Pyewackette

I've been finding bits of sponge in my porcelain, and I thought that was annoying. Now I'm afraid to buy clay ... 

i have given this recipe to members of this forum.  there is a very easy to use red clay made of only 2 ingredients so everyone was  positive it was not good.  someone did the chemistry and discovered it has all it needs.     it is really very plastic, no grog, strong stoneware, pretty red.
try it  50 pounds redart, 50 pounds XX saggar.   water.   makes a lot of great clay.   i no longer use colored clay,  just white.

Thank you for the thoughtful responses! 
I’m using a brown body clay, so I think it may be beneficial to cook off some of the extra organics. I will look at the Duncan thread (thank you @neilestrick !!) I plan to get a pyrometer and start using a cone pack to track my kilns temp throughout a firing more closely.
 
@Hulk  Thank you for the link to the bisque info! 

@Byrd Don't use the search engine on the site.  For some bizarre reason it limits your results to stuff less than 2 years old.  Use google and limit the search to ceramicartsdaily.  Something like
 

Hi  folks, this last week @Pyewackette posted a question in the pool. Even though I think we have covered this sometime this year, it never hurts to approach from a different angle.
@Pyewackette posted:
QoW: What clay body or bodies do you work with and what do you like about it/them? What is the impetus for working with one or multiple clay bodies?  Corollary:  do you make your own clay, and why
My thoughts on this are pretty simple. I use two clays for the last several years, a white clay SC630 that is quite nice to throw and takes my glazes that have used for years quite well. I also use a SC Hazelnut Brown to give me a different set of colors when working. No change in glazes as they look different but darker on the Hazelnut. As far as mixing my own clay. . . not enough space, too much dust, too much mess, more equipment, and too much work! i'll order mine premixed and ready to go!
 
best,
Pres
 

PM me if you want a printable copy of the Mason reference guide. ( I converted it to a pdf for my glaze chem class notebook)

@PyewacketteAll of the oxides in Mason stains are regarded as safe if used in a stable glaze, no different than if said oxides were used as colorants in the typical amounts in a "normal" glaze. The reds and oranges contain cadmium and selenium which would be toxic by themselves, but Mason encapsulates them in zirconium so that they do not leach out of the stain particle. The advantage of using stains to color your glazes is the variety of colors that can be easily achieved without knowing oxide combinations and amounts to add to your base glaze. The disadvantage is cost. As with so many things, you can figure it out yourself the hard way, or you can buy your way out with the gentle application of some folding green.

@ByrdIf the cone bent, then it reached that cone. The potential problem is that it didn't spend enough time at high heat to adequately burn out all the organic matter, which could cause issues with your glazes. If you're using a white clay body, then it'll probably be fine. If you're using a brown body then it's more likely to be an issue.
HERE is a thread with a lot of good information about firing Duncan kilns and how to slow them down. If you use the search bar you'll find several other Duncan threads that may be of use to you.

Do you have a pyrometer to log your kiln progress through firing? 1 cone is not usual practice. A bank of 3 cones one below target cone , target cone and one above the target. A bank of cones on each shelf to see how the inside of  your kiln is behaving.
Good luck.

Hi Byrd,
Welcome to the Forum!
Good question.
Making it through a fast bisque with no damage, that's a win - if the ware went in damp, a quick ramp up past 212°F could be problematic (pro BOOM atic)!
From there, thinner ware should be happier with a short bisque than thicker ware, same for "cleaner" clay, for one of the objectives is to burn out organics/combustibles, which takes longer for thicker ware, and can take longer for "dirtier" clay.
If the wares are thick, if you're using red, brown, or black clay, a more thorough bisque might help - testing will tell, hard to say...
My typical bisque runs about eight hours, however, I'm ramping up to about 200°F the night before, then skipping the initial warm up (to drive off moisture) the next day. I hold at about 1500°F for at least half an hour, which I've found helps burn out stubborn gassy bits, direct kiln vent running throughout - ample oxygen for the burn out.
See second paragraph:
Bisque (digitalfire.com)

@Olivia Try disconnecting two switches at a time and see if it only trips with one of them. A meter won't find the short. You have to isolate it to figure out where it is. However having a meter is good for future repairs.

@Min Wow, ask and ye shall receive!  Thanks for that.  Now all I have to do is figure out which ones are unacceptably (to me) toxic in a liner glaze LOL! Turns out not EVERYTHING can be found on Digital Fire.  Just NEARLY everything.
I've also learned what turned a bowl I glazed a weird mixture of purply-brown and gray. A glaze defect known as Boron Blue.  Some people actually use that glaze on purpose to make that.  I think its hideous.  Now if I could only remember which glaze that was ... Probably I can identify it by the list of ingredients on the outside of the bucket.  Now all I have to do is enter the entire list of glazes into the glaze calculator LOL!

Mason puts out a Reference Chart that lists all the ingredients in each of their stains. 
https://www.masoncolor.com/reference-guide

Hi Pye,
The marking inside the bowl is red slip, added shortly after trimming - whilst the ware is still damp*.
I'd blunged up some red stoneware clay (with the Studio blender, a thrift shop special!) with water, then ran the slurry through the 80 mesh sieve to remove the sand and other bits. A few cups goes a long way.
I've brushed the slip on the outside of wares, using the wheel, then carved design/pattern after the slip had dried some.
On the inside, I've done some stippling, like the one depicted above, dabbing the slip brush as the ware turns on the wheel. After bisque, any lumpy/rough parts sand away easily. Some of the slip "disappears" in the glaze - the effect is muted, somewhat, by the glaze and glaze firing...
Liner glaze, I'd decided, early on, to stay away from metallic colorants, even though there are stable/safe/tested recipes "out there" from trusted sources. For design underneath liner glaze, I believe the slip is ok, and underglaze should be fine as well, also some small droplets of (stable) colored glaze underneath or on top. 
Commitment to utility! Tough, easy to clean, doesn't mark, un-crazed, well behaved (applies well) glaze as a liner.
My liner is clear-ish. Over red, black, or dark brown clay, the Zircopax - at 2%, a translucent white - shows up.
Over white clay, it appears to be clear (but it ain't!).
The Zircopax to lower COE a bit, add some toughness, and reduce bubbles.
Zircopax (digitalfire.com)
Liner Glaze (digitalfire.com)
*but stiff enough to take on some more moisture - from the slip.

@Hulk Just wondering - did you chatter the inside of that bowl?
Also I've been doing a lot of thinking about liner glazes.  I don't want to use any toxic substances AT ALL inside something people are going to be eating out of.  At first I thought I could use Mason stains instead of things like cobalt and chromium and copper, but turns out there's no way to be sure of what they used to make the stains.
But now I'm thinking, after seeing these bowls, maybe in at least some cases (where the clay body is pretty, unlike the old studio clay that turned out the color of zombie skin at anything above bisque) I could just use a clear.  Otherwise I'm good with being limited to white or brown ("safe" colorants) for liner glazes.
Is there any reason a clear glaze couldn't work as a liner glaze?  Do colorants add anything towards cutlery marking and durability?  Anti-crazing?

I fire a top-loader at home and a front-loader at the community centre.  Taking any other factors our of the conversation, for me there are positives and negatives for each.  And all are to do with the shelves.
The top-loader means lowering each shelf down with not much finger space, good posture is needed, straight spread out legs, back bent at the hips.  And it's harder to see that the shelf posts are tall enough.  With the front-loader you have to hold your arms out in front of you with the weight of the shelf trying to do what gravity intends, and you feel like the whole weight is on your fingertips.  Particularly tricky with a full shelf below when you'r trying to maximise the load, and everything is the same height.
I like that with the front-loader I can see into each shelf - even if can't see all the way to the back, so it's easier to move something to gain a little space on a lower shelf at the last minute,  You cannot do that with a top-loader.  I feel the round shelves are more stable on three posts, than the rectangular shelves.  Having one post at the front makes me feel it is less stable. (I don't think it is, it just plays with my head.)
In summary, for me, when loading lots of pots the same height, the front-loader is harder to place the shelf.  If you have a weak back the top-loader is harder.
If you asked me, while loading shelves,  which do I prefer - I'd probably say the other one!
 

About all I fired was tiles. I a 6.5CF square top loader, and a 15.5CF front loader. The easiest method is to calculate your current tile size (in setters?), to come up with the width x length x height. You mentioned upright? ( see below). My top loader has 3” brick, with 1” insulation: extremely energy efficient. Front loaders are the easiest ergonomically, but have more hot and cold spots. When the temp gets into the 1800F plus range: static pressure likes to push the bottom of the door open ever so slightly, which allows cool air into the bottom front of the chamber. Easy to rectify with insulation. The upper rear of the chamber tends to fire hot, which I remedied by drilling a hole from the top; into the rear corner of the chamber. If you fire speciality glaze that is fickle to temperature variations; then a kiln vent would be advisable for a front loader. If the pic I posted resembles what you are doing: then it a simple matter of calculating how many setters wide, by how many setters deep, by how many setters tall: to arrive at a chamber size. Allow 2” of free space around the edges, and calculate space required for shelves and legs. 
Tom

Thought this was a good time (seeing it is American Thanksgiving), to put out a thank you to the potters on this forum who give selflessly of their knowledge and time to help other potters.  Together you have built a great resource and you are very much appreciated.  
 

Hi Dick and all,
I would be willing to do the research and write another article if I can gather enough samples of the latest Custer. Anyone willing to send me some just get in touch.  My best advice is to switch to another spar - g200 EU looks like the best alternative for a potash spar.
Cone 10 bodies were affected when the low P2O3 Custer started shipping around 2000. That resulted in cristobalite production and shivering problems and underfiring in some glazes.
Ron Roy ronroy@ca.inter.net

It seems that the ore body being mined has changed somewhat. I figure that the tile and paint industries are not having problems with the composition so they dont really give a hoot. I have switched all my glazes that contained custer to the G200eu with no problems whatsoever because of how "dirty"...for lack of a better term custer has become. 
 

With the caveat that my kiln does not have a digital controller that would be much more subject to temperature variations, yes, I am proof you can easily run a kiln at 0 C. Mine is in a metal shed outside. The kiln does start to struggle a bit at  -30 C, and at that point I can’t blame it. We don’t get those temperatures for more than a week or so in most years, and they tend to come at times where I can easily wait to fire. The power consumption doesn’t go up measurably: 20*C difference in temperature matters to human comfort, but not to a kiln. 
It’s not uncommon where I live for potters have kilns in their garages, which are typically unheated and are often uninsulated. A digitally controlled kiln will need to have a temperature reading from the thermocouple of 0 C before it will turn on, and what many do will put a small space heater inside the kiln to warm the area before they begin loading. Once the kiln is generating its own heat, it’s usually fine.
Ventillation is another matter. Even with an electric kiln, you will want to make sure it’s vented properly. As the different minerals loose organic components, those carbonates and sulfates will need to go somewhere, and that shouldn’t be into your home, never mind where you sleep. In North America they sell kiln vent kits for the purpose, but you should check with whoever sells you the kiln about locally available equivalents. 
The only time I’ve seen gas kilns indoors was in institutional settings, where the building was purpose built and incorporated a LOT of venting. Otherwise they should be outdoors, but sheltered from the elements. They emit everything an electric kiln does, plus combustion, plus presumably some incomplete combustion for reduction.

I pour outside, finger swipe, spray through stencils. . . weeds, found objects. . . .lace, artificial branches etc, all over textured surfaces that break the glaze even more.
 
best,
Pres

I'm in the process of installing new kiln elements in my old Cress kiln and I've seen previous mentions of doing an empty kiln firing to break-in the new elements. I would guess that @neilestrickwould be the one most appropriate to chime in on the topic of a first-time firing process.
Thanks in advance for your input!

The only reference to density and zinc I could find was a brief mention on digitalfire about there being 2 different processes that can be used to derive zinc oxide, one of which creates a denser product. But the same article mentions that zinc oxide is one of the purest materials we deal with, so I would think that as long as the recipe is using weight and not volume measurements any substitutions would be chemically the same. 
That said, the density may affect other working properties. If the zinc is in the recipe as one flux among several it will matter less than if it’s something like a crystalline glaze.

You’ve ruled out your wedging surface, so that leaves a problem with the clay. If it’s fresh out of the bag, it could be that the batch you have is new clay, and it may resolve in a week or 2. If it doesn’t resolve, contact the manufacturer and see if there are any new materials being used (talc is a recent culprit). It may be a qc issue on their end. 
Frozen clay is a possible issue as well. Some clay bodies benefit from being frozen and thawed, others need to be slurry reclaimed before they can be used again. 
That leads to the last idea I have: If you’re wedging reclaim, are you making sure the fine particles from your throwing slop is going in the bucket with the trimmings and mushed pieces?