PeterH

@Chilly did you have any undercuts?...
PS Comparing fondant moulding with press moulding (probably the the closest pottery equivalent) ...
The fondant process:
— uses a flexible non-absorbent mould
— the fondant sets hard (without shrinking?)
— the set fondant doesn't adhere strongly to the mould?
— fondant sets strongly enough that peeling the flexible mould off undercuts doesn't damage them 

The press moulding process:
— uses a rigid and absorbent mould
— the clay shrinks and becomes harder as it dries
— minimal drying time needed/required
—— the mould absorbs water from the clay; so no air-drying needed and clay-mould adhesion is minimised
—— if the clay dries too much it will shrink-on any texture in the mould
— you cannot cleanly extract the (still fairly soft) casting if there are any undercuts.
So I suspect that you could have issues with
— air-drying the clay
— getting the clay firm enough
— clay shrinkage
— clay-mould adhesion
— the undercuts
PS Using paper-clay would probably strengthen the clay and speed air drying to some extent.
 

You will probably need a "release agent."  For plastic press moulds I use either talcum powder or WD40.  Both will prevent the clay from sticking to the mould.  You might need to remove the clay before it's leather hard, as by then it will start to shrink and can get caught.
I made a whole batch in one two hour class, dusting mould with talc, pressing the clay in, dropping it out, dusting mould with talc................. repeat

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.

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.

What cone/temperature do you fire to?
PS I'm a little confused about the small print in the kiln spec.
Continuously working time on 1240 C (2264): 10 minutes
... and in the manual https://www.technicalsupermarket.com/(EN) RH-16L KILN INSTRUCTION MANUAL.pdf
Using this kiln at temperatures higher than 1,240°C/2,264°F or for longer than 20 minutes at these temperatures may cause problems with heating element(s) and/or with the kiln’s metal  body that are NOT under warranty.
 

What cone/temperature do you fire to?
PS I'm a little confused about the small print in the kiln spec.
Continuously working time on 1240 C (2264): 10 minutes
... and in the manual https://www.technicalsupermarket.com/(EN) RH-16L KILN INSTRUCTION MANUAL.pdf
Using this kiln at temperatures higher than 1,240°C/2,264°F or for longer than 20 minutes at these temperatures may cause problems with heating element(s) and/or with the kiln’s metal  body that are NOT under warranty.
 

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...

Not all rock chicken grit is feldspar.  I got some from another potter that worked, but all the chicken grit (rock kind, not shell) I can find now is granite.  Can add interesting texture but does not melt even up to cone 12. 

A group of potters I belong to used to do a raku firing as a fund raiser.  The members would make items in advance.  We would haul all our equipment out to the site of a local fair and  the public would buy a piece or 2, glaze under instruction of a member.  The pieces would be dried on the lid of one of the 2 kilns we had going and put into the fire when ready.  I don't think we ever had an explosion.  Lin

On very little evidence this might be a grass-ash (rather than a wood-ash).
South Okanagan Grasslands Protected Area
https://bcparks.ca/south-okanagan-grasslands-protected-area/
The Richter Pass has long been a priority for conservation efforts in the Okanagan. The primary role of the South Okanagan Grasslands Protected Area is to protect the dry grasslands and open forests that represent one of the four most endangered ecosystems in Canada.
Glazy has some lawn-ash analyses at https://glazy.org/materials/15037
The materials section at glazy might complement digitalfire's coverage
https://glazy.org/materials?primitive=1
Digitalfire also has
Those Unlabelled Bags and Buckets
https://digitalfire.com/article/those+unlabelled+bags+and+buckets

On very little evidence this might be a grass-ash (rather than a wood-ash).
South Okanagan Grasslands Protected Area
https://bcparks.ca/south-okanagan-grasslands-protected-area/
The Richter Pass has long been a priority for conservation efforts in the Okanagan. The primary role of the South Okanagan Grasslands Protected Area is to protect the dry grasslands and open forests that represent one of the four most endangered ecosystems in Canada.
Glazy has some lawn-ash analyses at https://glazy.org/materials/15037
The materials section at glazy might complement digitalfire's coverage
https://glazy.org/materials?primitive=1
Digitalfire also has
Those Unlabelled Bags and Buckets
https://digitalfire.com/article/those+unlabelled+bags+and+buckets

Hello Ugly Mug, welcome to the Forum.
The video Peter posted does a good job of showing the process. Creating a bed is the best "first step" in the process. Like the video I choose to make a bed using foamcore. (Its cheap and flat and clean.) I use clay to seal the gap between the shape and the foamcore.
Every so often I coat my plywood pouring boxes with Johnson Paste wax. It won't prevent the plaster from sticking but it makes it easier to separate the plaster from the wood if it does. (If the plaster does stick to the wood just tap it with a hammer to dislodge it.)
I don't tap the bucket or the box. I gently create a wave in the plaster mix and let the bubbles rise that way. 
I like to hold a jiffy mixer in my hand and mix plaster that way. Using just my hand doesn't seem to agitate it enough.  

Eye-candy
 

Can you confirm that:
- the controller is "alive"
- it behaved exactly as it did when starting previous firings
- it isn't displaying an error message
Did you hear any relay clicks?
PS
Diagrams at http://coneartkilnsshop.com/index.php/wiring-diagrams/
... are you using 240v?
http://coneartkilnsshop.com//wp-content/uploads/Wiring_Diagrams/pottery/BXGX_1822D_1240rev21Aug23.pdf
http://coneartkilnsshop.com//wp-content/uploads/Wiring_Diagrams/pottery/BXGX_1822D_1208rev21Aug23.pdf

I would put furniture in.
I think it is the clay. Hoping a more fluid glaze will fill the pinholes but might not be enough. Plates are going to be the litmus test as there isn't gravity to help.
 
I have a newer bag of wollastonite that isn't as agglomerated since I wrote that I needed to whiz it in a blender, now I just add an extra little bit extra when I'm weighing out the materials to compensate for what is left in the sieve. My bucket top up batches have 985 grams of wollastonite, so I bump this up to 995 when weighing it out.

A little more detail (and perhaps a picture) would help the experts decide what's the best option for you.
Some suggestions in this thread
 

Eye-candy
 

Eye-candy
 

Ok, now download the firing log and feed that sweet thang into @jay_klay_studio's graphing program to visually see the tracks of the 3 sections. And if you really want to have some fun, add another 9999 drop all the way down to 100 after your regularly programmed cool to log how looooonnnggggg it takes for the last several hundred degrees. Several times over the years I've printed the extended graph of a few kilns as a teachable moment for the students of the virtue of patience, i.e., "Can I get my piece tomorrow?" "No, next Friday."

The circled defects (posted image by OP, above), is the bare clay visible?
Are the other(smaller) spots also defects? ...looks like tiny pits in the glaze.
The circled spots look like what I've called "large particle defect" - where something in the clay was off gassing, something that wasn't burned out in the bisque.
I'd added a hold at 1500°F to the bisque when experimenting with black and dark red clays*; it seemed to help, a lot. One full hour, or half hour on the way up and again on the way down.
Since, I've left the bisque hold, against the occasional "large particle defect" which seems to happen more or less often, depending on the clay...
Running a powered kiln vent - supplying oxygen - should be helping with the burnout*.
Are there more defects where the clay is thicker?
More defects in thicker/heavier pieces?
The blue and green glazes aren't showing any defects? 
 
*credit to Forum member GlazeNerd
 

In case it's of interest-  googling  site:community.ceramicartsdaily.org fibre  soda firing
threw up some hits including
... which includes
In the 90's I decided to do a couple of soda firings in my ancient, Geil, fiber kiln. It sprayed the interior with ITC 100 and after just a couple of firings the old fiber just wouldn't stay put with the ITC. If you're looking for light construction you might try using IFB's, and coating 5 sides of interior bricks with the ITC 100.
 
... which uses fibre as a short-lived sacrificial liner

Elsewhere I found this thread
... which includes this post
 

What color is the cone?

So what turned the kiln off? Did the safety countdown timer turn it off too soon or did the cone melt in the sitter? If the sitter, then check it was not cone 05 instead of 5 (likely), sitter calibration ( that’s a lot of mis calibration, confirm everything else first before drastically recalibrating). You made it to red heat, that’s 1000f + so no stove oven would ever get near there. If all the above is not helpful, then testing the elements is likely next.
The good news, it made it to red heat and something shut it off. First task, what shut it off?

Two googles that might be worth trying, and an example hit from both.
site:glazy.org "standard 266"
https://glazy.org/recipes/22329
Shows a base glaze with several different colourants.

 
"standard 266" glaze selecting the "images" option
https://www.flickr.com/photos/133519868@N03/32484512766

Finally ..
Glazy has an Alfred Blue at https://glazy.org/recipes/217896
... and the referenced "University of Maryland Glazes" article is on p32 of ...
https://ceramicartsnetwork.org/docs/default-source/uploadedfiles/wp-content/uploads/sites/6/2015/06/ceramics-monthly-feb80-cei0280d.pdf
 

Anything of interest in these threads?