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Could be the horse kicking the bowl? Just a thought ok kidding aside the waster slab is the best dry alumina  second best all other coatings are lesser in my mind  that said better

Thanks Bill, think I will order some tomorrow and maybe Kaolin ep and Kaolin calcined to make my own kiln wash as well.  

For wash use Alumina Hydrate I have used the below for many decades -it costly to make but works better than lesser washes . the best kiln wash mix I and. few other potters  feel is 50

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I have learned long ago that quaility matters especially with plumbing goods. Moen-Kolher etc-I kept a set around of each  just for the measurements for my customers sinks.Of couse I had a friend in the business so the cost was low-still have them in boxes-maybe furure yard sale items

Everbuilt? never heard of them

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I have had the vent all along and shut it off when the elements are done heating. Wonder if the kiln shelf has anything to do with being a heat sink on a large piece. Maybe I will try butting my waster on some 1/4 clay coils that I have used for larger items. I was putting the sinks on them before my last try.

 

 

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32 minutes ago, ronfire said:

Wonder if the kiln shelf has anything to do with being a heat sink on a large piece.

Highly doubtful as the shelf has so much thermal mass it would slow the rate of cooling ......... for the entire kiln that is. Old  thick shelves in a firing  Can be a significant portion of the total mass. That means they heat slow and they cool slow Taking time to remove the stored heat. If your ware is in contact with them, they provide nice even heating and cooling by conduction. Late in the firing (red heat) it’s radiation, conduction and almost no convection. The air inside is far too thin to hold any significant heat. Now a steady breeze of cold air - different story. Most kilns have little air movement, even with a properly installed vent.

Edited by Bill Kielb
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Well just removed another sink from the kiln, this time it was with the old glaze. I had about a 3/4 gallon left so I had to pour it on instead of a dip. This sink was good with no hairline glaze cracks. The good news is there is 1 more bag of the glaze available and I have it on order. Don't know what I will do after it is gone as some of the ingredients are hard to get.

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@ronfire, first off I'm glad you had a successful sink firing, must have been a relief! 

Couple thoughts, on my earlier post I did wonder about the expansion of the replacement glaze as it was made for M370 which is a lower expansion clay than the M340 you use but then I found a page from Digitalfire where they were recommending it for M340 so I thought I was wrong. Hopefully the successful firing is the way things will continue but I'ld let Plainsman know about your possible dunting cracked sinks with the G2926B, would be interesting to hear what they have to say and if they have run dunting tests with it. 

 

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Min, I have been in contact with Plainsman about the problem I have been having and this was their reply.

 

"These are heavy pieces with a big foot ring. That means significant variation in thickness across the cross section. The hole in the middle also provides a point of crack initiation at the center of the section most likely to have a temperature difference to the edges.

In electric kilns it is extremely difficult to keep an even temperature across a piece, both on heat up and cool down. Gradients created on heat up can survive to cool down also.
 
The pieces seem too thick to be affected by any thermal expansion compression that might be created by the glaze. In fact, the G2926B has a lower expansion that G2916F, that means it should be under less compression.
 
If you are not in a hurry on the firings it seems that it might be best to slow-cool them. I would recommend starting with 50F/Hr. That will mean a 40 hour cool. The most likely place where the dunting is happening is around 1000F, so you could slow cool from about 1300-700 if you are willing to risk more pieces."
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34 minutes ago, ronfire said:

In fact, the G2926B has a lower expansion that G2916F, that means it should be under less compression

Are these measured COE or calculated? Anyway just curious, and since you had success, maybe you want to replicate exactly what you did this past successful firing. Compress around hole, Alumina, your firing schedule, same glaze. Just saying to see if you can get another successful one out. Then maybe change only one thing at a time to find the main cause.

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  • 2 weeks later...

Here is the bottom of my personal sink in one of our baths. It has no overflow but if it did it would still look like this. The sink has been in use since 1983. The hardware is Brass duck bill (like you seen medical facility -made by Chicago Faucet -at one time a high end faucet.

The sink has thrown foot and a inner slump ring-stoneware fired to cone 10 reduction. That collar is for the gap in threads -its siliconed to bottom of sink and is proud of foot. it would hold the overflow tube if I made one as it would be a flexible plastic pipe that plugs into that collar for overflows from a few side holes in top and a clay clam shell that hs a small tube connection near rim.I mnostlu made this type of sinks.I amde maching cly handles for high end hardware as well so the facet handles mactched the sink glaze.Long in my past as a potter.

I made a lot of these back in the day never had much cracking issues-they are thicker than regular pots (and should be for a sink)They last a long time.

 

IMG_3514.jpeg

Edited by Mark C.
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