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How to Dry a Platter Without Cracks

5/25/2010

13 Comments

 
Picture
Here's what works and what doesn't, after months of trial and error. I'm talking about wheel-thrown serving platters, between 16 and 20 inches across when freshly thrown. Until this year, I rarely threw platters this large. They cracked while drying on a regular basis, I'd say 1 out of every 4 developed a crack in the middle of the floor. I considered the cracks to be random occurrences, because I had not bothered to analyze the problem. This year, as part of my wholesale orders, I needed to produce roughly a dozen big platters. When two of the early ones cracked, I started looking for answers. And here's what I figured out.
   First and foremost, a  large platter requires good throwing and trimming. It must be evenly thick throughout, and well-compressed as it is thrown. A thin area will crack, and a thick area will crack, because these cause uneven drying and shrinking, which the clay cannot tolerate. This factor requires experience and good technique, which every potter possesses in different amounts. But here are four factors that everyone can control right now:

1. Dry the platter on a melamine board. Melamine has a non-absorbent hard plastic surface, with a slightly grainy texture, that does not bond with leather-hard clay, therefore the platter is free to shrink as it dries. The other choices in my studio are wood and drywall, which are useful for other pots but not for large platters. A wood board warps when it becomes damp. A drywall board doesn't warp, but its paper surface becomes spongy when wet. The platters I dried on drywall cracked 100% of the time. That's right, I said 100%. My (unsubstantiated) explanation is that the platters were stuck to the spongy paper surface, they couldn't shrink and therefore the floors split open.

2. Dry the platter on its rim. All pots dry from top to bottom, and a rim dries much faster than a floor because its surfaces are more exposed. So drying a platter upside-down evens out the drying process. When dried right-side-up, the rim will harden and shrink much faster than the floor. When the floor tries to shrink later, the hardened rim does not allow it, and the floor splits open.

3. When the platter is upside-down, support the floor. Before I flip a platter over for trimming, I stack a combination of studio sponges, upholstery foam, and 1/4 inch thick scrubber pads, in the middle of the platter flush with the height of the rim. So when the platter is upside-down, the floor is supported from underneath. Without the support, sometimes the floor of the platter would sink downward while trimming, and these platters were guaranteed to crack later. My (unsubstantiated) explanation is that the flexing caused micro-cracks in the leather-hard clay, which grew into visible cracks later. I leave the supports under the platter for its first few days of drying. As soon as the platter is stiff enough to be picked up, I remove the supports so there is nothing to prevent the platter from shrinking.

4. Cover the drying platter with fabric. My basement studio is very drafty, and uneven drying is a constant battle. But a sheet of fabric is all it takes to slow down and even out the drying process for a platter. Any lightweight fabric works, like an old t-shirt or bedsheet. A sheet of plastic also works, but it slows down the process too much. Using fabric, the platter is ready to fire in 8-9 days. Using plastic, the platter takes 3-4 weeks to dry, unacceptable for a wholesale schedule.

All of these techniques can be summed up thusly: even out the drying process, allow the pot to shrink, and don't allow the pot to flex. I am happy to report that after incorporating all four of these factors in my platter-making process, I have not lost a single platter!

13 Comments
kim hines link
6/1/2010 12:41:01 am

oh thank you for this! i've been having a similar problem w/ my bigger plates as well as platters. i'll have to give these things a try next time i make them. :)

Reply
martha Peddicord
8/20/2010 01:54:25 pm

Hi, Mea, read this with interest, I too have crackidocious platters. Just got hydro cal bats, did you try plaster in your research on how to stop the cracking?

Reply
doug nicholson
5/22/2014 11:47:41 pm

I've purchased the hydro bats and I love them, but I have learned the drying time and evenness of the bottoms are the factors that happen in spite of the wonderfulness of the hydro bats as I get carried away with creating....

Reply
Mea Rhee link
8/21/2010 02:15:32 am

Martha, that's an excellent question. I have been using Hydrobats for several years, which means they do not prevent cracks from occurring. However, they provide a valuable convenience factor, after throwing a platter I can allow it to dry uncovered, and it will be ready to trim the next day, and the Hydrobat helps to keep the moisture content balanced. But once the platter is off the Hydrobat, it no longer has any impact on the "crackidocious-ness" (love your vocabulary!). In my classroom, we use plastic or wood bats to throw platters, and these can be just as successful. But the platters must be covered in plastic sheets and allowed to slowly dry to leather-hard, or else the platter will dry unevenly and promote cracks. It takes about a week to reach leather-hard this way. So it is less convenient time-wise, but if all of my other procedures are followed, it is just as successful.

Reply
Kathy
12/4/2010 09:16:57 pm

Thanks for the advice. But wont the rim get ruined if you put it upside down right off the wheel??

Reply
Mea Rhee link
12/4/2010 10:31:22 pm

Kathy, I guess I could have made it clearer, I don't flip the platter over until it is ready to trim, i.e. leather hard. Until then I leave it right-side up on its bat. Thanks for the question!

Reply
Leonard Baca
2/25/2012 08:42:31 am

Good information, what about temperature? I have my studio in the garage, it gets cold I heat it when I work. So in general the temperature is not even.

Reply
Mea Rhee
2/26/2012 07:28:20 am

Temperature in my studio is not constant either, warm and humid in the summer, cold and very dry in the winter. Sometimes I heat the studio in the winter too, which makes the air super dry. But I find that the fabric cover keeps the platters drying evenly no matter the season.

Reply
Tim McLaughlin
1/18/2014 02:07:33 am

Thanks for your advice. I am cracking like 50 % of every large platter, so do you wet the fabric and how thick do you like for your bottom ?

Reply
Mea
1/18/2014 05:26:49 am

I don't wet the fabric to begin with, but it does becomes damp from touching the pots. I think the dampness helps to slow down the drying. For a platter that large, the bottoms are about 3/8 inch thick.

Reply
Cheryl Daly link
2/26/2014 05:25:59 am

Thank you - I will try these tips : )

Reply
Stephen Mullins link
3/13/2015 12:07:54 pm

Thank you! I have just started throwing platters around 20 inches in diameter and have been wrestling these hogs to no avail - have usually gotten a crack. I will definitely try these methods. Thank you again.

Reply
jameslehner992 link
6/22/2022 04:54:34 am

Thanks for awesome post. I am beginner to these fragile objects so I need more posts like this :)

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    Mea Rhee (mee-uh ree),
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