Best Clays to Use for Single Firing

[George Lewter]

     While many clays may be used for raw glazing and single firing, some are bound to be better than others at taking the shock of getting a bath of glaze at the leather hard or bone dry stage. Steven Hill formerly used B-mix 10, but felt he was getting too much bloating with it. He used one of Standard Ceramic Supply's porcelains for a while, and is reportedly now using Tom Coleman porcelain which is made by Aardvark Clay.

This is the place to report your results with various clays and the techniques you use for raw glazing.   

 

[CM Partin]

You need enough clay in your glazes (bentonite, etc...) to allow the glaze to shrink with the greenware, B-mix 5 should work well.

[John Lowes]

I have my fingers crossed, as I have a three Laguna ^5 B-mix pots, along with a couple of Highwater Red Earthenware pots, in a firing now, all raw glazed with a plethora of glazes. I poured the interiors and sprayed the exteriors. I had some time between glazing the interiors, maybe 2-1/2 hours, and spraying the exteriors. I did not note any problems, of any sort, during or after the glazing. I put them all in the kiln last night with a shop light in the kiln to warm them up and keep the evaproation going, before starting the firing this morning. I am using a slow bisque schedule on a kiln sitter equipped kiln, with a cone 7 in the sitter, and a 4 hour run on all Low after the sitter drops and the cone plaque is checked. I will know how it went Tuesday evening. I guess you could say, in poker terms, I am "All in".

[John Lowes]

The results are in and I am pretty excited and pleased with the results:

http://cone6pots.ning.com/photo/albums/single-fired-work

Most of this is Laguna B-Mix, but I also have a couple of Highwater Clay's Red Earthenware and one Standard 365 Porcelain. The glazes in this group are mostly commercial with a couple of homemade thrown in. I fired a slow bisque with a Cone 7 in the Kiln Sitter, then downfired for 3 hours to 1525 degrees F.

[George Lewter]

Laguna B-Mix 5 is a pretty smooth white stoneware with almost no iron or other coloring oxides that would tend to muddy or break through a glaze. It is very plastic and throws easily.  I've noticed that seams where clay comes together in wedging, don't weld together as well as with some other clays, so tossing the spiral seams down on the wheel head is asking for trouble. I've had occaisional problems with handles breaking loose in drying.  My latest batch of 9 mugs with handles attached by scoring and painting the join surfaces with a solution (1 part white vinegar to 2 parts water) before joining  all came out beautifully without any excess slip needing to be removed or blended in.

     Raw glazing green B-Mix is a little tricky, though I haven't yet tried glaze application at the leather hard stage.  At the bone dry stage I can pour the interiors of pieces with either C Harris Temoku or Nutmeg as liner glazes quite reliably. (I've not tried a lot of other glazes.)  It is critical not to pour or dip the exteriors at the same time, or the body will develop internal blisters from the stresses of wetting and expansion.  A couple hours of drying and/or moisture equalization is definitely beneficial.  I have then gone on to spray the exteriors with multiple glazes, most recently with short periods on a rack in front of a fan between coats.

     The process I'm using is experimental & is derived from what I learned at a Steven Hill workshop.  The most important point of this method is that the glazes don't have to be the high clay content glazes that need to shrink with a clay body starting at the leather hard stage. Click here for an album of B-Mix-5 pots raw glazed with this technique.