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5 minutes ago, ronfire said:

I made up some kiln wash today on fresh cleaned bare shelves. I am getting lumps from or thick type runs when I apply with the roller. Seams the shelves suddenly grab the water out of the mix and harden the wash.Think I will now have to lightly sand the lumps off. Might go back to soft brush.

 

 

I always rub my shelves with a wet sponge before putting the wash on.  Helps to not grab

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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 ended up just giving a light sanding when finished to get rid of the high spots. Next time I will wet the shelves first.

Thanks for all the advise.

Firing another 2 sinks, let the kiln gods be kind.

On the Bartlett slow cone 6 glaze, looks like 16 hrs to heat up and 150 hr to cool down to 1500. The sinks are in the centre of the kiln  with a waster and alumina both sides of the waster.

 

Edited by ronfire
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On 9/2/2020 at 2:04 AM, ronfire said:

150 hr to cool down to 1500

Too early in the morning.  I read that as 150 hours to cool down.  Was doing a quick calculation as to how many days that would be.  Then my brain kicked me and said, no, read that again.

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Well I opened the kiln at 150, unloaded the first sink it was cracked on the heat up . the next sink was still fairly warm to the touch so I left it in the kiln but did not notice any cracks. A few hours later removed it at 130, warm to the touch ,at a closer inspection I saw again a hairline crack Never had this kind of cracks  before I removed the sitter and put in a Bartlett kiln control with SCR relay.  Out of 6 sinks I had 1 that was good. I used a slow glaze program with a 30 min hold at 2100f.   Would the hold cause an issue that I never did with the sitter. The sitter ran 2.5 hrs on low then 2.5 on med then all to high until finished to cone 6.  Sinks where placed on wasters with alumina under and on top of the wasters.. 

I just realized I changed clear glaze that plainsman sells. Could no longer get the plainsman glaze  I used and now have Plainsman 2926B. I will send plainsman an email and ask them.

 

 

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1 hour ago, ronfire said:

I just realized I changed clear glaze that plainsman sells. Could no longer get the plainsman glaze  I used and now have Plainsman 2926B.

This could very well be it! G2926B was made for M370 which is a low expansion clay. Hairline dunting cracks from glaze fit could well be it but would be more likely to show up on pots with a thinner wall than the sinks. Take something else that is glazed with the G2926B and put it in the coldest part of the freezer overnight then put it in the sink and pour boiling water into it and see if it cracks.  Preferably with a thick glaze layer. Which glaze were you using before? 

Sorry to hear about more sinks cracking, must be super frustrating.

edit: nix what I said above, I just found a Plainsman page where they have 340 glazed with G2926B. Only other variable is the vent, wondering if any holes you drilled in the kiln are the issue.

Edited by Min
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I am wondering if it is the new Plainsman glaze  2926B. I was using the Plainsman G2916F before but the store does not carry it now.

Here is a pic of the firing  schedule I just used.

The wife will spend a whole day under glazing a sink and now is blaming me because we never had so many failures with the kiln sitter. The controller should be kinder on the clay than the sitter.

We will not do anymore sinks on orders. Was planning on one for our own bathroom  renovation  this fall but now not so sure.

 

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3 hours ago, ronfire said:

We will not do anymore sinks on orders. Was planning on one for our own bathroom  renovation  this fall but now not so sure.

I am not convinced the schedule is an issue but do not want to fully reject it.  I do feel strongly about the stress that develops around a hole and would at least try a thickening washer of clay  around the hole during construction. It’s really hard to know if minute cracks are developing during drying. I would suggest trying reinforcing around the hole as early as possible during fabrication. This technique has had great success in clay, steel, just about any material we cut holes in. Might be worth a try.

Edited by Bill Kielb
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I will try to have a thicker area around the hole but then worried about the uneven thickness that can cause breakage.

I still have a little of the old glaze that I can pour over the sink instead of dipping it, also will make the new sinks a little thicker and see if that helps. Just getting very frustrated because the sinks where getting popular and now having issues that I did not have before.

 

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14 minutes ago, ronfire said:

Just getting very frustrated because the sinks where getting popular and now having issues that I did not have before.

I totally understand, similar issues with very large flat clock faces here. Making 1/4” thick washers from rolled clay was the easiest method we found and just attaching it early on was a snap and solved  our issues finally. I could easily cut nice round washers to any size needed.

Edited by Bill Kielb
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Ron I threw large stoneware sinks for years. I still use one in one of our bathrooms. I would throw a 1 inch thick collar under the foot (my sinks always had feet) are are glazed everywhere like any bowl top and bottome except foot.  They are staroger that way. I also had most of them with overflows and this collar/tube on the side had a notch for that to fit as it was below foot area. I used this collar for about 6 sinks then made a new one . I still have a collar  kicking around although I'm done with sinks. Most overflows necked down to a palstic tube and then I madea smalll collar that fits a tube that I silconed to sink bottom at the install point.The overflow and below collar had a palstic tube for the water to flow. I also buildt the tubes out of clay but the polastic tube is a better working deal with less chance of falling off as sink shrinks. I made a few with no overflow as mine at home is as well. I also made sinks for denist offices in a whole sale way. Never had all the troble you are experiencing Mine where stoneware  and the denist ones where porcealin.. Made about 30-40 of the denist ones-still have a stack as well no overflows on those.Make nice planters now I suppose .

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The problem is the bottom of the sink should be flat with the outside edge of the sink. I can trim the bottom to include a ring that matches the foot of the sink. The other way would be to make a  doughnut  to fire the sink on if the centre drain sits proud of the bottom of the sink.

But that brings me back to the sinks used to fire well, did have many break and never the hairline cracks when I used the sitter. I am thinking it is in the newer glaze now that I look back at the time frame was about the same time I went into the wall controller, or could be a new batch of clay issues.. even thought it is the came M340 but a different lot #

Next try will be the old glaze, but not sure if I should stay with the 18hr glaze fire as above.

 

 

 

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11 minutes ago, ronfire said:

Next try will be the old glaze, but not sure if I should stay with the 18hr glaze fire as above.

Changing two things at once is a killer.. 18 hours is a looooong time for glaze fire though. The glaze fit could provide issues. A good fit generally puts the clay in ever so slight compression improving the strength of the fired product. Assuming this shape has unique stresses in it especially through firing, I think that your glaze theory could have merit. You could always write a program to emulate the old sitter manual fire and end up pretty close to the old firing to rule that out. Making sinks over and over is a pain though!

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Where is the crack in relation to the underglaze decorations? 

I wonder if the more refractory underglaze isn't what is causing the stress. 

It is certainly an uneven pressure.

Could be the new glaze is pulling on the underglaze differently.

I still think it is an S crack that can't be an S because of the hole.

I'd like to see them "mid dry".

Sorce

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Ron here is my personal sink (no overflow) the hole has a foot that is on sale plane as foot on bottom . The fired and siliconed on later clay ring is for the conversion to a non overflow sink. Its added later to installation to cover the overflow holes in hardware .One thing I did notice is all manufactures can have different from (in my case brass) flange sizes.I'm talking about the inside the bowl other cut out to flush the drain with bottom . I had a few from various manufactures and always made them brand specific.

 

IMG_3514.jpeg

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9 hours ago, Mark C. said:

used brands like Moen and Kolher etc.

Back then the amazon was jungle not a web site

Have seen plenty of folks use the retrofit pop up assembly drains from the big box stores. They just measure the escutcheon and throw their piece x% bigger with some additional room for safety..  Plumbers  putty,  hand tighten In place and ya got a nice finished drain with a Drop rod pop up in it. Seems to make  a good impression on most contemplating purchase actually. I think about $8.00 at HD made by Everbuilt I think. Whoever that is?

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