neilestrick

The cone you fire to doesn't really make a difference, because things start burning out as low as 500F degrees and is pretty well complete by 1900F degrees. Bare minimum you want a fan in the window pulling air out, and sufficient makeup air. If you find that doesn't work, then I recommend getting a downdraft kiln vent.

Finally got the new belts and it was definitely the issue! I read that you can still throw with broken belts but it was messing me up big time so I don’t recommend. 

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.

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.

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.

I think maybe you're working too slowly. It should only take a minute max to sift the plaster into the water, another minute at most to gently hand mix. Then lit it sit for a couple of minutes and then power mix.

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.

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.

There are always exceptions to the rule, but I would not recommend trying that again. Glad it worked out for you!

Those shrinkage rates are more than close enough for what you're doing, and those numbers are way too precise. There will always be slight differences in shrinkage depending on the  accuracy of the firing, the thickness of the pieces, etc, so for them to give a number that precise is totally unnecessary. They basically have the same shrinkage rate.

Take off the bottom cover and see if the belt came off or broke. 

Thank you for answering. The kiln is very basic, no kiln sitter, just the controller shown in the attached phot. I changed the fuse which has fixed it, but I don't know why the fuse would have blown - maybe it was just old. I waited until it had cooled and had a look inside - everything looks ok, just half-fired! I have now turned it on again and will just watch to see if it happens again.
Julie
 
 

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.

It lets you copy, you need to go till the last screen to get into temperatures to get that option.

Dunno, I don't have a Skutt Touchscreen, and the "user manual" is a help screen embedded in the controller. All I know is what I hear from others who are struggling with it.

Those shrinkage rates are more than close enough for what you're doing, and those numbers are way too precise. There will always be slight differences in shrinkage depending on the  accuracy of the firing, the thickness of the pieces, etc, so for them to give a number that precise is totally unnecessary. They basically have the same shrinkage rate.

Im so excited for the kiln that i didn’t even check mains fuse before posting this question 
found one fuse blowin, I’ll replace and i hope its will work this time
 

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.

Unless you make it considerably thicker, porcelain is going to warp with a form like that. 

Unless you make it considerably thicker, porcelain is going to warp with a form like that. 

@Bill Kielb @neilestrick
Thank you so much!!  
Bill I’m so impressed and grateful for the time and energy you took to help me out! I have been trying to fix this since last year when I received the kiln but nobody had a clue …and in just one day you fixed it!!!  It took a long time and effort for me to get a kiln and I was devastated  because I couldn’t use it.  I can’t express how happy and relieved I feel!! God bless you!! After all this time,  I am about to finish my first glaze firing with the temporary set up, the kiln is cooling now and everything is going great! 

I will follow the advice and update with pictures and results so more people like me can find this post in the future and fix similar issues easily. 
This is a great community and you guys are amazing, thank you so much! 

Computer fans work great for this application. There's already a grill in place on the box, so measure that and get a fan that fits. This is a small enough box that the output of the fan won't matter. Amazon carries a bunch for very low prices.

Is there a fan on the outside of the case that we can't see in the photos? Definitely need a fan to keep the SSR cool.

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?

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?