Nelly Posted July 31, 2012 Report Share Posted July 31, 2012 Dear All, Just a short note to let you know two things I learned today that may not be new knowledge to all on the forum. We all know in general that clay should not be put into an electric kiln if it is not dry. Bone dry. Warm to the face. But there have been occasions in my past studio using a kiln sitter whereby I simply candled my work for 3-4 hours to make sure as much water is driven off as possible. Apparently with digital controlled machines you can ruin your elements or thermocouple quicker the longer you leave it on this constant temperature (i.e., 180 degrees). It is something about the sensor constantly clicking on to check to see that the temperature in the kiln is correct. This can lessen the life of this mechanism. The second is we all know that it is best to leave a kiln until it is finished cooling before opening the lid to prevent thermal shock. I normally in my old kiln sitter kiln would open the peep holes at 350 and wait and hour or so and then crack the lid with a brick to gently let some of the heat out to get into the kiln a little more quickly. Anyway, in speaking with my pottery supply company they said "wait and do not open until it is right down especially with large flat platters." In my reading today, I found that digitally controlled machines can have a tendency to have ware break more readily if it is cracked early (i.e., oven temperatures). It has something to do with sudden drafts from the vent and/or elements. Thought I would pass this along. I think if this is true that I am not sure all potters with these types of kiln know this or am I the only one?? Nelly Link to comment Share on other sites More sharing options...
bciskepottery Posted July 31, 2012 Report Share Posted July 31, 2012 The clicking sound you hear is from the relays that provide the flow of electricity to the elements that build/maintain heat. The thermocouplers measure temperature and let the relays know when they need to turn on/off. At the studio where I loaded kilns, we generally "candled" the electric kilns w/computer controllers for 2 hours to make sure things were dry. Sculpture and other large, thick items were "candled" longer . . . sometimes up to 12 hours if we were unsure of the dryness of a thick piece or piece of sculpture. The top was generally propped open until the kiln completed its "candling" to allow any steam to escape and evaporate. Can I ask what the source is for the statement that digitally controlled kilns have a tendency to have ware break more readily if cracked early? Link to comment Share on other sites More sharing options...
Nelly Posted July 31, 2012 Author Report Share Posted July 31, 2012 The clicking sound you hear is from the relays that provide the flow of electricity to the elements that build/maintain heat. The thermocouplers measure temperature and let the relays know when they need to turn on/off. At the studio where I loaded kilns, we generally "candled" the electric kilns w/computer controllers for 2 hours to make sure things were dry. Sculpture and other large, thick items were "candled" longer . . . sometimes up to 12 hours if we were unsure of the dryness of a thick piece or piece of sculpture. The top was generally propped open until the kiln completed its "candling" to allow any steam to escape and evaporate. Can I ask what the source is for the statement that digitally controlled kilns have a tendency to have ware break more readily if cracked early? Dear Bciskepottery, I heard it from my pottery supplier. I also took some time today to google it. Now I can't find my source. I know a piece can never really be thoroughly dry and I have in the past done candling to ensure that as much of the water is driven off. My interest was in the issue of the possibility of ruining my kiln in some way. That was the focus of my search. Also, when I told my supplier my firing schedule which is the one on the Frog Pond site that he recommended he said "don't open it until tomorrow morning." By this he meant Tuesday morning. That would add up to a cooling period of 24 hours. He was most insistent on this and repeated it three times to me. I know he has had pieces break and I am guessing it was his experience that was speaking. My schedule started last night (Sunday at 7pm). It finished at roughly 7am this morning. It has been cooling all day. I looked up problems with opening the kiln early. I found a source somewhere on the Internet that said if you have shallow dishes or flat plates, any draft from a vent could break these pieces due to thermal shock. This of course can happen in any kiln but somewhere I read it about what I thought I saw as a digital controlled issue. Having said this, given that I can't find my source as I retrace my steps from today, I could be wrong?? Maybe it was meant for all kilns?? But again, it is interesting that my supplier said it three times to me to instill in me the importance of going really slow. My kiln is packed with shallow bowls, flat pieces, vases, small sculptural work. I just found it interesting as I too have had a large piece break when they never did before at removing ware at 300-350 in this kiln. Thus, my research. Does the candling part make sense to you?? Could it cause the kiln relay to break down more readily with the constant checking of temperature during a long session such as you described? Nelly Link to comment Share on other sites More sharing options...
bciskepottery Posted July 31, 2012 Report Share Posted July 31, 2012 Relays are mechanical devices; at some point they do wear out . . . but that wearing out could come as easily from a controlled cooling firing program as from candling, or a combination of both. And some relays seem to last longer than others. Of the three most often replaceable kiln components (thermocouplers, elements, and relays), relays are the cheapest -- if that is much consolation. Personally, I hold off opening/unloading until the kiln has cooled to around 100 degrees F -- bisque and glaze. I fire an electric kiln with computer controller; my vent is turned on when I start firing and is turned off when its time to unload. Even though the temperature of the atmosphere in the kiln may be 100 (or pick a temperature), the wares (and kiln shelves) may be hotter and hold heat longer. Shallow forms, because they sit on a larger surface area of the kiln shelf, are likely to retain heat and be hotter than the temperature reading. Link to comment Share on other sites More sharing options...
Nelly Posted July 31, 2012 Author Report Share Posted July 31, 2012 Relays are mechanical devices; at some point they do wear out . . . but that wearing out could come as easily from a controlled cooling firing program as from candling, or a combination of both. And some relays seem to last longer than others. Of the three most often replaceable kiln components (thermocouplers, elements, and relays), relays are the cheapest -- if that is much consolation. Personally, I hold off opening/unloading until the kiln has cooled to around 100 degrees F -- bisque and glaze. I fire an electric kiln with computer controller; my vent is turned on when I start firing and is turned off when its time to unload. Even though the temperature of the atmosphere in the kiln may be 100 (or pick a temperature), the wares (and kiln shelves) may be hotter and hold heat longer. Shallow forms, because they sit on a larger surface area of the kiln shelf, are likely to retain heat and be hotter than the temperature reading. Dear Bciskepottery, I have been turning my vent off just as soon as my kiln goes off. Perhaps I should be leaving this on longer. Anyway, I am a bit embarrassed by not being able to find the site on the net that confirmed what my supplier told me. Either way, I am sure I have learned something (i.e., not removing stuff until it is really cool). I did have a lot of pinging with my last bisque firing. Thank you for writing and contributing to my thinking for the day. And yes, it is some consolation to know that relays are the cheapest. Nelly Link to comment Share on other sites More sharing options...
Mark C. Posted July 31, 2012 Report Share Posted July 31, 2012 I'm always pushing the limits of what can be done . For example last week I threw a run of mugs handled them and loaded them into a bisque and fired them overnight in gas kiln along with 40 cereal bowls I threw and trimmed all same day. This can be done if you slow down the firing cycle to allow for the drying of wares during candling. For me the sun needs to be out to dry the pots enough to trim and or handle. I have felt for a long time (30+years) that my electric can fire wetter pots than my gas kilns as I can control the heat on a gradual rise. Let me 1st say the kiln is a medium large skutt that I have added a fire right ramp up control box. That is the kiln switches are always set to high and you set the ramp knob in hours to when the elements are on full . The cone sitter turns the thing off along with a timer for backup . I have loaded many a wet load of ware and set the controller to 6-8 hours and kept the lid cracked till the steam is gone without any worries to blown up wares. I know its harder on the elements but I do not care as the replace easy. On the other end I do not have a kiln/fan vent as I only use this for bisques and its outside. I will crack the lid 1/2 inch at 600 if in a big rush and slowly over time get the lid wide open and let the heat out top . All holes are plugged tight and have never had an issue with my porcelain bisque. . this wild cycle usually only happens in December when I'm pushing all the limits of production. As stated its harder on elements but I'll just replace when needed and mine are still all original from the late 80's on this kiln. under normal times I fire dry pots and let cool to 200 before lid cracking on bisque. I let my gas kiln cool for two days unless I really need the pots. You will never know what is the limit of things if you do not push them to find out.I am known to push the limits . Mark Link to comment Share on other sites More sharing options...
DAY Posted July 31, 2012 Report Share Posted July 31, 2012 Some 'Newbies' may not know the trick of holding a mirror above the top peephole. If it fogs, there is still moisture coming out! As to "rules" of when to open, etc, there are too many clay/glaze variables for a one size fits all answer. Better to be so busy with other tasks that you forget to open the kiln until tomorrow! Note: this is NOT a rule- with a show to pack for you can usually open the kiln, unload with oven mitts and pack for the show as soon as the ware doesn't melt the bubble wrap. Link to comment Share on other sites More sharing options...
neilestrick Posted July 31, 2012 Report Share Posted July 31, 2012 A digital kiln will not crack pots any more than a manual kiln. If you have a vent, it could cause the kiln to have a bit more draft than without, but that has nothing to do with the kiln being digital or not. Both types of kilns cool at the same rate. As for preheating or candling with digital kiln, yes, it can shorten the life of your relays since they will be clicking on and off more. But relays wear out regardless, and they are relatively cheap and very easy to fix. Much cheaper than blowing up a bunch of pots. Other than that, preheating will not do any damage to your kiln, and will not really affect the life of your elements. Temperature affects them far more. Link to comment Share on other sites More sharing options...
Nelly Posted July 31, 2012 Author Report Share Posted July 31, 2012 A digital kiln will not crack pots any more than a manual kiln. If you have a vent, it could cause the kiln to have a bit more draft than without, but that has nothing to do with the kiln being digital or not. Both types of kilns cool at the same rate. As for preheating or candling with digital kiln, yes, it can shorten the life of your relays since they will be clicking on and off more. But relays wear out regardless, and they are relatively cheap and very easy to fix. Much cheaper than blowing up a bunch of pots. Other than that, preheating will not do any damage to your kiln, and will not really affect the life of your elements. Temperature affects them far more. Dear All, Thank you one and all for your replies. In looking over the responses it seems I got bits of new information yesterday and other parts that were no different from my other knowledge. I too push the limits on things but in general they are not technical but have to go with glaze combinations. When it comes to the kiln I treat it with the up most respect. Sounds like if I want I can still candle. While relays can burn faster--they are cheap. That is the good news. I also took note of the mirror suggestion. Great idea. It does make perfect sense. Finally, I got Neil's message clearly. Warping or breaking has zippidy doo dah to do with digital kilns. And yes, they were talking about the vent system for breakage. Good strong advice. In conclusion, I did wait to take all the ware out this morning. All work turned out well. Large platter seems flat and no cracks. Shallow bowls were great. Sculptural pieces made it. Some pin holes but nothing huge. I did get some metal like shine from one potter's glaze I had been experimenting with. I think in retrospect my past practice of cracking early and opening the peep holes is not be in my best interest given my few short years of firing and now getting used to this new kiln. I have decided for me that I will now wait. I had no pinging this morning. The vessels were still warm to the touch but all and all, were fine. When you wait, you don't have to worry as much. As was said before, the shallow dishes absorb more heat due to the surface area covered on the floor of the shelf. Makes sense. Thank you again to each of you for replying. I really appreciate all of your help. In looking back over my original responses from last night I can see the influence of the Netflick I am currently watching "Breaking Bad" as I talk about my "supplier." Nelly Link to comment Share on other sites More sharing options...
yedrow Posted July 31, 2012 Report Share Posted July 31, 2012 I've fired tons of bisque by cracking at 500 and opening at 300 without ever having a problem. If the pore water is out you can put your pots on top of a hot kiln and drive the rest of the water out quick. As far as my experience goes, once the stuff has lost its plasticity you can stick a fan on it even. Nice work Mark. You must throw some thin stuff and your handles must have a low profile where you stick them. I'm gonna see if I can get a load out in a 24hr cycle now! My big concern will be where the upper part of the handle sticks. It's a long way to the center of the mass there. Link to comment Share on other sites More sharing options...
Mark C. Posted August 1, 2012 Report Share Posted August 1, 2012 Yedrow, The trick is porcelain clay as it drys so fast-I'm not making them that thin but the key is the handles go on when the mugs are almost to wet to handle-just past that point-other wise they will crack a tad at the top attachment point. On this table of a zillion mugs from the last fire are about 30 mugs that I spoke about-they all made it fine -They are all priced and packed now and some are already in galleries now. Those where 1# mugs I quick bisqued. Link to comment Share on other sites More sharing options...
morah Posted August 1, 2012 Report Share Posted August 1, 2012 Some 'Newbies' may not know the trick of holding a mirror above the top peephole. If it fogs, there is still moisture coming out! As to "rules" of when to open, etc, there are too many clay/glaze variables for a one size fits all answer. Better to be so busy with other tasks that you forget to open the kiln until tomorrow! Note: this is NOT a rule- with a show to pack for you can usually open the kiln, unload with oven mitts and pack for the show as soon as the ware doesn't melt the bubble wrap. I'm one of those newbies who doesn't know about the mirror trick. Not only that, I am such a newbie that I don't understand the significance of moisture coming out. What does this mean in terms of the cycle of firing- at what point does moisture come out? What does this mean in terms of keeping the peepholes open/shut? Can you kindly elaborate? Thanks- I really appreciate your giving of your time and experience to help newbies like me. Link to comment Share on other sites More sharing options...
yedrow Posted August 1, 2012 Report Share Posted August 1, 2012 Morah, there are several types of water in clay. There is the surface water you drip on it etc., the pore/interstitial water that lies between the particles (when this water leaves the clay shrinks), and there is bound water that coats the individual clay particles (kind of making them like little gelatinous balls that slide against each other). In pieces of thicker ware all of this water needs to be driven out. The 'skin' of the clay will tighten up as the pore water and bound water leave it. This slows the movement of water from the interior of the body and into the atmosphere. Feeling dry isn't dry. When the interior water is out the generation of steam should end and water should quit condensing on the mirror when you put it above the peep hole. You then have to go somewhat slow through the alpha-beta inversion, and then slow when the 'water of smoking' (chemically bound water) and organics/sulfer are volatized. I bisque at about 180/hr. after passing 212 (boiling point). Joel. Link to comment Share on other sites More sharing options...
Frederik-W Posted August 1, 2012 Report Share Posted August 1, 2012 You can pre-dry things quite a lot without electricity, by the sun or with a wind/draft. This seems common sense but somehow people do not take enough advantage of it. Be carefull of putting it in direct sunlight too soon though - the sun can be very hot and you can get cracks. Turn your pots around so that you dont get the sun shining only one one side. A fan can also help to dry things out. An incandescent bulb near the work dries out the air and causes a slow upward draft. You can also use a small heater. I think its best to start slowly with above things and then speed up the drying process. Link to comment Share on other sites More sharing options...
neilestrick Posted August 1, 2012 Report Share Posted August 1, 2012 So yesterday I trimmed a few porcelain pitchers that I need for this weekend. Immediately after attaching handles I put them in my small electric kiln and did a 4 hour preheat to dry them out, then ran the bisque on the Fast Glaze setting to cone 04, which only took 4 hours. It's noon now, and they're ready to come out of the kiln. So only 20 hours to dry, bisque fire and cool down. Not bad. Porcelain handles actually hold better and pull away less if you speed dry the pots, I think because they dry more evenly when they dry really fast. I almost always speed dry my pitchers in the kiln nowadays. Link to comment Share on other sites More sharing options...
Nelly Posted August 1, 2012 Author Report Share Posted August 1, 2012 So yesterday I trimmed a few porcelain pitchers that I need for this weekend. Immediately after attaching handles I put them in my small electric kiln and did a 4 hour preheat to dry them out, then ran the bisque on the Fast Glaze setting to cone 04, which only took 4 hours. It's noon now, and they're ready to come out of the kiln. So only 20 hours to dry, bisque fire and cool down. Not bad. Porcelain handles actually hold better and pull away less if you speed dry the pots, I think because they dry more evenly when they dry really fast. I almost always speed dry my pitchers in the kiln nowadays. Dear Neil, Wow!! That is fast and it shows knowledge of how far you can stretch your clay (no pun intended). You understand what the clay will do under what circumstances. I guess that it why it really pays to stick to one type of clay. I tend to bounce around from low fire to medium firing bodies. No porcelain. Stone and red ware mostly. But the principals are the same if you know what you are doing...I think. Nelly Link to comment Share on other sites More sharing options...
Edith Marie Posted August 1, 2012 Report Share Posted August 1, 2012 Dear All, Just a short note to let you know two things I learned today that may not be new knowledge to all on the forum. We all know in general that clay should not be put into an electric kiln if it is not dry. Bone dry. Warm to the face. But there have been occasions in my past studio using a kiln sitter whereby I simply candled my work for 3-4 hours to make sure as much water is driven off as possible. Apparently with digital controlled machines you can ruin your elements or thermocouple quicker the longer you leave it on this constant temperature (i.e., 180 degrees). It is something about the sensor constantly clicking on to check to see that the temperature in the kiln is correct. This can lessen the life of this mechanism. The second is we all know that it is best to leave a kiln until it is finished cooling before opening the lid to prevent thermal shock. I normally in my old kiln sitter kiln would open the peep holes at 350 and wait and hour or so and then crack the lid with a brick to gently let some of the heat out to get into the kiln a little more quickly. Anyway, in speaking with my pottery supply company they said "wait and do not open until it is right down especially with large flat platters." In my reading today, I found that digitally controlled machines can have a tendency to have ware break more readily if it is cracked early (i.e., oven temperatures). It has something to do with sudden drafts from the vent and/or elements. Thought I would pass this along. I think if this is true that I am not sure all potters with these types of kiln know this or am I the only one?? Nelly Link to comment Share on other sites More sharing options...
Edith Marie Posted August 1, 2012 Report Share Posted August 1, 2012 Hello Nelly. I found your tip interesting because I have a Skutt manual and I always candle over night or about six hours then I turn the knobs to medium for an hour then turn them to high until the kiln sitter melts and my kiln shuts off. I also wait two days before I unload. This procedure is working for me but now I am second guessing if this is right.......any comments are appreciated as I am a newbie just having fun making and glazing.... Link to comment Share on other sites More sharing options...
neilestrick Posted August 1, 2012 Report Share Posted August 1, 2012 If I had put stoneware pots in my kiln to speed dry, it would have taken longer by a at least a few hours. Porcelain dries faster, since it has a lower clay content. Fine grained white stonewares and buff bodies that are high in ball clay take forever to dry by comparison. Either way, once they are dry there's no worry of them blowing up and the firing can go pretty fast. There is so much variability in every part of the ceramic process that there are no hard and fast rules. Some things work well for some people, but not others. Don't be afraid to push the limits to see what you and your clay can handle. I often crack the lid of the kiln on my bisque firings at 500 degrees if I'm in a rush. I try to avoid it if I've got some 15 pound jars in there, because they could crack, but for smaller stuff it's not a problem. If your pots are totally dry, a 4 hour bisque firing will work just fine most of the time. But if you've got a clay body with a lot of sulphur and junk in it it could cause pinholing or other problems in the glaze firing. Most of the 'rules' and guidelines we hear concerning firing times and cooling rates and when to crack the kiln are the safer way to go, if you don't want to risk problems. But sometimes they are safer than necessary and the process can be sped up quite a bit with no problems. As we always say, test, test, test..... Link to comment Share on other sites More sharing options...
Nelly Posted August 1, 2012 Author Report Share Posted August 1, 2012 Hello Nelly. I found your tip interesting because I have a Skutt manual and I always candle over night or about six hours then I turn the knobs to medium for an hour then turn them to high until the kiln sitter melts and my kiln shuts off. I also wait two days before I unload. This procedure is working for me but now I am second guessing if this is right.......any comments are appreciated as I am a newbie just having fun making and glazing.... Duckie, Given that we are fairly new at this art, I am now of the opinion to wait. Wait the 24 hours. I had no pinging sounds yesterday when I removed my ware. I think you are wise to wait the two days. But, like Mark, I have also seen myself pushed to the limit in trying to get work completed for a show using a manual kiln. I remember once taking work out early (i.e., say 400-500) and wrapping each shelf of work in sleeping bags to sort of gently cool off the work in a way where the heat would still be there but it would not face thermal shock. Know I did not do this on my own but was instructed by the studio head to do this way to get all members work completed in time for the show. Not a great way to do things but all and all everything did turn out okay without any glaze problems. So yeah, you are smart I think now to wait--especially given the infancy of our knowledge about doing this process independently. As for the candling, I too used to love this process. It gave me a sense of confidence to know that as much water as possible was driven off. I also, in my last studio did not pay the hydro bills so I could candle away. One thing that is important I think is to keep all peep holes open during this process to really get rid of the water on all levels. I am not sure if everyone does this but that was my practice. Nelly Link to comment Share on other sites More sharing options...
neilestrick Posted August 1, 2012 Report Share Posted August 1, 2012 Good point. Keep the peeps open or run your vent so the water vapor can escape during candling. As for cost, the price of candling a round electric kiln overnight will cost you less than a dollar. It's a very small price to pay for preventing explosions. For glaze loads, I won't crack the kiln until it gets down to 300. It's much touchier than a bisque load. If you don't have a thermocouple on your kiln, stuff a piece of paper in the spy hole. It will start to smolder at around 400 degrees. If it's below 400, pull the peeps. A few hours later, crack the lid. Link to comment Share on other sites More sharing options...
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