Cone 6 White Engobe Liner + Clear Glaze Questions

[Polydeuces]

Hey y'all,

 

I'm looking for some solid advice on the title of the post. 

 

I was considering using this recipe which I saw on ceramic arts daily:

 

Kaolin: 15

Calcined Kaolin: 35

Talc: 5

Nepheline Syenite: 15

Silica: 15

Borax: 5

Zircopax: 10

 

And then a clear recipe called "Campana Clear" which is in John Britt's midrange glaze book, which I have tried a few times and seems to go well.

 

First of all, I was curious about what temperature I should calcine the kaolin at, and if a different kaolin is recommended over EPK. I was thinking of soaking at cone 020 for 30 minutes. Secondly, I was curious about different colors, say if I were to use Alberta Slip in a 50:50 raw:calcined mix, or Newman Red, in place of the clays. Would this work?

 

Finally, I was curious about application to bisque-ware. Is there anything I should do or be aware of, other than making it pretty thin? I'd like to apply it by dipping/pouring. I looked up some stuff on digitalfire and admittedly got a little overwhelmed when they started talking about thixotropy & $1000 wall-mounted blenders.

[Dick White]

Regarding calcining the kaolin, all you need to do is fill a bisqued unglazed bowl with your usual kaolin and include it in your next bisque firing. It will be chemically changed by driving off some extra hydroxyls in the kaolin molecules as it heats, but will be physically similar, i.e., still a white powder.

[Polydeuces]

Regarding calcining the kaolin, all you need to do is fill a bisqued unglazed bowl with your usual kaolin and include it in your next bisque firing. It will be chemically changed by driving off some extra hydroxyls in the kaolin molecules as it heats, but will be physically similar, i.e., still a white powder.

 

Thanks! Can I also calcine the alberta slip at that temperature without compromising its ability to do its thing? 

[Dick White]

I would think the alberta slip could be taken up to normal bisque temperature because it is just another clay material. Some other things that need calcining to "dry" them out can't go that hot, such as zinc oxide.

 

Edit: what Min said - regular bisque is too hot for alberta. Ignore my comment.

[Min]

I found 04 was too hot for alberta slip, it goes kinda gritty / sintered and the glaze doesn't seem to mix up properly,  020 range works.

 

edit: I would be looking at adding ceramic stains, colouring carbonates or oxides to your kaolin original based engobe if you want to add colour. (might not need the zirco)

[neilestrick]

I do not think Alberta/Albany could be a direct substitute for the kaolin, because they melt at much lower temps. They are more like a terra cotta than a kaolin.