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Marcia Selsor

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Posts posted by Marcia Selsor

  1. I just had a full kiln load of bisque Way over fire. It was suppose to fire to 06 but went to at least cone 8.

    I connected the wires wrong to the thurmo couple & everything came out burnt.


    ** Question. I know for raku, the clay needs to be open & UN vitrafied.

    Will it still be Ok to Raku without cracking?





    If you really did hit ^8 then the clay will be too vitrified to withstand the thermal shock of a raku firing and it will crack.




  2. Higher firings do cause more wear and tear on kilns but that is the price of doing business. The question should be more of what do you want to do.

    Lisa Naples, for example, makes beautiful functional earthenware fires to ^2 or 02, I don't remember. She just said she fired her earthenware to vitrification so it is hard and durable. She learned that from a ceramic engineer who took her class.. I met Lisa at the show after NCECA. She really does lovely work. I would say that most earthenware fired to ^06 is not vitrified , will collect moisture, will be punky, and may have steam escape if used in a microwave which might explode. Majolica fired onto earthenware is usually bisqued to ^04 as you are doing, or higher ^02 sometimes. It is also glazed all over stilts in firing to avoid moisture absorption which can cause the glaze to flake off. That is why you often find the three marks from stilts on the bottom of majolica. So you really need to decide what you want to do. But some of your reasoning seems a little misinformed.

    Check out Lisa's work. She is an inspiration for earthernware.

  3. I have bought a paint spray to use as a glaze spray but can't afford a spray booth with extraction. Apart from using it outside on a still day, in a large box perhaps lined with newspaper, and obviously wearing all of the necessary protection (esp filtration mask) does anyone have any hints about extracting the fine spray that doesn't reach the piece to be glazed?



    There are lots of good suggestions. When I was in school ages ago, one suggestion was find a used dryer with the heating elements burnt out and still has the exhaust in tact. Gut what you can, cut off the front and the fan/vent should be in the back. Clean up sharp edges. The blower should run on 120V.

  4. Thanks Jessica!

    That does help a lot :) I am still wondering though, why people use them? Everyone I know in Europe has never used them ! Any insight on that? I know they show you heat distribution etc ..but unless your kiln is on the fritz and inconsistent what is the need for them? Is it because people mostly use manual as opposed to digital here??huh.gif



    I was just about to send you the same site for the cone chart that Jessica sent. Temperature cones have been around since the Northern Song Dynasty. Wedgewood made his own. Orton made them beginning 1896. <- from Wikipedia. More people have gone digital in the last decade or so. For wood or soda firing, digital pyrometers could be damaged. Maybe old habits die hard. According to ethnoarcheologists, pottery communities and fishing communities hold on to their traditions more than any other. You are of a younger generation who grew up with digital pyrometers. It is the norm for you. It is recommended by many to use 'witness' cones in the kiln with the digital controls. It may just be old-fashion.

  5. Marcia (+ all),


    For calculating input for my kiln design work, for hard refractrories I use 15,000 BTU /hr. /c.f., for (standard) insulating reftractories I use 10,000 BTU/ hr. / c.f., and for RCF (fiber) refractories 7,000 BTU / hr. / c.f.. Obviously, blending those types of materials in any significant way results in intermediary values.


    The piping requirements between the gas storage and the kiln are, of course, another whole little technical consideration, as is mentioned above by mudlark. This is true no matter what volume the gas storage is.






    Thanks for the fiber and more accurate brick figures. My info was from the ancient Soldner Kiln book I believe. And yes...piping is a whole 'nother ball park.




  6. Hi Im very new to pottery and watch this forum closely for tips and techniques. I look constantly on the internet for pottery information. I took a beginners class in march and now have joined a pottery group. Ive been learning thru watching other potters..asking tons of questions and trial and error. I was wondering if you could give a beginner one piece of advice what would it be? Also, is there other pottery sites you visit? (nothing wrong with this one...just like to look around)




    To broaden your awareness of history, go to museums, study form. Go to contemporary galleries and see what is being done. Go to the library and look at magazines and books. Reading is greatly underrated. Draw, keep notes of what glazes, slips etc. you are using, how it is fired. As for archival paper, I have sketch books and glaze notebooks going back 45 years. Some are yellow. The purple dittos are really faded but still legible. Many pages have glaze or wax on them. I have four large glaze notebooks and two recipe boxes. Lots of sketch books from travels and for the studio. Find forms that interest you, draw them, alter, dissect, and go 3-D with them. Figure out the solutions to forming challenges.

  7. Not sure why your re-glazing is not having the desired effect. I just put on more glaze without re-heating. I mix my own glazes. Maybe there is more clay content in them that makes them stick to the glazed surface. Try adding a little corn syrup to the glaze you are using to reglaze. Let that reglaze be thick. Try to get a visibly thicker coating on the reglazed area. To get the glaze thicker , let it dry out a little.leave it uncovered for a few days...depending on the humidity where you live.



    I've had very good results using a hot plate to heat the peice to be re-glazed with cone 6 glazes. Heat the piece to about 250 FH then re dip or spray. The only difficulty is cleaning the bottom after dipping again.


    Are you re-waxing the bottoms? That would make it easier if you are dipping.

  8. I'm in my Confused Early Stages, so please bear with me.



    Should I choose a STONEWARE clay body such as Minnesota Clay MB STONEWARE

    or a lower-fire EARTHENWARE?





    I'm new to this and want to keep things as simple as possible.



    Tiles and larger flat forms involving relief sculpture - to be affixed to interiors of buildings as typical cermamic tile is. A kitchen backsplash, a fireplace surround, a segmented mural.



    I intend to use paper clay methods as much as possible.



    I hope to build a natural gas kiln. I want to limit energy costs and kiln construction costs as much as possible. Am I correct in thinking earthenware clays and related glazes fire at much lower temperatures than do stoneware clays. Will choosing an earthenware instead significantly reduce my firing costs and kiln construction costs? Any advice appreciated.



    Finished product must withstand the knocks and scapes and washings that occur in any household. Imagine the abuse a doorframe suffers. In many instances, I will not employ a glaze. My work does not need to hold water (as vitirified clay can) but it will likely be washed with water and mild cleaning products occasionally - especially if a kitchen surface. Would an earthenware body stand up to houshold impact and washings, or must I opt for stoneware fired to vitrification?



    I want as white a clay body as possible. The MB Stoneware (per link above) fires nearly white in oxidation. Is there an earthenware that will meet the "abuse standard" described above and also fire nearly white in oxidation?



    If my question is too broad, can someone please point me in the direction of an online source whereby I can educate myself further.








    That is way more than one question. You need to figure out a lot.

    1. why build a natural gas kiln if you are going to do low fire oxidation?

    2. Gas flames tend to warp flat tiles. Oxidation is more gentle for not warping because of the radiant heat.

    3. You should fire your clay to vitrify if you want it to withstand bumps and household abuse. Otherwise it will be soft and weak.

    4. earthenware fired to vitrification is hard and durable.

    Here is some recommended reading from my Architectural ceramics workshop handouts:

    Recommended Reading On Architectural ceramics:


    Thames and Hudson Manual of Architectural Ceramics by David Hamilton


    Architectural Ceramics by Peter King


    Architectural Ceramics; Eight Concepts


    Large Scale Ceramics by Jim Robinson


    Handmade Tiles by Frank Giorgini


    Terra Cotta Skyline by Susan Tunick


    PARIS and the Legacy of French Decorative Ceramics by Susan Tunick


    American Decorative Tiles by Susan Tunick


    On Technical details:


    Setting Tiles by Michael Byrne


    Working with paper Clay and other Additives by Anne Lightwood


    Shape and Surface by Lana Wilson


    Ceramic Glazes by Cullen Parmelee


    Elements of Ceramics by F.W. Norton


    The Extruder Book by Darryl Baird


    Other Resources


    Friends of Terra Cotta


    Tile Heritage







  9. I have mixed a batch of Randy's Red - Cone 5 Glaze. I am getting more of a muddy brown than reddish brown. If anyone has used this common recipe - do you have any thoughts on how to adjust recipe to get the "red' back.



    I mix glazes for a local art center and just recently discovered that if you use Special red iron oxide (much redder and much more expensive) the Randy's will be red, sometimes tomato red with blacks and blues. For years we only got browns until I changed the RIO. No need to worry about holding, etc. as we fire 3 different kilns, all to cone 6. Results vary by kiln but all come out red.



    What kind of RIO are you using that is so much redder than RIO that isn't so red? Crocus Martis is purplish. Spanish red iron oxide is fine red. Could you specify what it is you are using? I have three RIOs in my studio, plus Black Iron Oxide.

    Inquiring minds want to know.


  10. Hi.


    The vaporization rate of propane from the liquid state (volume storage form) to the gaseous state (what you actually burn in most potter type burners) is mainly dependant on a couple of important factors.


    The first is the outside air temerature in which the metal storage tank is located. Generally speaking, the higher the ambient air temperature, the larger the volume of propane that can be vaporized per hour from a given tank. So a given sized tank will be able to vaporize less gas on a cold day than on a hot day. One in the sun will work better than one in the shade. One exposed to a really cold wind will not work as well as one burried in the ground (as long as the ground is warmer than the wind temperature). And so on. You usually design a system around the lowest ambient air temperature in which you need to fire.


    The second factor is what is called the "wetted area" of the tank itself. This is dependent on the exact geometry of the tank and the orientation of that tank*. It is the interior surface area of the metal walls in square inches/feet that is actually in contact with the liquid propane. The more contact area, the more heat energy can be absorbed from the ambient air into the store of gas. The standard tanks have a pretty well known factor for this for any given gas liquid volume (standardized).


    It all actually gets a bit more subtle... with factors such as whether it is still ambient air or air with a wind, the relative humidity of that ambient air, and so on. For example whern the tank gets condensation or (worse) frosty on the outside due to high huumidity and a cold mass of gas, the heat transfer from the air to the gas decreases.


    What is really driving all this is the latent heat energy in the liquid gas store that drives the evaporation of the gas off the surface of the tank. As the temperature of the liquid propane goes down, just like hot water versus cold water...... you get less evaporation in a unit of time off a given surface area.


    A 9 cubic foot kiln is not going to draw all that much in the way of BTUs per hour. A fiber kiln, due to the lack of thermal mass of the kiln itself, makes that peak draw even less. You are likely looking at a peak draw of about 60,000 BTU/ hr. or so. And remember that is not a continuous withdrawal rate. You only reach this rate toward the end of the firing. The overall average is lower. But you typically use this for a "safety factor" for a well less than full tank. (Standard design principles utilize a 1/2 full tank in doing the calculations.)


    Given that basic info above, and assuming you are using ASME type tanks, you likely need a storage of about 115 to 150 gallons. The former should cover temperatures down to a little above freezing, and the second should cover you down into the just below freezing ambient air range. If you live in a place that it gets to -20F ..... and you still want to fire.... the storage volume needed goes up fast wink.gif







    * Do not tip tanks on their side to an extent that there is a danger of withdrawing liquid propane into a system that is designed for the vaporous gas form. BAD thing. Liquid withdrawal burners exist.......... but they are not typically used by potters; provence of industry.


    PS: The above is based upon "code". If you are dealing with governmental type people in all this or insurance companies... this is the kind of thing thay will expect. You'll find that potters often go to gfreat controtions to make too small storage tanks work.... such as spraying with warm water, sitting small tanks in warm water baths, and so on.


    John's points are all excellent. I use 4-30 gallon tanks plumbed in pairs to fire my 15 cu. ft. raku kiln. It is 2" fiber and I can fire several different sessions of 5-8 batches without refilling. You would probably need more gas because you'd have a longer firing. However, for small vertical tanks, your evaporation surface stays fairly constant as the gas is depleted. If the burners use the gas faster than it is evaporating from that surface, you get ice buildup. That is why it is good to pull vapors from two tanks simultaneously for one burner. My tanks don't freeze. I had three tanks for 2 burners in Montana. Here in steamy south Texas, I have four tanks for 2 burners with 2 tanks on each burner. I have a regulator set for 3-5 pounds pressure at maximum. Follow your BTU estimated need, use the right size orifice for LPG to obtain that BTU output needed at max. temp.

    There are charts. Your gas company should have them. An old extimate for hard brick was 120,000 btu's/cu. ft. Insulated brick was 30,000 btu's/ cu. ft.

    I would have to research what fiber requirements are. Do your homework and it should be fine.



  11. What happens to cobalt oxide if I put on a clear glaze and fire to earthenware 1060. Also what is nikel oxide used for?


    1060 F is really low. Do you mean 1060 C? If you have a glaze that fluxes at that temperature, you could use the cobalt and nickel as a wash mixed in with the glaze. Cobalt could blister if used in high concentrations...same for the nickel. You just need 1-2% for the desired color effect.



    1060 C is Cone 04 (more or less)


    and 1060 F is below ^022

  12. So then the learning curve is proportional to the amount of reclaim and wasters in the mosaic pile. That means I must be learning a lot! Another learning curve occurs due to modularity. I became aware of this at the first Orton Cone Box Show I attended at Baker University in Baldwin City, Kansas. A better way to explore many surfaces is create many works with a fast-turn around time. We like to say "repetition" but actually you learn more from 300 different works with appropriate surfaces developed for each work. So instead of 100 teabowls, all the same, 100 teabowls all different, with 100 surfaces, all different. Remember that in Kyoto Technical they have to do 10,000 tests!!!


    There were moments when my reclaim clay & mosaic tile piles went down to little if nothing, but mostly it had to do with using the same clays and making the same forms repeatedly. I guess it is a confidence booster, but not always sure what is learned.


    Anyway, for beginners, I recommend small works, small kilns.


    h a n s e n




    [.quote name=Marcia Selsor' date='07 July 2010 - 06:59 AM' timestamp='1278503955' post='1384]

    I am not sure that suck factor should decline over time. The truth is, if I make too many good pots in a row, I realize I'm staying in a safe zone, not pushing myself or taking chances. I loved Simon's realization that his suck factor peaked when he was in grad school, trying a bunch of new ideas and considering other people's criteria. I try to keep that going beyond grad school, seeking out crits, pushing myself into areas where I am weak or uncomfortable, and generally challenging myself to push everything just an inch past what i am comfortable with.



    Good point. I have been experimenting and doing some non-clallenging pots. I have a climbing SF index. I decided to stop. Begin fresh and move into a new direction. In this slow economy, I have the time to experiment and no need to rush. Challenge is the key and as you say, Kelly, that is where the SF should be healthy. Go outside the comfort zone.






    I think the bar of eligibility rises on the suck factor, the more critical we become of our own work. That is good. I try to minimize the really sucky pieces, but then I find it boring not to be challenged and trying new things. So a healthy suck factor could indicate a higher learning curve.

  13. Hi All, I want to buy a slabroller, what are others experience of studio-based slabrollers. I am setting up a studio following my foundation art degree and want to make lots of slab-built items, (many tiles/vessels etc). I have used the college slabroller and am impressed with the ease/thickness/drying of slabrolled clay versus hand-rolled clay, but because of the expense, want to make sure that I buy the right one. I do not want to buy a hobbyist one, as will be using it for business. Would a floor-standing or table-top one be more suitable?? I am also purchasing a second shed to house this and more equipment, (as ceramics are taking over my house), so need to make important descisions on size now!!!!!!!!! Also, where would I find a secondhand one, as a google search only found a very small one on e-bay!! I live in England (Essex) so would have to be east of England-based. Any ideas or thoughts anyone??? Cheers, Gigirouge



    I used a German made slab roller when teaching Architectural ceramics workshops at La Meridiana in Italy. I liked it. I can't remember the brand name. You could contact La Meridiana and ask. My classes really ran a lot of clay through that machine. It is very sturdy.

  14. Thanks for analysis Chris! It's cool to see how the clay is really moving. It's also refreshing to learn facts about clay (there's so much dogma floating around, I wish the culture of pottery would adopt an anti-dogmatic attitude).


    I have something to add about stretching a slab across the grain. It has nothing to do with keeping a tile flat, but I do think it affects the shrinking behavior of clay during a cone 6 glaze firing.


    I make a lot of square plates from slabs that are formed on slump molds. At first, I would open a new bag of clay and cut the amount I needed from the end of the block. Then I would stretch out the clay with the heel of my hand to about 9 inches wide, which is the width of the slab I need. Then I put it through my slab roller in the direction perpendicular to that 9 inch dimension.


    One day, thinking I was being very clever, I realized I could remove the clay entirely from its plastic bag, lay it on its side, and cut off an amount of clay that was already 9 inches across. Then I could skip the step of stretching it out to 9 inches, and put it straight through my slab roller instead.


    The plates appeared square throughout the whole process until I put them into a cone 6 glaze firing, when some of them would emerge as rectangles, because they shrank more in one dimension than the other. It took me a while to put it together with my clay cutting shortcut, but ever since I did I have been making reliably square plates again.


    So stretching the clay in both dimensions does affect shrinkage at cone 6. But what's interesting is that a rudimentary stretching from 6 inches to 9 inches, done with the heel of the hand, provides the same amount of shrinkage regulation as a drastic and precise stretching from 6 inches to about 20 inches done with a slab roller.




    Chris and Mea,

    Both experiments are interesting. I , too have a bailey slab roller. I flip and turn my slabs for each pass through the rollers. I like slab rollers with dual rollers. I worked on a Brent for several years where the adjustable boards were on the bottom. I got uneven thickness for my slabs of 25" or so. The surface discrepancy is really interesting to think about. Thanks for the input.

  15. I'd like to post pics online in the Ceramic Arts Daily forum but one of the requirements is images size, 500 k. How do I get this? My camera normally shoots 1200k pics. It's a Canon Powershot 3.2 mg, my Mac is a PowerBook G4 with iPhoto and Preview software for managing photos.

    - h a n s e n -


    Open your photo in Preview. Under tools menu, go to adjust size. you can reduce it there. I have a MacBook

  16. Thanks Marcia for the quick reply. I was stumped. It sounds like it was the last option. I couldn't put any other pieces in because it filled the bottom shelf and no room for posts to put another shelf and when I tried the reverse, smaller pieces first and posts it made it too high to close the lid. So it was alone w/lots of space above it. But your options raised another question (which shows how much research and further studying on kiln firing I need. I was told I didn't need to put peep plugs in, so I never have. What are the ins and outs of this decision?


    Do you have any workshops in Brownsville. I am in Louisiana and desparately in need of some, but don't know how to choose which ones come first. I have two years study at the local university in ceramics, but am winging it alone now.


    Thanks once again. Cyndi





    When firing you can leave the top peep plug out but plug the rest. When you reach the temperature, plug all peeps to avoid drafts.

    I am working in my own small studio and not doing workshops here. I may be doing some next summer and fall. When confirmed, I will post on Event forum. I had a busy year last year. Quiet this year. Getting lots of ideas worked out.

  17. Hello! I'm just looking for any ideas, tips and helpful insight from people whom have started up a studio in a space that was not exactly studio-ready.


    I was lucky enough to move into a building that had an extra annex for rent. This space had been used as my landlord's office and storage. I was given the opportunity to rent it out, and here I am. Now I find myself looking for the best way to utilize this space. It has two stories, approximately 1000sf, no faucet or water. On the first floor I have hooked up 2 kilns and will be using the rest of the space as inventory and a glaze/assembly room. I plan to use the second floor as my work area (its pretty wide open.) I do sculpture, so no wheel. Just an extruder mounted to one of the walls.


    I've been given permission to tear out the cheap carpet, and ideas for flooring material?


    As for the studio layout, will I just have to feel it out - or should I try to plan where I want everything to go?


    Other advice/tips?







    To keep a small space versatile, I put everything except my slab roller on wheels. Check ebay for casters by the dozens.

  18. For the last year I have been trying to make items for the garden that are larger than the household items of my past. I can't seem to get them fired without cracking and breaking up in the kiln. One item is a pagoda. It is about 17" tall after construction. I make it in parts and then fire it together with glaze. The other item is a stepping stone about 1/2" thick and flat.



    I put some demonstration pics on my American Potters pages. You can see the right angle jig there. There are some corbels shown that were made using that jig. It is a simple construction of plywood and 2 loose boards slipped in to make a cradle to support slabs at a right angle. I think you could use one for your pagoda.

  19. I have mixed a batch of Randy's Red - Cone 5 Glaze. I am getting more of a muddy brown than reddish brown. If anyone has used this common recipe - do you have any thoughts on how to adjust recipe to get the "red' back.



    I agree. Holding the temperature even only for 20 minutes at ^6 and again at 1825 will make a big difference. Also muddy color is when it is a little thick. This is a touchy glaze. A thin but not too thin coat really goes red. One of my kilns has a cone setter. I just push the button back on and hold it at the high temp. for 20 minutes and let it drop. Then turn it back on again at 1825. If I miss it, I just turn it back on and take it up to that temperature and hold. I haven't held it for more than 30 minutes.



    What happens in iron red glazes is that unless "bumped" or re-fired they come out brown. Because the cooling is too fast for iron to form the red coloration on the surface of the pot. Sometimes adding more bone ash in these glazes helps, so i am told. Does this help? The way it was first told to me is to cool it to very dull red then bump it back to cherry red, but nowadays we don't look into the kilns which is a unsafe practice, do we?




    I am using a slightly different ^6 oxidation red from Michael Bailey's book.

    I don't refire to ^05., I just hold the kiln at ^6 then again at 1825. If I miss that temperature as it is dropping, I turn the kiln back on, say..at 1700, and take it back up to 1825 and hold for 20-30 minutes. I am getting nice reds. But, if the glaze is on just a little thick, it will go brown.

  20. I am not sure that suck factor should decline over time. The truth is, if I make too many good pots in a row, I realize I'm staying in a safe zone, not pushing myself or taking chances. I loved Simon's realization that his suck factor peaked when he was in grad school, trying a bunch of new ideas and considering other people's criteria. I try to keep that going beyond grad school, seeking out crits, pushing myself into areas where I am weak or uncomfortable, and generally challenging myself to push everything just an inch past what i am comfortable with.



    Good point. I have been experimenting and doing some non-clallenging pots. I have a climbing SF index. I decided to stop. Begin fresh and move into a new direction. In this slow economy, I have the time to experiment and no need to rush. Challenge is the key and as you say, Kelly, that is where the SF should be healthy. Go outside the comfort zone.

  21. No, paper clay is alive and well.

    Google Graham Hay ... He might have some forum links on his site or be able to recommend one.

    Many of us regularly use paer clay for a wide variety of uses and can answer questions.

    I have a paper clay section on my site www.ccpottery.com


    Thanks, Chris. I visited your site. Your murrinis patterns are so sharp and your colors sing. Really beautiful.


    I read your paper clay section while there. Despite reading Rosette Gault's book and your own very helpful presentation, I still don't understand an extremely basic P'clay concept: That is, can I mix my celluose fiber with typical damp/plastic stoneware clay, or must I mix cellulose fibers with dry clay body (powder)? I read the whole book and still don't get it (duh).


    I intend to try Minnesota Clay MB STONEWARE at first...unless you or anyone else warns against it.




    I think not. I can't see how you could mix cellulose evenly into damp clay. I mix cellulose with dry batches in my Soldner mixer. You could try making slip from scrap clay and add cellulose to that then dry to a workable consistency...I use plaster slabs for drying paperclay made in this process.

  22. Hi All, I am fairly new at clay; experientially but loving it all my life. I started experimenting in paper clay recently and being eager to try on my own I have been mixing w/an auger and sometimes by hand my own paper clay. I use whatever clay I have already; ie cinca blanco, cinca roja or B-mix, all Cone 5 clays. I have read and now am rereading Rosette Gault's PAPER CLAY. I do mostly handbuilding. I succeeeded w/a bird bath in two parts totalling 27". It came out beautiful. It was mixed w/the auger and low fired all the way. Then I made meditation sculpture and the base was a lilly pond. It was handmixed, B-mix clay w/cheap toilet paper, low fire bisqued after drying for two weeks. It made it great thru the bisque firing and held 5 quarts of water w/no leaks or cracks. I was sooooo excited. THEN I glazed it w/Coyote Clay Cone 5 glazes and fired it at Cone 5 alone for nothing else would fit. When I took it out I was devastated. It had split vertically on one shoulder and horizontally on the other and straight down the front center between the hands. The glaze job was beautiful and it held about an inch of water but that was it. I can't figure out why it survived the bisque firing but not the glaze firing. Any help would be greatly appreciated becuz I love working w/paper clay. Thanks, Cyndi


    P.S. I have a Paragon Electric 27" kiln.


    Could it have cooled too fast? Large pieces can easily dunt on cooling which eems to be the case as per your description of the straight cracks. You could try insulating your kiln with a fiber blanket on the lid, program to down fire, keep the peep plugs in the peeps, fire with a lid inside the kiln towards the top, or fire with a more densely packed load. If you fired this piece alone, the kiln may have cooled off too quickly.






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