, usually this will be EPK. 

[JohnnyK]

Is there a possibility that that is a pool of crazed glass instead of glaze?

[Jessicak]

2 hours ago, Min said:

The Mason Best Black stain you are using contains iron, cobalt and chrome, the blue is from the cobalt where the glaze is thicker where it's pooled. That shade of green is from the cobalt plus chrome and iron. Look for a fluid glaze recipe, that doesn't contain zinc (zinc makes chrome turn brown), and run some tests. Alumina is one of the things that makes a stiff glaze, to make a glaze runnier reduce the alumina in the recipe. Easiest way to do this is reduce the clay content in the recipe, usually this will be EPK. 

Ah I see, thank you! I’ll do some experimenting 

[Bill Kielb]

6 hours ago, Jessicak said:

Ah I see, thank you! I’ll do some experimenting 

You are welcome to this glaze if you like. I tired of experimenting as it was pretty temperature sensitive and went golden I think over cone six. It’s titanium based color wise and started as a Bristol glaze which we converted to a gerstley glaze. It is a true matte which was designed to begin melting closer to cone 4 which means depending on the crystal formation it looks blue or violet blue. Placing it over a glossy glaze it does run and produce some interesting results.

 

[Chilly]

On 1/1/2021 at 5:23 PM, Jessicak said:

I’m aware of the crazing and the issues that come with this. This glaze is for decorative rather than functional pieces 

You may think it's for decoration, but there is no knowing what a future owner will do with something that looks like a bowl.   Just saying