Kiln kicked off early on bisque, can I glaze?

[Benzine]

1 hour ago, Pres said:

I have found  that I do better with the narrower range clays. Absorption rates for clay bodies should be posted, along with shrinkage rates at different cone temps. These criteria allow one to compare various clays before purchase. Standard Ceramic has always been good about posting these criteria

I have used Continental Clay in all of my classrooms over the years, and am happy with them, BUUUUT their lack of listed specifications is odd.  Almost every other clay supplier I've seen lists Cone range, shrinkage and absorption, and I am puzzled  as to why they don't.  I know of some professional potters that use some of their clay with a wide firing range (Firing in the middle of those ranges), and wonder if they've had any issues?

[Min]

3 hours ago, Sorcery said:

I personally don't like it when absorbtion numbers aren't listed.

I have tested Amaco's 6-10 #46 vitreous at 6-7 electric, and 9-10 gas.

I believe these longer range clays can easily be formulated to perform fine in their large window. 

Should do your own porosity/absorption tests with your firing conditions, fudge room of +/- 1% with many posted figures.

Without hijacking this thread too much, a quick note re wide firing range bodies... I'm using the classic 4 X 25 porcelain body at cone ten as an example because it's simple. At cone 10 it is 25 ball, 25 kaolin, 25 spar, 25 silica. To get this to vitrify at cone 6 the clay stays the same (50 total) but more flux is needed to get the silica into the melt, therefore spar goes up to 35 and silica can go down to 15. If you use the cone 6 version of this porcelain it will slump, warp and bloat at cone 10. If you fire the cone 10 recipe at cone 6 it doesn't have enough flux to melt the silica into the clay matrix, result will be a clay that isn't as strong as it could be (likely will also have other underfired issues as previously commented on). 

I looked up the Amaco 46 clay, from their description: "The bisque is very dense and semi-vitreous and is buff at cone 5 and soft gray at cone 10." if it works for your purposes then wonderful but it would be prudent for anyone using a wide firing range clay to do their own testing in regards to porosity/absorption at the cone they are firing.

[Syvanis]

Man I had a day off and I got a ton a responses. 

 

So far as getting a new clay I am looking at buying about a 1000lbs because we are going through the 600 I have at lightning speed. 

@Callie Beller Diesel Thank you for that suggestion I had no idea that was possible. I will try that out today. 

@Pres I am going to be in Denver this weekend I was hoping to check out the Clay businesses there, but sadly they seem to be closed on the weekends. I am going to chat with other Art teachers in the district and see what they suggest. 

Next question:

Let's say I do end up getting another clay. How do I handle that getting mixed up in the pug mill?

 

I have a shimpo that doesn't use a pressure gauge it just mixes it up and we do a lot of wedging after it pugs out. Do I need to clean the whole thing before switching clays? My students seem to be leaving almost as much extra clay as they are using (not quite that bad really). Right now at the end of each class I am having student toss extra class in the pugmill and I am pugging it at the end of each class. But there is still a bunch in the machine left. 

 

 

[oldlady]

syvanis, looks like you are swimming well having been tossed into that pool unaware.  thumbs up for you!

could you please post a photo of the kiln showing the "controls"?    

[Babs]

If so much waste is being genwrated, and you arenot wheel working yet then make sure students are guided to putting little bits of clay and clay they are working from in a plastic bag or similar AS THEY ARE WORKING.  At end of lesson these bit and remaining unused stuff can be wedged up by each student, slammed together with the folk at their table and with a few drops of water,can be reused next day , no need to pug up etc, just saying, old old teacher here...

[Syvanis]

Well, wish me luck. I am trying another bisque fire at cone 06.  

Here is a pic of the controls. 

[Sorcery]

No luck, Good skill and Observation!

Sorce