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David Woodin

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Everything posted by David Woodin

  1. I neglected to ask you what controller you have. If it is the wall mount and old you may not have any options that allow you to review the offsets for T/C and cone and then that is why Skutt says you need new controller. David
  2. The Skutt Tech is correct in asking you to start with a new thermocouple. One of your problems will be to determine what the actual temperature is. Technicians have the means to determine this, a brand new thermocouple takes care of one variable. It will be interesting to see if there are any offsets applied to thermocouple or cone heatwork. I have never found the controller itself more than +,- 2 deg F which is well within spec's. Too bad you are not closer to the west, this is a very interesting problem. Another question, do you use self standing cones to check heat work? Making your own cone packs is okay if you read the fine print on how to set them, correct angle and depth. Self standing cones are always repeatable. Is the thermocouple an 8 gauge type K that is in a ceramic protecting tube? David
  3. There is no calibration of the thermocouple itself, but there is an offset adjustment which is usually one of the option keys on the front panel of the controller scroll to TCOS, the instruction manual tells how to increase or decrease the offset. It is best to just write down what the offset is set to for both the thermocouple TCOS and cone CNOS and think about it before making changes or call the Skutt technician. You can get into trouble. Cone offset increases or decreases the heatwork for each cone individually TCOS adjusts calibration of the temperature readings, and affects all cone numbers and user programs. David
  4. Neil is right and if your thermocouple was reading right cone 03 would have bent to about 30 deg with 1 hour soak @ 1920 deg F. If everything was correct than you only needed 1887 deg F for i hour soak to get cone 04 to 90 deg bend. So if you want to pursue this, short of getting someone like Niel to look at every thing you will have to talk to Skutt about what you can do. David
  5. True if the thermocouples are correct and no offset. The program to 1920 actually had more heat work than the program with no hold and a top temperature of 1945. You should look at how much offset the thermocouple has and /or play around with some hold time but not 1 hour hold. David
  6. Did you have a hold for the cone firing? Your own program had a 60 minute hold what was its last ramp to 1920 F? David
  7. I think you should rethink about your firing schedules for bisque and glaze. 85C is quite fast for the last step of glaze firing and if you are going this fast than the top temperature should have been 1230 C, but since you hold it for 15 min than the top temp is 1221 C Also depending on how good the elements are it is possible that the kiln can't fire this fast. Do you use self standing cones, or make your own cone pack? David I took the glaze firing schedule from digitalfire: http://digitalfire.com/4sight/firingschedule/mastering_glazes_cone_6_firing_schedule_83.html I usually use a more simple firing schedule: GLAZE: 120°C (248F) /h to 600°C (1112F) 135°C (275F) /h to 1230°C (2246F), soak 30 min. I have an electric kiln. which firing schedule do you use or recommend me to use? (I don't use cones, because the kiln seller told me they are not useful because the kiln is high performance and fires very precisely with the same temp all inside... but I will buy them now, that I understand I can reach cone 6 without necessarly reaching 1230°C (did I understand correectly?) Thank you :-) Bisque cone 06 48C ramp to 121 C hold 30 min, 149 C ramp to 538C hold 15 min., 65C ramp to 648C hold 10 min.,135 C ramp to 896 C hold 5 min., 26C ramp to 996 C hold 5 min. The big difference is slower through the carbon burnout period. Cone 6 glaze 93 C ramp to 93 C hold 15 min.,step to 1115 C hold 5 min., ramp 26 C to 1215 C hold 5 min., you can add your cool down if you like. The only way to be sure you are getting a cone 6 firing is to use witness cones after that you don't need to use them every time. I would recommend self supporting cones for witness cones. I hope things start to improve for you. David
  8. I would be inclined to change out the controller for a Barlett. The kiln itself will be fine but electronics have changed a lot in 22 years and you may be fighting problems due to drying out of compenents, parts no longer made etc. Euclids can help with getting you up to speed with a new Barlett and possibilily zone control. David
  9. I substituted Gerstley Borate for the colmanite in your glaze and made a 8 tile test and added the GB back into the glaze in 4 gram amounts, by tile 5=16 gram GB the surface was clear and glossy, tile 6=20 gram no blemish surface, tile 7=24 slight milkyness where thick no blemish, tile 8 some healed over pin holes, 8=28 grams. Self supporting cone 6@ 90 degree bend, clay laguna Amador stoneware. No faults at all. I don't know what this means in your case, clay? bisque not burning out the carbon material in clay? glaze firing too fast? Ware not dry enough after glazing to be fired? David
  10. My clay has 5% shrinkage on drying and another 5% on bisque the remainder on glaze firing. David
  11. There is a possibility that the bisque firing is not correct. With the speed of the last ramp plus 30 minute soak you are firing somewhere between C08 and C07. Also the program is too fast thru the carbon burn out area, 1000 deg F to 1100 deg F. The glaze program is also too fast for the last ramp. You should try to mimic the fixed programs in the manual for the kiln controller. David
  12. I think you should rethink about your firing schedules for bisque and glaze. 85C is quite fast for the last step of glaze firing and if you are going this fast than the top temperature should have been 1230 C, but since you hold it for 15 min than the top temp is 1221 C Also depending on how good the elements are it is possible that the kiln can't fire this fast. Do you use self standing cones, or make your own cone pack? David
  13. If you want to use less colemanite, or get B203 into limits. You could try Neph Sy 33,Wollastonite 15, colmanite 12, EPK 10, Silica 30. This has less fluxing power, but still is cone 6. David
  14. There is a lot wrong with this glaze. KNO low CAO high Al2O3 high B2903 high, also colemanite is a generic formula for Gerstley Borate. It would be better to supply B203 with a frit. You would have to abandon this glaze and start over or make a up a new formula and keep the formula within limits for cone 6. It probably spit because of the high amount of B203 supplied by colemanite. David
  15. "Clay and Glazes for the Potter" by Daniel Rhodes probably has what you are looking for. There is also another book that only using the percentage values. "Chinese Glazes" by Nigel Wood David
  16. No the fluxes don't have to add up to 100. You are to take a glaze and leave out the clay and Silica, if it has any, and just put in the flux material even though they may have some AL203 and SiO2 in them. Ex: Custer feldspar. The calculation on the web site is going to add clay and silica to the batch. I usually make test tiles because I want to see what happens on vertical surfaces. David
  17. You probably would do better by trying to hold the top temperature instead of cycling up and down. You can reglaze the pieces and fire again with a hold. I didn't think that clay was used in the ancient recipes. David
  18. Probably some of my materials are not up to date.. Tea using Matrix, all within limits, Green and Cooper in limits, Food safe Alumina okay, Silica too high, Insight Alumina too high SI okay MGO high KNO low B203 low. Speckles, Matrix AL okay Si on the edge of being too high, Food Safe AL too high Si on the edge, Green and Cooper B203 on the edge of being high, Insight AL and Si high B203 low MGO high KNO low. So it is best to use what you are satisfied with. David
  19. Sorry, before looking at the pictures I though you were talking about teadust. MGO will produce teadust in some glazes. The speckles glaze is on the AL/SI outer limits and B203 is quite high. Both glazes use a lot of different materials. They both could be modified so that you would not have to stock so many materials. Neither is in the food safe limits. I am not much help. David
  20. It is the talc in the glaze. David
  21. I use Matrix limits, Insight limits, and Food safe Cone 6, Cone 10 limits. Insight and Matrix allow for cones other than Cone 6 and Cone 10. I usually fire to cone 7 in the electric kiln and in the gas kiln cone 9. That way I only need one stoneware clay body. David
  22. Matrix does have the Currie grid and also you can make your own grid. I make my own grid and make the corners match the Al/Si limits for whichever cone I am firing at. Matrix also has a very good method for testing colors used in glazes. David
  23. On www.efcouk.com it shows the termocouple and read out device for your kiln , part # 99 502 41 page 11. David
  24. Assuming that you are firing thrown ware, for me this program is too slow. If I fire bisque with the bisque program, I use fast bisque no hold. If I fire with my own program , it is ramp @ 200 to 200 hold 30 minutes, ramp 300 to 1000 hold 5, ramp 250 to 1200 hold 10. step to 1680 hold 5, ramp 80 to 1830 hold 10, off. I bisque at 06. If I think things are not bone dry I use the preheat and hold10 to 30 minutes. David
  25. You will have to change the plug on your kiln to fit into the regulator, but the regulator also has the wrong plug for your UK receptacle. I would find an electrician who can help on this. You don't need a thermocouple but it will be a great help. As mentioned before the cones only show what happened after the firing. The temperature indication will give you an idea as to whether the kiln is rising or stalled or too hot. David
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