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Can Thermal-Shock Be Undone? The Results Of My Inadvertent Firing.


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My house and studio burned down in Calif.'s Valley Fire (which should have been named the Cobb Fire as it started right down below our house). I had pottery everywhere in my house and outdoors, too, and everything was lost.  There are 8 pieces that look pretty good, but the color is not as vibrant, and the 6 that are ^6, when tapped with a fork, have that dull thunk of a sound that I associate with thermal-shock or some action that compromises the structure of the pot. About a dozen more pots, mostly mugs in my studio where I had about 100 of them ready for art fairs, are all in one piece, but look very ashy and when lifted, can be broken it into pieces with my hands. Obviously not functional. 

 

I have numerous samples of five different kinds of clay and each responded differently to the fire.  Oldest are my ^10 reduction which were most of my personal pottery. Of those, the large (for me) vases, lamps and bowls were made out of 8-11 red, which I threw with in the 70's, and as a group fared best. Two of the largest ones actually are not only intact but ring true. It's just the glaze that lost that wonderful richness of a reduction firing. The glaze is flat and/or extremely dry like underfired pieces.  Also in ^10 reduction I used Danish white and the few that are intact are covered in globs of ash, etc. but many ring true, but again the glaze is dry and flat. A few pieces were in porcelain (Coleman) but they looked no different than the Danish white.

 

I also had many pieces of ^06, mostly handbuilt pieces made as samples from 25 years of teaching students pottery. This as a category fared better than my ^6, although all are covered in ash /globs and none are keepable. Some were in Navajo Wheel, a ^06-^6 red clay which I use a lot, and the rest were Low-fire White, which were the ones that did the best.

 

All my new (6/2014 to 8/2015) work is ^6, Navajo Wheel and B-Mix ^5, and I had at least 400 pots ready for my fall and Christmas Fairs. Five pieces are intact, but all sound 'thunk', but the glaze, although a little drier than it should be, looks the closest to how it's supposed to. Three of them are small bowls and I'm afraid to test their strength by trying to pull them apart, because I fear they'll break and I won't have any intact pots to remember. The other two are little vases. The vast majority of the pots are in pieces, but few maintain the brightness of their before fire life. I have salvaged ~15 Costco plastic storage containers of broken pots and shards. I plan to make a mosaic wall (or 2 or 3) from them, but they mostly look like they've been through a fire. That's fine for some of the mosaic, but my design needs some brightness, too. 

 

My questions are: What would happen if I refired the intact pieces that don't ring true?  I'm assuming that the reason is thermal-shock from the fire, too hot too fast. Would it/could it undo the thermal-shock or would it in all probability do more damage? I taught the daughter of one of my neighbors and they ordered a teapot and 4 cups for her college graduation. Their house also burned but the teapot and 2 cups came out intact, but thermal-shocked. She wants to know if I can refire it. Would that work? To what cone would I fire? What about just refiring shards to brighten them up so they don't look so ashy? At what cone does ash melt?  I really need the help and advice of the experts in this forum.

 

 

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The pots are cracked and refiring will only make it worse.  I know this for doing it -not theoretical. I dug some pots from a nieghbors house that burned down and they are as you said .. Just make new ones and move forward. The thing about the house fires is they dull the glazes as you have seen-refiring can flux them but the more you fire them the weaker they become. Test one if you like-its needs to go to the same cone the glaze was fired to and it can run more as they usually do..as with any refire pot.

Mark

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I don't have any experience, with refiring a pot, that went through such a process.

 

The closest that I have had, is refiring Raku pieces.  In the case of those, as Mark stated, the refiring made them worse.  Unnoticeable, potential cracks, became very noticeable, very obvious cracks with a refire.  

 

I would just keep them as they are.  They are survivors of a terrible ordeal, and while they may not look like the way they were intended/ once did, that ordeal makes them special.

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Thank you for the advise/information. Not what I hoped to hear, but down deep I knew that nothing would make the pots right again. What about refiring just some shards, particularly the ^6 ones with the bright underglaze colors? I was thinking about refiring them to my bisque temperature, ^07, specifically to melt the ash which I'm hoping will brighten the colors.  A friend of a friend is giving me an old Cress electric kiln which I'll use for bisquing. We're putting in 220 next week, and I reordered a wheel which we'll pick up tomorrow, so I hope I can make some time to throw so I can fill the kiln. Putting my life back together is a huge process.  I lost all my pottery resource books that used all the time, so I'm now really relying on the expertise that this forum represents.

 

Also, all my refractory kiln shelves are also brittle which is a big surprise to me. When I lifted one it snapped in two. I would have thought that they would have survived. The 5/8" ones were in the garage with my electric kilns and the 1" ones were out with my ^10 kiln.  All were stored upright.

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The thing about house fires is uneven heating which is bad for most ceramic materials including shelves-pots-glazes.

If the fire dept sprayed any water that to is shock on stuff.

Since you said it happed so fast and at the at start of that huge fire I assume its not a water issue just wind and flame which is uneven heating. I'm curios if the shelves (non electric) where mulite or silicon carbide or the hollow ones?

Mark

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what a horrible experience!  i just read about the terrible fire that ruined so much of your area.  someone here will know how to get in touch with the clay community's disaster fund.  i cannot remember the name, i think it is CERF.  if you ask us for replacement books, maybe someone will have something you need.  there are a number of books on my shelves and if you need something specific,  just ask.

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Mark, My shelves were not silicon carbide not hollow, so they must be mulite. My ^10 ones are 1" and I bought them straight from Thorley's in So Calif back in 1975. The ^6 kiln shelves are the same material bur 5/8" thick. The ^10 kiln maybe would have made it if the large welded sheet metal vent over it hadn't crashed down on it in the fire. 

 

Old Lady and/or anyone else who has books they'd be willing to donate:  Here's a list of the books that I used the most for resource and inspiration/ideas:

*Daniel Rhodes', "Clay and Glazes for the Potter", 

                           "Stoneware and Porcelain: The Art of High-fired Pottery"

*Glen Nelson, "Ceramics: a Potters' Handbook

*The 500 Series: Bowls, Tiles, Teapots, Pitchers, Cups, Plates and Chargers

 

Those were the ones I used most, but any pottery book would be appreciated!

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i will send rhodes, stoneware and porcelain.  apparently the eighth printing in 1974 of the original 1959 book.

 

which edition of nelson do you want?   i have several.  the first, 4th and 5th editions.

 

we will need an address to mail to.

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  • 4 weeks later...

the wettlaufer book has lots of pictures to make you smile but some solid info.  the glaze recipes on page 127 are very useful, simple non-toxic ingredients and able to layer on each other if you like.  the one i call wett. 18 is a very dry matte that takes color from mason stains very well.  i have gotten purple, green, yellow and orange.  have not yet tried other colors and plan to today since i have a firing about to be loaded.  hope the nelson was the one you wanted.

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