Pieter Mostert Posted December 16, 2014 Report Share Posted December 16, 2014 Firstly, let me say that I know this question probably can't be answered with any confidence, so I'm just looking for educated guesses. I've attached a picture of two cone 4 cones from my last glaze firing (the first in a used kiln). Based on the results of the bisque (cone 08 flat at what should have been between 09 and 08 according to the controller), I knew that the temperatures displayed by the controller were less than the actual temperatures, but clearly under-estimated the difference at higher temps. I'm pretty sure I went over cone 5, since the cones are on their way to melting, but I'd like to know how close this looks to cone 6. Before anyone tells me I should have used 3 cones (3,4 and 5), I know. I had my reasons, which were probably not very good. My kiln fired quite slowly towards the end of the firing - it took about an hour for the last 30 degrees C (54 degrees F), and the last 100 degrees C took about 2 and a quarter hours. I didn't soak at the end. So... if I reached cone 6 (or whatever), what was the max temperature? I know I could look at the cones during the firing and work out how far off the thermocouple is that way, but I don't think it's worth getting welders glasses, so I'm just going to do this by trial and error, and hopefully a little help from you folks. Link to comment Share on other sites More sharing options...
Chris Campbell Posted December 16, 2014 Report Share Posted December 16, 2014 I'm not going to crab at you because I have done these kinds of things too. My guess would be about Cone 6. Since Cone firing is a combination of time and temp it is anyone's guess what temp you were at. It would be cheaper and much less stressful to buy witness cones instead of firing by the seat of your pants time after time ... but you know that already!! Link to comment Share on other sites More sharing options...
neilestrick Posted December 16, 2014 Report Share Posted December 16, 2014 Yeah, about cone 6. Link to comment Share on other sites More sharing options...
Crusty Posted December 16, 2014 Report Share Posted December 16, 2014 Yea you floored those cones and with the smaller one in there, i agree with CC. if you are using Orton cones , each size has a different melting temp.. i have a chart somewhere.. Ahhhh found it... Orton Pyrometric Cone Chart (Degrees Fahrenheit) Cone NumberSelf Supporting ConesNormal Large ConesSmall Cones 0221087Not Available1166 0211112Not Available1189 0201159Not Available1231 019125212491333 018131913141386 017136013571443 016142214161517 015145614501549 014148514851598 013153915391616 012158215761652 011160716031679 010165716481686 09168816831751 08172817281801 07178917831846 06182818231873 05 1/2185918541909 05188818861944 04194519402008 03198719872068 02201620142098 01204620432152 1207920772163 2208820882174 3210621062185 4212421202208 5216721632230 5 1/221972194Not Available 6223222282291 7226222591307 8228022772372 9230022952403 10234523402426 11236123592437 12238323792471 1324282410Not Available 1424892530Not Available Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted December 16, 2014 Report Share Posted December 16, 2014 I would say 1-2 cones but I have never fired a cone further than 2 cones higher. I don't know what they tend to look like 3-5 cones over fired. Saying that my cone 8's look similar to that when I am firing to 9.5/10. Maybe try taking half an hour off the firing time and see what cone/temp it gets to. Link to comment Share on other sites More sharing options...
Marcia Selsor Posted December 16, 2014 Report Share Posted December 16, 2014 I would say 1-1.5 cones above the cone you were using. It is not that puddled. Marcia Link to comment Share on other sites More sharing options...
neilestrick Posted December 17, 2014 Report Share Posted December 17, 2014 If your kiln took an hour for the last 50 degrees, that's pretty slow. I'd check to see if your elements are worn, of if your kiln isn't rated for cone 6. At that slow a rate of climb, the temperature for cone 4 will be quite a bit lower than the slowest (108F) rate of climb shown on cone charts. Cones measure heat work, which is dependent on the rate of climb. You've got to watch the cones bend to know for sure. Link to comment Share on other sites More sharing options...
Mark C. Posted December 17, 2014 Report Share Posted December 17, 2014 (but I don't think it's worth getting welders glasses, so I'm just going to do this by trial and error) it is worth it to by the protective eyeware-its not much$$ and you will need to view the cones to know anything about where the temps are as far as glaze work.You absolutely need to see the cones thru the spy ports. Without the visual view of cones it will be all error. Mark Link to comment Share on other sites More sharing options...
Pieter Mostert Posted December 17, 2014 Author Report Share Posted December 17, 2014 Thanks for all the feedback. I now have a better guestimate of what temperature (as reported by the controller) to fire to. I'm firing today, and am using cones 3, 4 and 5, so even if I don't hit cone 4, I'll have a better idea how to adjust the firing next time. Link to comment Share on other sites More sharing options...
Lockley Posted December 17, 2014 Report Share Posted December 17, 2014 Pieter, I really think if you go to your welding supplier you will find that the glass inserts used in welding helmets are very inexpensive. Most welding suppliers also have a selection of dark polycarbonate "sun glass" style safety glasses that welders and people that work near them use when not directly performing welding operations. I say this as long time member of ABANA (Artist-Blacksmith's Association of North America) One of the key safety issues for long term Forge/Kiln/Glass workers is the exposure to, not only ultraviolet radiation. but also long wave infrared radiation. The damage that the eyes receive from high temperature exposure is cumulative. I hope you have a lovely holiday and a safe New Year. Lockley Link to comment Share on other sites More sharing options...
S. Dean Posted December 17, 2014 Report Share Posted December 17, 2014 Pieter, I really think if you go to your welding supplier you will find that the glass inserts used in welding helmets are very inexpensive. Most welding suppliers also have a selection of dark polycarbonate "sun glass" style safety glasses that welders and people that work near them use when not directly performing welding operations. I say this as long time member of ABANA (Artist-Blacksmith's Association of North America) One of the key safety issues for long term Forge/Kiln/Glass workers is the exposure to, not only ultraviolet radiation. but also long wave infrared radiation. The damage that the eyes receive from high temperature exposure is cumulative. I hope you have a lovely holiday and a safe New Year. Lockley I believe that Lockley is referring to something like this. This design is made to go over prescription glasses and comes in shade 3. There is another model which comes in shade 5 which offers more protection to your eyes. However, I recall that many potter's find Shade 5 too dark. http://www.envirosafetyproducts.com/uvex-ambient-over-the-glass-safety-glasses-shade3-0.html Link to comment Share on other sites More sharing options...
Pieter Mostert Posted December 17, 2014 Author Report Share Posted December 17, 2014 Thanks for the info on glasses. They aren't as expensive as I imagined. However, my main reason for not getting glasses is that my kiln has a controller, so if I can adjust for the error in the temperature reading, I won't need to watch the cones during the firing. I don't think it's worth getting glasses just to figure out the error, and then fire with the controller from then on. Of course, this is all assuming the error is consistent from firing to firing, but if it isn't, I need to get a new thermocouple. Actually, the controller is crappy in other ways, but that's a topic for later. Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted December 17, 2014 Report Share Posted December 17, 2014 It could be reading the right temperature but taking too long to get there. On your controller how do you program in the ramps? Does the last ramp go full power to a set temperature or can you choose how many degrees it climbs per hour? Link to comment Share on other sites More sharing options...
Wyndham Posted December 17, 2014 Report Share Posted December 17, 2014 old thermocouples lose integrity as they age and it maybe the T?C is wore out and not reading the proper temp. if this is the case you need to change the t/c. several things could give this result, t/c and or elements Wyndham Link to comment Share on other sites More sharing options...
neilestrick Posted December 17, 2014 Report Share Posted December 17, 2014 If your controller is that far off, then either the thermocouple is worn, or there's something wrong with the calibration, or both. Are you programming it to fire to a specific temperature, or to a specific cone? If you're firing to a temperature, then you have to figure out what that temperature is for your desired cone as it relates to the rate of climb. If your controller kiln can't keep up with the programmed rate of climb, then you won't hit the desired cone at the programmed temperature. If you can't trust the kiln or controller, then watch the cones. Guesstimating will only give you more bad firings. A controller is no good if it doesn't give you the results. Plus, when you change the thermocouple in the future, you'll have to start all over with your estimates. Link to comment Share on other sites More sharing options...
Crusty Posted December 18, 2014 Report Share Posted December 18, 2014 It may help you to use the same size cones as well.. you will get better results , your Large cone is at 2120 F your small cone which is usually used in kiln sitters is 2208 F - I fire to cone 6 and 8 and always use a Large cone in the kiln to view and a small one in the sitter, when the small cone melts and trips the sitter off I know the heat work is done... Link to comment Share on other sites More sharing options...
Pieter Mostert Posted December 18, 2014 Author Report Share Posted December 18, 2014 I can program the rate of temperature increase, but above a certain point the kiln can't go more than 60 degrees C per hour, which is the rate at which I program the last 100 degrees to be fired at. I do this to be able to use Orton's cone chart to calculate the top temperature. When I decided on what temperature (on the controller) to fire to yesterday, I tried to take the slowing down into account, both in estimating the actual temp I reached the first time, assuming I fired to cone 5.5, and the actual temp I needed to fire to to hit cone 4. Whatever errors I made seem to have mostly cancelled out, as you can see by the cone pack.I'm pretty sure the thermocouple is worn, and it's quite possible that it's never been replaced. It may also be that it was slightly damaged when it was moved. I will need to replace it at some point, but for now it looks like I can just adjust for the error. When I do replace it, it seems reasonable to expect that I won't have to do any adjustments to begin with. I plan to have cones in the kiln for every firing, so if the error gradually increases I can adjust for it accordingly.I should add that it isn't essential for me to be that precise about what cone I fire to, since I'm not glazing my pots at the moment, and the only utilitarian things I make are planters.Crusty, you're using the temperatures for a large cone fired at 108 degrees F per hour, and a small cone fired at 540 degrees F per hour. As I understand it, if they were fired at the same rate, they would bend at the same temperature. Link to comment Share on other sites More sharing options...
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