Guest JBaymore Posted July 29, 2012 Report Share Posted July 29, 2012 no matter what you do in a kiln, heat energy will not move from areas of lower concentration to areas of higher concentration (a basic concept from the Laws of Thermodynamics). For those of us who sometimes have trouble with the law, you're not talking about a higher concentration of mass (pots, shelves, etc.) but a higher concentration of heat or, in other words, hotter area of the kiln, right? Jim Jim, Think of it like water flowing downhill. Water does not flow uphill unassited.... you need a pump for that. (A heat pump is used for making heat energy go "uphill" . ) Does that help? Potter type example: If I have an uneven kiln chamber, and one area is hotter than another area........ if I can "stall" the climb of the hotter area, and get the total heat input into the kiln chamber to equal ALL of the losses from that chamber, the hotter part of the kiln will get cooler and the colder part will get hotter until they reach a stage of equilibrium (even temperature distribution) whre it is equal in temperature everywhere. best, .......................john Got it. Thanks. Just wanted to make sure you were talking about heat not mass. (btw, water doesn't flow downhill unassisted, either, you need gravity for that .) Jim You got me on that lack of specificity . best, .......................john Link to comment Share on other sites More sharing options...
metal and mud Posted July 30, 2012 Report Share Posted July 30, 2012 I have always found it difficult to get good information on firing porcelain ... Most books are so vague that it almost makes it worse rather than better. I got Southern Ice at the first NCECA where free samples were offered and have been using it ever since ... Don't know how many years? I honestly still don't know if I am doing it right or not but over the years my process has certainly evolved ... with and without accurate help. I support all my pieces in forms made with a more durable high firing clay or with castable refractories. Porcelain slumps at high temps so you gotta give it support. I very seldom do, but if I am making wares for functional use I will glaze the top surface with a high firing clear glaze during that firing. Since it is supported, there is no way to glaze the bottom at high temps. That is why I would need a second firing at a lower temp that will not cause any slumping or warping. If I am only glazing for artistic effect, I don't really care about fit and I have found my Amaco commercial clears to be extremely forgiving. Right now I have a load of Cone 9 going through the controlled cooling phase of the firing. Controlled cooling is the best thing you can do for your work. A lot of firing problems occur on the way down, not up. My instances of warping and cracking dropped dramatically when I began to follow this cooling method. Why Cone 9 instead of 10 ... Because I personally cannot see any difference in the end product so why fire higher? I have a question/comment about controlled cooling as well. I use an old Paragon electric kiln with a sitter that is not electronic, so when the sitter flips, the temperature starts to drop. I can't control it. During a glaze firing over the weekend, which went well, I noticed that the temperatures dropped about 400 degrees in the first 90 minutes or so after Cone 6 was reached. Aside from getting digitally controlled kiln, which is out of the picture for now, is there anything I can do? Hi Chris: Great topic. Can you please clarify that you fire all of your pieces in formsto keep them from slumping? That is what I thought I read in your last post.This would seem to double the amount of ware that you have to heat in everyfiring. Is this the only way to keep your elegant forms from slumping? Also why don’t the forms slump? Also, can you expand on what you mean on controlled cooling? We fire to Cone 10in a gas kiln and let it cool naturally without any noticeable incidents ofwarping or cracking. I would be very interested though in knowing more aboutyour process and how you arrived at it. Thanks,,,, Link to comment Share on other sites More sharing options...
Red Rocks Posted July 30, 2012 Report Share Posted July 30, 2012 Because porcelain has no grog, it slumps and warps at high temps. Any form that spreads out from center ... like a bowl ... needs to be supported or it will sag. The support forms are made from a hardier, grogged clay that can withstand temps higher than my firing temp, so I am not pushing it to its limits at cone 9. The pieces dry in the form and fired in the form. If you use gas, I don't think you need controlled cooling ... it's mostly for electric kilns that cool much too quickly because of the thinner walls .... If this is wrong, someone please jump in! Many thanks...that helps Link to comment Share on other sites More sharing options...
metal and mud Posted July 30, 2012 Report Share Posted July 30, 2012 Because porcelain has no grog, it slumps and warps at high temps. Any form that spreads out from center ... like a bowl ... needs to be supported or it will sag. The support forms are made from a hardier, grogged clay that can withstand temps higher than my firing temp, so I am not pushing it to its limits at cone 9. The pieces dry in the form and fired in the form. If you use gas, I don't think you need controlled cooling ... it's mostly for electric kilns that cool much too quickly because of the thinner walls .... If this is wrong, someone please jump in! I posted a question about this that got inserted in the wrong place because of my lack of expertise. My old electric kiln--not digitally controlled for a slow cool-down--shuts off just fine, but the temperature drops very quickly. Can I do anything to stop this, other than replacing it with a digitally controlled kiln? Link to comment Share on other sites More sharing options...
Chris Campbell Posted July 31, 2012 Author Report Share Posted July 31, 2012 I'm not near my copy of it right now so I can't check but ... I think the "Mastering Cone 6 Glazes" book has some alternative solutions to controlling cooling without a computer. Anybody have a copy nearby to confirm? Link to comment Share on other sites More sharing options...
bciskepottery Posted July 31, 2012 Report Share Posted July 31, 2012 I'm not near my copy of it right now so I can't check but ... I think the "Mastering Cone 6 Glazes" book has some alternative solutions to controlling cooling without a computer. Anybody have a copy nearby to confirm? Their recommendation is to turn the kiln switches to medium for about 4 hours after you reach peak temperature. (page 144). Link to comment Share on other sites More sharing options...
metal and mud Posted July 31, 2012 Report Share Posted July 31, 2012 I'm not near my copy of it right now so I can't check but ... I think the "Mastering Cone 6 Glazes" book has some alternative solutions to controlling cooling without a computer. Anybody have a copy nearby to confirm? Their recommendation is to turn the kiln switches to medium for about 4 hours after you reach peak temperature. (page 144). Thank you so much!! That is very easy to do and it makes perfect sense. I need to get that book. I envisioned having to place a lead blanket on top of and around the kiln. . . Link to comment Share on other sites More sharing options...
SmartsyArtsy Posted July 31, 2012 Report Share Posted July 31, 2012 I fire ^6 electric with a controlled cooling from 1700 to 1350 which I found on http://www.wpapotters.blogspot.com/ . Since I began controlling the cooling I have noticed the Raspberry glaze I use is much richer (raspberry as opposed to deep pink). My kiln is small-- 18 x 23 and have no vent. I use a white stoneware ^04-6 and bisque to ^05. In 20 firings I have had no problems, but I am wondering if I should open the top peep for the first hour or 2 when glaze firing. I'm about ready to try a single fire. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.