[Glazed pieces hung out at 800F degrees - ok?]

Thank you! Based on the error message, it might be the relays which we are checking now, or it the kiln was loaded way too bottom heavy.  Elements are all good thankfully. 

Once we get that sorted we will just give it another go  - I had just wondered if I needed to reglaze or fire differently the second time since the pieces already fired at 800 degrees for awhile, but I am just overthinking it.

[Glazed pieces hung out at 800F degrees - ok?]

The kiln gods frowned on me last night. My Cone 6 glaze firing errored out and the kiln only got up to 828F degrees before stopping and cooling back down. 

The pieces look fine - like unfired glazed pieces but the surface looks a little "cooked" or "toasted".  Good to just fix the kiln and give it another go? Or did something happen chemistry wise to the glaze hanging out at 800F that I should take note of before refiring?

Thanks in advance!

[Crack Diagnosis?]

1 hour ago, Babs said:

How are you drying this multi layered slab?

What is your firing schedule?

Had a teacher who said many times, to non listening teenagers, " It is not the material but the operator", i.e. the process, design etc being applied so before troting down to the store, check your steps, or it could be Murphy....

Happening all over your kiln?

 

Happening all over the kiln: in a word yes. We are getting massive dunting cracks (or more accurately gaping fissures of doom) in work that is larger scale hand built lamps using same B mix. We have tried everything - slow drying, slow firing schedule, glazing insides, etc all to no avail so perhaps perhaps we are the common denominator and not the clay. Pic attached of example of these pieces that we salvaged through repairing the cracks in the end but it’s rare we get one without cracks completely. I figured it was the B mix clay given how widely different these two designs (the flat slab light versus these big organic coil pieces) are and each are having problems but perhaps not. 

[Crack Diagnosis?]

1 hour ago, Mark C. said:

I think B mix is the wrong clay for this. It does not slab well (staying flat) like to cracks as well and drys super uneven.

I work in porcelain 95% when I need to do slab work I choose other white  bodies

I make larger press molded baking dishes -that body is white -its 1/2 porcealin and 1/2 wso called 1/2 and 1/2 the WC number is 382. Its made for slab torture.

I suggest a body thats more up to the task any white boidy with finer white grog will work as well.

This was what I was worried would be the ultimate answer. I say that because we really want to use our low fire glaze and also have the clay fire to a buff color, not white. 

[Crack Diagnosis?]

1 minute ago, PeterH said:

How do you support the pieces when firing; flat on the shelf, on a waster, on sand, ...?

Flat with sand and right side up, meaning the back with the "walls" is on the shelf.

[Crack Diagnosis?]

4 minutes ago, Pres said:

Another thought is the construction process:  cast?, press mold? 

 

best,

Pres

Meaning is it or meaning it should be? These are hand formed out of slabs. 

[Crack Diagnosis?]

Here are some pics of another similar piece with post bisque firing crack that runs on the front and then continuously up the back (I marked alongside in yellow so you can see better) 

Just the wrong clay for the job perhaps?

[Crack Diagnosis?]

Those spirals, wow, interesting how you can really see them there. We like the crazing and the reason we are under firing is because we like the color of this clear low fire glaze paired with the creamy color of the B mix. And the B mix is just always available. We did order some with grog to test out, still waiting for it. 
 

Definitely not a toilet seat lol. It’s a wall sconce or will be. It’s about about 12 inches in length and only sits off the all about an inch. The back side “walls” are for hiding LEDs/horse hair - see pic. Those walls are slab strips cut and attached to the back.  Here is pic of similar sized finished piece. Our success rate (I.e. no cracks) has been dismal with these pieces. They either crack like this or have hairline cracks after bisque. 

[Crack Diagnosis?]

We are doing a ramp up and down during firing - we have other work that is for sure cracking due to dunting so we added a ramp down on everything. 
 

I will check if the glaze edge is rounded over when back in the studio tomorrow. We certainly have other pieces that are just like this in design - large flat wall hanging pieces - that are coming out of bisque with hair line fractures. This particular piece didn’t appear to have any cracks after bisque though. 

We are not wedging this kind of flat slab work out of the bag. That is interesting to think about.  
 

One thought I had was if it was somehow due to the clay being high fire and the glaze being low fire and the mismatch of that. The clay is thus being under fired. Also B mix might just not be the best choice for large flat surfaces? 

Okay! Back to tearing my hair out!

[Crack Diagnosis?]

Is there a doctor in the house? (Wish my first post was not about cracks!)

The details: B Mix with clear glaze, no cracks after bisque on this particular piece, happened after glaze firing. However, other similar pieces in design have come out of bisque with hair line fractures. There was plenty of drying time and no visible cracking while drying with any of the pieces.

Any ideas?