[R Fraser]

I need some advice about platter related matters. I recently threw 10 platters that started with 3kg to 4 kg of stoneware (Continetal Clay Buff Stone Ware with Ochre), and 2 havecracked in the middle during drying after trimming the foot rings. I had trimmedthem a little wetter than I typically like but had time constraints as usualand felt they were sufficiently firm for trimming. After trimming I put theplatters on ware boards and covered them with plastic sheeting (formerlykitchen garbage bags). For certain the rims were a bit dryer than the center sothere was some moisture disequilibrium, but no more than any other time in thepast. No matter what I do, it seems I lose about 20 to 30% of these plattersabove 15 inches. I am very compulsive about compressing the base as Ithrow. Does anyone have a secret tosuccess with larger platters? Or should I plan for loss and just be happy it’snot half of them (yet).

[kathi]

In addition to covering the entire platter in plastic as it dries, i place lightweight plastic (the weight of a dry-cleaner bag) around the rim of my platters and large bowls. It is very difficult to keep your rim from drying faster than the base or body of the pot - and obviously you know what happens when it does! The only remedy that I know of is patience and time; the moisture level has to normalize and your pot has to dry evenly to prevent it from cracking.
My condolences on the demise of your platters....

[Natania Hume]

I posted a similar questions a while ago. Since then I've been wrapping the rims with a bit of plastic, throwing them on hydro bats, and drying them upside down under fabric. These were all tips I got here. My platters aren't quite as big, but my problem seems to have resolved itself with these precautions....good luck!

[Mark C.]

I throw platters 13-18 inches with porcelain every year. Porcelain dries fast.I rarely see cracking. It can be many factors-.
there are many ways to do this and whatever works for you is best-here what I do

I really compress them then strike them off with a larger thickness wire so they do not grab back on to the bat
I make sure they slow even dry and flip them over as soon as I can which is when the middle is dry enough. I never let the lip dry out.
After trimming I dry them right side up-again slowly at first.
Make sure that they are not to thin or thick anywhere but even thickness.
You can experiment with another clay body if this is a continuing issue.
The more open bodies may work better for you.
Mark

one thing you did not mention was where the cracks are and which way do they run?with the the round or across it?

[Benzine]

I had issues with the bottom cracking, in some of my larger pieces in the past. It was almost always the dreaded "S Crack". So, I just wasn't making the bottom a consistent thickness, as Mark mentioned. I haven't had the issue in years, simply because I've gotten better.

[GEP]

Natania Hume, on 04 February 2013 - 08:46 PM, said:

I posted a similar questions a while ago. Since then I've been wrapping the rims with a bit of plastic, throwing them on hydro bats, and drying them upside down under fabric. These were all tips I got here. My platters aren't quite as big, but my problem seems to have resolved itself with these precautions....good luck!

Here is a link to the thread that Natania is referring to:

http://ceramicartsda...cking-platters/

Natania, glad to hear your platters are working out!

Mea

[Brian Reed]

The only time I had issies with large patters cracking in the middle was when I did not trim them enough. Thick bottoms and thin rims will cause cracking for sure.

[Marcia Selsor]

You didn't mention if you had any support under the softer than usual bottoms. I use soft sponges for support if needed. Others have mentioned foam in the past.
If the bottom sagged while trimming, that can cause the crack.
Other have mentioned good practiced. Even thickness is the key and even drying. You can try waxing the rims to slow down the drying on them.

Marcia

[brian sarama]

During Graduate School I was making 28 inch porcelain platters. I would leave 2 inches or so from the bottom dip of the platter to head of the bat. I would throw them, wheel trim a decent amount, and cut it off. I would normally throw early in the evening and would leave the platter totally uncovered until the following morning. Once the rim stiffened up enough I would then cover the rim lightly with really thin drop cloths (can be purchased at any Home Depot or Lowes) and lay news paper in the middle. Throughout the day I would change the paper out until it was strong enough to flip over , this would normally take a day or two. Once it was able to flip it over I would remove the bat, scrape the remaining clay off of it and the lay more newspaper on the bottom, and once again flip it back over. After repeating the method a few times I was able to trim my foot ring. After decoration was complete I would let them slow dry under plastic, on top of news paper, on of a sheet rock board. Ive never had a platter break in the green state. My major issue was during bisque. I would have a kiln load of platters in a large gas kiln, only to have the majority dunt during cooling. I have since fixed this issue with a combination of stilting the platters up on wads on top of a stretcher slab, packing bricks around the rims (to help hold heat and ensure an even cooling process) and once firing the wares.

I hope this helps.

[R Fraser]

I should have added that I use a large cut off bow I made to free the platter immediately after throwing. The cracks pretty much cut down the middle, more or less tracing the diameter of the platter. With previous platters I had used 2 inch high density foam bats to support the span of the platter. This time however I threw a large clay chuck to trim the platter and the middle was un-supported. Several - probably all of them that cracked - 6 now, were soft enough I am sure there was some sag, and the dryer ones probably developed the cracks while trimming since the chuck really only supported the outter edge of the flat part of the platter.

As an aside I should have searched the forums first before posting. Thanks to the moderators and regulars for not posting the "have you tried the search feature before posting" reply. The links posted as well as the replys were very helpful. I have just thrown 2 more to replace the first losses and I will try to keep the rims from drying too fast. Does using wax resist ever prevent the rims from fully drying and increase the risk of cracks during bisque firing?

[neilestrick]

Even with wax the rims will dry out enough for bisque, it may just take a day or two longer. In my experience, thickness seems to matter more than anything on large platters. If it's thin and even, it will survive. I make 20 inch porcelain platters and don't really treat them any differently than small sandwich plates. I do trim them on a chuck, to take the weight off the rim, but I don't slow down the drying or anything like that. You just have to be very careful to trim them thin.

[Marcia Selsor]

The wax just slows the edges from drying too fast. Kurt Weiser taught me this. He used this technique on very large slab convex forms decades ago.
I wax the edges of my large flat slabs. It helps prevent warping as well from uneven drying. The crack straight across the middle sounds like a drying problem maybe due to unevenness. Slow down the drying and get everything even.

Marcia

[R Fraser]

Thanks to all that replied to my post. I found the suggestions most helpful. I found the round foam pads I purchased a couple of years ago specifically for the purpose of trimming large platters and started to use them again as well as using a thin plastic recycling bag with the center cut out to the size of one of my 12inch bats to keep the rims from drying. I threw another 8 platters from 9 to 10 pounds resulting in around a 16 inch platter and not one has cracked.

I really think that in addition to keeping the drying even, trimming the foot ring with the center of the platter well supported is critical. I am certain the last group of platters were lost because I was trimming them on a thrown clay chuck that did not offer any support to the center, and the rim dried too quickly. At least I got a good look at the middle of the platter to verify that the base and rim was even in thickness

[autour de la terre]

R Fraser, on 04 February 2013 - 02:18 PM, said:

I need some advice about platter related matters. I recently threw 10 platters that started with 3kg to 4 kg of stoneware (Continetal Clay Buff Stone Ware with Ochre), and 2 havecracked in the middle during drying after trimming the foot rings. I had trimmedthem a little wetter than I typically like but had time constraints as usualand felt they were sufficiently firm for trimming. After trimming I put theplatters on ware boards and covered them with plastic sheeting (formerlykitchen garbage bags). For certain the rims were a bit dryer than the center sothere was some moisture disequilibrium, but no more than any other time in thepast. No matter what I do, it seems I lose about 20 to 30% of these plattersabove 15 inches. I am very compulsive about compressing the base as Ithrow. Does anyone have a secret tosuccess with larger platters? Or should I plan for loss and just be happy it’snot half of them (yet).

Hi, one important point is NEVER LEAVE WATER STAGNATING WHILE YOU TURN YOUR PLATES OR OTHER OBJECTS ! AND YOU WILL NOT HAVE TO WORRY ABOUT WET CENTERS. Enjoy potting. Judith

[chilpot]

R Fraser, on 04 February 2013 - 02:18 PM, said:

I need some advice about platter related matters. I recently threw 10 platters that started with 3kg to 4 kg of stoneware (Continetal Clay Buff Stone Ware with Ochre), and 2 havecracked in the middle during drying after trimming the foot rings. I had trimmedthem a little wetter than I typically like but had time constraints as usualand felt they were sufficiently firm for trimming. After trimming I put theplatters on ware boards and covered them with plastic sheeting (formerlykitchen garbage bags). For certain the rims were a bit dryer than the center sothere was some moisture disequilibrium, but no more than any other time in thepast. No matter what I do, it seems I lose about 20 to 30% of these plattersabove 15 inches. I am very compulsive about compressing the base as Ithrow. Does anyone have a secret tosuccess with larger platters? Or should I plan for loss and just be happy it’snot half of

This, or some variation of this is something most of us have experienced. Your clay body might be more prone to drying cracks than others, but, Try cutting a round hole in the plastic bag (on the top, in the center)about 4 to 6 inches wide and this should encourage more even drying. If that doesn't work try a different clay body. Geoffrey Borr- "chilpot"- Chilmark pottery