Rae Reich

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.

Yes, but it may introduce more problems than it solves.
To my untutored eye it looks like firing with a sitter would probably solve your slumping issues.

... but would introduce glazing issues.
The classic bone china solution uses a supported high-fire bisque and an unsupported lower-fire glaze, which creates its own problems.
Bone China https://digitalfire.com/glossary/bone+china
The process is completely different than what a potter would do: Bisque fire, glaze, high fire. Bone china is bisque fired to high fire and then glazed at a very low temperature. Since the porcelain has zero porosity, getting a glaze to stick and dry on it is not easy, the process needed goes well beyond what a normal potter would be willing to do.
PS
Balancing slumping and decoration has a long history. Robert Tichane expressed his surprise when he finally realised that the ancient Chinese cup he regularly drank from had a guilded rim to disguise the lack of glaze on the rim (a result of firing the cup rim-down to minimise slumping). 
I'm having difficulty visualising your "handmade leather molds". I assume that they are semi-flexible press-moulds, but am unsure how you extract the bowl from the mould.

A thicker rim will hold its shape better, if you can work that into the design/construction.
Q: is it strictly necessary to have a perfectly round rim? The intriguing soft appearance of your sculpture does not, to me, require a perfectly circular rim.

The concave then convex side design might also be contributing to it being pulled out of round. 

Sponges, chamois, plastic, all sorts of tools over the years in our ceramics lab recycle in college. Those chamois really disguise themselves!
In commercial clay, a supplier, who was gradually going out of business, ran their rusting pug mill to the bitter end. We found chunks of rusty pugger in nearly every bag. No major injuries, but a challenge to throw. I was able to complete an 8” vase while leaving a 1/2” square of pugger in the wall, about halfway up, even while ribbing it out (carefully) as much as possible. We were curious about how it would fire. The fragment melted out and left a trail of mostly iron down the side beneath a tidy hole. ;p
That Franklin Adams clay was really nice and a dream to throw, even so.

A thicker rim will hold its shape better, if you can work that into the design/construction.
Q: is it strictly necessary to have a perfectly round rim? The intriguing soft appearance of your sculpture does not, to me, require a perfectly circular rim.

Many years ago, one of the students in the college class lost the bottom nut from the extruder die holder while cleaning it in the cleanup bucket in the sink. Irritating, but not the end of the world to have to go to the hardware store for a replacement nut. We periodically scoop the sludge from the cleanup bucket into the main recycle barrel, and when that barrel is full, I pug the recycle in to a proprietary mix that is so proprietary that even I don't know what I put in the pugged clay logs. Despite the unknown mix, it's usually nice enough to work with for class demos and experimental practice work. About a year and a half later, I was making a batch of Empty Bowls, and felt a lump in the wall of the cylinder. Thinking it to be an air bubble, I poked it with my needle tool, but it was a hard chunk. So I dug it out, and there was the long lost nut.

New clay =Rocks/stones/ sticks and cat poop/small metal bits
My recycle -small stones and grass

Hi folks,  I was helping in the Ceramics for Adults class today at the HS I used to teach in. I had taken my wedding room off as I always do to work during the 3 hr class. I noticed someone else had taken off her engagement/wedding rings the same and set them on the table. I kindly admonished her for being careless and told her about a student of mine who had accused an entire class of stealing her engagement ring she had just gotten last weekend. We went through all sorts of investigations, questioning, and a very distraught student and class over the loss. The ring was never found until several years later I heard a grinding sound in the Walker Pug mill. Taking off the top cover of the auger tube revealed after so search a mangled gold ring setting without a stone. We searched everything, and still did not find the stone. but lots of clay had been pugged out of and old barrel mixed with newer slop. What a surprise .
I also remember when in college finding parts of a metal kidney rib in the clay while wedging it. . . cut me up!
QotW: What surprise have you found in your clay, either fresh or recycled?
 
best, 
Pres

Hi everyone!
I have been struggling with warping rims on my porcelain pieces. I was wondering if you could give me some advice on this matter. To provide some context, I make porcelain pieces using handmade leather molds. The challenge I am facing is keeping the rim in a circular shape, as it warps during the glaze firing process. I am considering firing the pieces at cone 6 to minimize the warping. However, I am also concerned that firing them upside down could cause the body's weight to bend the walls. 
 
 Do you have any suggestions or methods I could use to avoid this issue?

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.

So I’m going to preface this by saying I’ve never fired Obvara, and I’ve only ever fired raku by eyeball, never with cones or thermocouple. (Please do this with proper eye protection). So I couldn’t tell you what temperature exactly I was using, but the glaze recipes used were mostly gerstley borate at the time, and that melts between 1550 and 1600 F. 
So my question is, can you fire the raku pieces to a lower temp to match the Obvara recommendations, or are you using glazes that really don’t mature until that hotter temp?
If you do need the hotter temp for raku, it’s possible to roughly judge the temp of a piece by the colour of the glow coming off it.  The  chart linked below has a nice colour gradient illustration, and you can do a bit of a comparison from there. There’s a paywall, but you can use one of your 3 free articles/month to view it. 
https://ceramicartsnetwork.org/ceramic-recipes/recipe/Kiln-Firing-Chart-142658

I don’t mind making mistakes because that’s where you learn, but man is it frustrating when the changes don’t help! (Especially when you have people waiting on you.) I haven’t notice any kind of change in sound with the wheel which is why I assumed it was my doing even though my throwing was fine till it suddenly wasn’t.  I just ordered the new belts so hopefully they’re in soon and I can give you an update. Thank you for responding and the reassurance! There is always room for improvement, indeed!  

Good question!
I'm in my seventh year of throwing*.
The sessions when most (or all) goes into the recycle bin (else dried a bit and then wedged up to re-throw) still occur - not as often tho'.
The belts slipping could be throwing your throwing off!
While waiting for your new belts, can you tell if there's slippage?
The motor noise changes as you throttle the pedal - does the sound change without throttling? ...as drag on the wheel increases, does the motor rev?
Hope it turns around for you, please do post updates.
 
*At a hobby level, serious hobby, but not anything like full time.
There's still improvement! Just recently I feel, think, and believe that I'm almost back where I was before injury and moving put a hold on my progress.
There's plenty of room for improvements...

I first got hooked on clay because we did raku at my high school. The only time we had anything explode was the one time we tried firing a piece that wasn’t bisqued first. 

I’ve seen this form a bunch, and yeah, it’s tricky to get right. One solution for the warping I saw another potter online do was to do all the minimal trimming and cleanup as you describe, but they then added a slip trailed circle of clay as a foot rim. It was just enough to keep the full surface of the plate’s bottom from being in direct contact with the kiln shelf so you don’t get the warping, but still keeps the same aesthetic qualities of this style.
Results may vary with different clay bodies, but it’s something that’s worth a shot.

I'm seeing a lot of plates made like this these days, it's a good way to make a plate with this type of design. I've got one bisque fired as a test but haven't got it glazed yet, it was really fast to make and I also like that it doesn't require any trimming. That nearly vertical edge is going to help prevent sagging/warping during the glaze fire compared to a flatter more horizontal rim.
I would suggest putting one of yours in a glaze firing with no glaze on it, if it doesn't warp then it would suggest the glaze fit could be the problem.
Welcome to the Forum.

I make square slab plates on a plaster slump molds . they are not footed (no coils added). They pop off the plaster well and have a curve to them which lessens in the glazze fire. They have a square area that is flat in about 1/3 of the form with the lip angled up. I have to sizes and have way better luck with the smaller 8-9 inch than the larger 14-12 inch which loves to lay down to much in a glaze fire

Not everyone wants to or is able to throw dinner plates on the wheel. I slab build my plates, and it is much faster than throwing and I don't have problems with humping in the middle.
@chris123 I think the issue is either with glaze tension as mentioned above, or it could be from uneven heating/cooling between the edges and the center or the top and bottom.
1. Does it happen with all of your glazes or just one?
2. What size kiln do you have, and what firing schedule are you using?

Tried this years ago, and found it was indeed easier to just throw them. I tried mine throwing the flattened slab on a plaster form with a flat bottom and the sides shaped for a plate. while shaping it I threw the foot ring. Alas 2-3 out of 10 would warp. I decided it was because of the shaping of the form while on the wheel would cause particles to become circular in motion as opposed to the center being non aligned from the rolling out. Just my thinking at the time, but now I throw much faster plates using large slightly curved ribs.
best,
Pres

For me throwing the whokle thing on the wheel is faster by far. The time is trimming a foot.The wares are solid and do not warp. The compression is good and no memory issues with the clay .

For me it would be faster to just throw the plates on the wheel from the start rather than using the slab roller.   However, I do find that a foot ring adds stability to plates during firing.  Have you considered using a slump mold instead of throwing the slabs?

Hi Mia00,
Welcome to the Forum!
I'm not finding anything on Email pottery wheels in general, let alone the particular Type and Catalog spec (which I'm not able to read) stamped on your ID plate.
If the motor, speed controls, drive mechanism (are there pulleys and belt(s)?), wheel head shaft, bearings, et cetera, are in good shape (else can be refurbished/repaired), perhaps you can use the damaged/swollen parts as templates for replacements?
Email Industries in New Zealand was involved with metals (particularly pipeline and plating), appliances, building and industrial products, and more ...interesting! The "Email" moniker is/was an acronym of Electric Meter and Allied Industries, coined in 1951, well before widespread use of Electronic Mail.
Email sold items branded Westinghouse, Kelvinator, Simpson, Chef (and others) under license from overseas companies...

When pulling mugs or cups or any cylindrical piece off of the hump make a pancake larger than the defined bottom of the piece then draw up the sides to form the walls of the pot. This keeps the alignment of clay particles even as opposed to pulling the walls up as in a normal piece thrown off of the wheel head or bat. The difference is that you are unable to compress the floor of the pot sufficiently off the hump leading to unaligned particles where the wall meets the floor,
 
best,
Pres

Test tiles didn't work out but I have another slip  idea  rattling around in my head.  I decided to take a break and make new address plagues for my mailbox,   I made the original ones 5 years ago but someone decide to break them up with a tire iron.   I had made a press mold for the plague so the only thing that will require some skill is the decorative glaze work.  Living on a rural road you have teenagers drive by mailboxes and hit them with a baseball bat or run over them.    Denice