Callie Beller Diesel

Just heard this -The owner of Kemper Tools has sold the business. New owner has to move the factory as the property has sold as well. Not sure if this will stay  as a domestic business and what will be made  in terms of the tool line. They made so many I would not be surprized that that line is trimmed down . Pricing may change as well.. It's funny as I noticed Bailey has a sale going on Kemper now which is odd. My guess is there will be a time period that these tools will not be in production as well. The good news is Kemper will be around in some sense in the future. 

@Katie S I have become quite adamant about "what clay is it?"  Name, rank, serial number, when firing for others.  If they do not know, I politely decline.  A friend of mine just had a horrible kiln accident with that very thing.  Melted cups and plates all over the shelves.  Yes, they were low fire.  Fired to mid fire.  The person making the request didn't do their work.  You would probably be fine with 04,  probably.  But.....

Chiming in a little late on this one, but you mentioned the crack in your piece happening at another studio, where the bisque cycle is unknown to you. I strongly suspect the cause wasn’t the fact that it was bisqued twice, more that the cycle used was likely not suitable for your piece. Two foot pieces are going to need a slower cycle than regular pieces, just due to sheer thermal mass.  If the studio’s usual bisque cycle didn’t take that into account, or the kiln pack wasn’t a particularly heavy or even, that would be the most likely explanation to me.
Side note: I just spent the morning going through Ceramic Materials Workshop’s new commercial clay body analysis resource. It’s free if anyone wants to check it out for themselves. So far the submissions are limited to assorted clays in the US that are in the roughly cone 6-10 range. Bill’s statement that clays will shrink upon a second bisque depend greatly on what the first bisque temperature was, and which clay body is in question. If you’re bisquing to a common 06 temperature, the statement of a less than 1% increase is likely enough. If your usual bisque is higher or lower, it might not be. After about 1000*C (roughly cone 04) many clay bodies hold steady for a time before continuing to shrink. If you bisque very low to cone 020, the shrinkage charts actually decrease for a time, meaning the piece expands a bit after the carbonates and chemical water burn off. 
Again, this is VERY clay body dependent. 
 
 
 

Now, to give you a sense of what 'curio' scale means here is the same bisque shown in my hand.  Here I have airbrushed on underglaze in greys and black and I am now dappling him.  Once fired with a clear glaze over this underglaze, he will be a dappled grey!  This is a sales piece that I will be offering at auction probably next weekend while I'm at a live show event.  But for now there's a lot of work to do to him to get him ready to be the new sample of my sculpture in ceramic!  I'll post more photos as I go so you all can see the finished boy when he's done.  I work in many layers, fire a number of times, and will also work in over glazes.  The upright mane ribbons will be added later after he's completed and are going to be enameled metal but I haven't finished making them yet.  They each fit down into little  holes I have drilled down his neck.
I am also making mold pieces for a larger 'traditional' scale version of this boy that stands about 8 inches tall.  I hope to have that one casting by June in time for a huge international event I'm attending in July at the Kentucky Horse Park in Lexington, KY.

This is Porths, my first version of this sculpture I started way back about 2007, almost completed in 2009 before illness derailed my studio for a while.  At any rate, I FINALLY finished this boy last year and released him in a resin edition.  I've since gone on to do a 'hairy' Pasture Porthos who's a bit chunkier, and with more feather, thicker legs, long mane and swishy Fabio tail who's casting in a resin edition this year.
Anyway, I've been busting butt to make MOLDS for these two versions of my Porthos sculpture.  Currently I am having the hairy Pasture Porthos molded and cast in England in fine bone china, though I'm also about to start testing slip and settlers for fine bone china pieces here in my studio later this year.  Meanwhile I'm focusing first on using finely ball milled earthenware with talc to cast some pieces.  This first one I've molded right here in studio is what we call Curio scale, a large mini in size.  He's my test cast to see if my mold worked (it did first try!) and to help me figure out how I want to rework and clean up my mold pieces to work even better.  Then I'll be making rubber molds starting next week of each plaster mold piece so I'll have a master from which to cast as many plaster replacement molds as I ever will want, later.
So here's my first ceramic bisque of Porthos with his original docked tail version (mane flights to be added later), an American Percheron with tail bows.

two layers of 1/2” Hardibacker board will give you some peace. No mixing plaster, woohoo! Great to wedge on, dimensionally satble, easy to get. I still use it for wedging and working surfaces, as well as ware boards. Pulls water out aggressively. It will saturate eventually, the same issue happens to terra cotta planter plates which I also use for small batches. Of course it happens with plaster too, 

This. 100000X this. If your clay body is giving pinholes of some kind with several glazes, it’s the clay body, not the glaze or the assorted firing cycles. It may well be that an ingredient in the Laguna body just doesn’t want to play nice, whatever is done with it. You have to weigh wether you like using this clay more than you want a perfectly defect free surface.
If you need a good red clay/white glaze combo, M390 and Ravenscrag slip 80/20  with frit 3134, and 2 opacifiers of your choice. (I recommend a tin and zircopax combo if you don’t want any titanium variegation). Reasoning: they give different qualities of white. Tin by itself is very soft, and can be grey-ish or even drift towards a violet in certain light when used on M390 in particular. It’s also expensive. Zircopax by itself is very stark, and gives a very “bathroom fixture” white that resists breaking or pooling. The 2 together give a soft white without weird tonal casts, gives a little more visual interest and offsets the end price of the glaze. I use a max of 10% opacifier, but judging from the look of your photos, you might want a slightly more translucent version, so you could see what happens with 7 or 8%. 
I fire with a very analog kiln at home, so I can’t give specific numbers on ramps and speed. I slow my kiln down around the carbon burnout stages mentioned in the Steve Davis article, and I judge that through the colour of the kiln. I’ve recently started working at a place that has brand new Bartlett 2 touchscreens though. I feel spoiled! They are to be preferred over my methods.
I think speed of bisque is more important than end temperature, so slow through the appropriate zones. I think the Naomi Clement one is a bit of overkill.  The 12-14 hours of Davis’s cycle (assuming no drying soak at the beginning) is plenty long. Note the pauses around 1500F that both Clement and Hulk have suggested.
The glaze cycle I use to get what is effectively cone 7 is a drop and hold, similar to what you’ve already worked out. I go to cone 6 with a 20 minute hold after the drop.
Note that there will be upcoming changes to M390: according to my supplier, Plainsman demand has gone through the roof lately, and they’re struggling to keep up. They have one clay mixer that they have to cycle all their different clay bodies through from lightest to darkest. While another one has been ordered, it’s not expected in until next year. In the meantime, they’ve made the decision to remove the 80 mesh sieve from the machinery in order to get the clay to go through faster. This will affect M390’s texture starting this year. So we’ll all have to revise some porosity testing until they get the new machinery in place.
 
The last suggestion I would have is another bisque cycle. But this time, only go to 010. There have been a few reliable potters in various internet spaces lately speaking about this (For Flux Sake podcast in particular). I believe the argument is that the application a more porous clay body gives a dipped glaze results in fewer defects. I haven’t experimented with this personally though, so that one is a shot in the dark if nothing else works.

This. 100000X this. If your clay body is giving pinholes of some kind with several glazes, it’s the clay body, not the glaze or the assorted firing cycles. It may well be that an ingredient in the Laguna body just doesn’t want to play nice, whatever is done with it. You have to weigh wether you like using this clay more than you want a perfectly defect free surface.
If you need a good red clay/white glaze combo, M390 and Ravenscrag slip 80/20  with frit 3134, and 2 opacifiers of your choice. (I recommend a tin and zircopax combo if you don’t want any titanium variegation). Reasoning: they give different qualities of white. Tin by itself is very soft, and can be grey-ish or even drift towards a violet in certain light when used on M390 in particular. It’s also expensive. Zircopax by itself is very stark, and gives a very “bathroom fixture” white that resists breaking or pooling. The 2 together give a soft white without weird tonal casts, gives a little more visual interest and offsets the end price of the glaze. I use a max of 10% opacifier, but judging from the look of your photos, you might want a slightly more translucent version, so you could see what happens with 7 or 8%. 
I fire with a very analog kiln at home, so I can’t give specific numbers on ramps and speed. I slow my kiln down around the carbon burnout stages mentioned in the Steve Davis article, and I judge that through the colour of the kiln. I’ve recently started working at a place that has brand new Bartlett 2 touchscreens though. I feel spoiled! They are to be preferred over my methods.
I think speed of bisque is more important than end temperature, so slow through the appropriate zones. I think the Naomi Clement one is a bit of overkill.  The 12-14 hours of Davis’s cycle (assuming no drying soak at the beginning) is plenty long. Note the pauses around 1500F that both Clement and Hulk have suggested.
The glaze cycle I use to get what is effectively cone 7 is a drop and hold, similar to what you’ve already worked out. I go to cone 6 with a 20 minute hold after the drop.
Note that there will be upcoming changes to M390: according to my supplier, Plainsman demand has gone through the roof lately, and they’re struggling to keep up. They have one clay mixer that they have to cycle all their different clay bodies through from lightest to darkest. While another one has been ordered, it’s not expected in until next year. In the meantime, they’ve made the decision to remove the 80 mesh sieve from the machinery in order to get the clay to go through faster. This will affect M390’s texture starting this year. So we’ll all have to revise some porosity testing until they get the new machinery in place.
 
The last suggestion I would have is another bisque cycle. But this time, only go to 010. There have been a few reliable potters in various internet spaces lately speaking about this (For Flux Sake podcast in particular). I believe the argument is that the application a more porous clay body gives a dipped glaze results in fewer defects. I haven’t experimented with this personally though, so that one is a shot in the dark if nothing else works.

Tagging @Callie Beller Diesel on this in case I'm misremembering but I believe she fires 390 to cone 7 for absorption reasons.

Be sure to carefully check for application defects!
This may be what was nagging at my memory?
During yesterday's glaze session, while checking for tiny bubble marks and pinholes, an "ooh yeaa" moment:
microtips - Studio Operations and Making Work - Ceramic Arts Daily Community
Where any air can be trapped in the clay, or at the edge of applied underglaze, or at the edge of wax resist, et cetera, as the glaze dries, then the bubble pops - there's a pinhole!
I'm checking the glaze layers more carefully than ever!
 

Well it's looking like the second quarter in terms of Pottery sales has been slow-same as the first quarter. This is showing in my retail/wholesale outlets . The economy in our small backwater community is always lagging behind the national scene . Its been a bust and boom economy localy for all my time living here. This area was once king to Redwood timberr sales (when I moved here over 53 years ago). Then that went bust and Weed growing took over until thats gone bust in past years. Now its in between  the next thing. The toursit industry has been steady thru it all and thats a season flow for te shops and galleries . Now that I no longer travel with pots out of the area so I'm  now subject once again to this cycle except to one very large wholesale gallery far away from here wich I'm working on a huge twice a year order right now. In terms of my slowing down work wise this actually has worked well for me..I need to stock up for the summer trade season soon aas well. Not sure about te rest of the country but here pottery sales are slower than past years at this time locally.

If the food colouring is just to tint the raw slip then I would suggest using paste food colouring rather than the liquid, it goes much further.

A waster slab should do the trick, or put some silica sand on the shelf. Make sure you put kiln wash or alumina wax on the waster slab so the tile doesn't stick to it. If you need a cooling ramp it would be during quartz inversion, so from about 1100 to 900, but it's rare that you would need that.

I used the cones and they bent as per the temperatures. But I am going to run few tests and also maybe aad a new program because I am also having issues with pinholes lately. Thank you!

Claybodies should be vitrified enough to not weep / leak even with no glaze on them when used for functional work and fired to mid or highfire.
Is this the clay you used? https://tuckers-pottery-supplies-inc.shoplightspeed.com/mid-smooth-stone-speck-clay-cone-6-stoneware-ecom.html
If that is the clay then in theory the clay should be vitrified enough to not leak with a posted absorption figure of 1.0 % but published figures can vary by +/- 1%. I would suggest running your own absorption tests. This is a good idea to to when using a new clay or every once in a while on an existing clay as materials can change.
How to on testing for absorption here if you need it, about 2/3 the way down the page, I would suggest doing the weight calculation test with several samples placed in different areas of the kiln. 

If she isn’t absolutely 110% sure it’s a cone 10 clay then I would pass on this. 
This makes sense to fire the clay to maturity / cone 10 if she doesn’t plan on glazing it and it is indeed a cone 10 clay. She might want to leave it as bare clay or be planning on doing a cold finish on it. Firing to maturity would be a clearer way to describe what she wants rather than calling it a bisque firing. A mature body is far stronger than a bisque fired body.

An relevance? https://www.lickinflames.com/obvara_june_2021.html
Generally speaking, the hotter the pot going into the mixture, the darker it will be. Nearly glossy black pots are from the hotter side of the firing range and tan pots are usually from the cooler side of the range. Really hot pots held in the mixture longer will yield fewer patterns. Cooler pots held in the mixture longer will possibly not carbonize as they cool below the threshold where carbonizing can take place.

What type of kiln is it? If it has a door, just pull the obvara and then close it up and finish the raku pieces. Otherwise I think you'd probably be fine just firing up to raku temps and pulling the raku pieces first while the obvara cools a bit. It's not an exact temperature anyway, since the pieces cools some between the kiln and the bucket, and the last piece is always a lot cooler than the first.

Another tip would be to leave a “button” in the center bottom of the plate. You can find some images of Steven hills plates/platters to get the idea. 

Couple of areas where clay can be sensitive to fast heating, also slow at start, or even candling if you not sure of moisture content  and clay thickness. Some folk hold somewhere around 700-800 °C to drive off xhemically bound water but if you havent had to up until now, I wouldn't start.
Let's know how you go,centainly save on energy and time.

I believe that recommendation is to prevent the material from getting into the element grooves. I don't think that switching to another material is necessarily any better in that regard. If you're going to do it, use the material that works the best which would be silica sand, and just be sure not to get any into your elements, and vacuum them out after firing.
There is very little shrinkage in a bisque firing, so it's more about even heating/cooling and/or expansion/contraction during the heating/cooling.

Slow. Both for firing up and cooling down.
These pictures are from Digitalfire of lowfire ware, pots have cracked from uneven cooling, edges will have cooled faster than the middle area of the pieces. The way to avoid this is to have the cooling down go as evenly as possible. Slow the cooling down between 1150F - 950F, I go at 100F/hour through this zone with suspect work.

 There is negligible shrinkage, ie less than 1% between bone dry greenware and bisque firing to ^06- ^04, would be interesting to see data that shows refiring to a lower temp causes more shrinkage.
edit: when having your piece in the kiln put it between shelves, not at the top or bottom of the kiln, this helps the heat even out also. I put rectangular or triangular kiln posts around the outside edge of the shelf also. (round posts can roll)
 

Hi and welcome!
Just to clarify, do you want it to look different in the bucket, or in the end result?
If you want it to look different in the bucket, food colouring works a treat, and burns out.
If you want the end result to look different, a small quantity of a light blue stain would pop glaze colours better than a brown or grey one would.

Hi and welcome! I wish it was under better circumstances.
The pictures are worth a thousand words, and thank you so much for including those!
The fact that the piece is broken so cleanly, and in 2 near-perfect vertical lines all the way through means that this wasn’t specifically your clay, or anything you did during building the piece. It’s a nice dense clay  that probably stuck to the kiln shelf due to the mass and size of the piece, and cracked during cooling. For the next pieces, I’d fire them on some sand/alumina so that the piece has the equivalent of little refractory ball bearings to shift around on. You could also use a waster slab that will shrink at the same rate as the piece, but take the brunt of the force and absorb the crack instead.
If the clay survived the bisque just fine, another possibility is to not fire the piece to full clay maturity. Porosity in the end piece is less of a concern for you than it would be for someone throwing functional ware.

Interesting point. Our raku glazes do best at 1850 or maybe even a bit hotter than that. I typically judge by the look and not so much by the pyrometer, so maybe I can judge the color for obvara...