Dick White

Mea, this is a interesting recipe that shows up in a variety of places. The version you have is very close to one that we have been using in the Audrey Moore/Wakefield (Ffx County Parks) studio since forever.  That one is Gerstley 50, EPK 17.5, Silica 32.5 (our Gerstley vs. your 3134, about the same effect; your EPK and silica are reversed from ours). From a chemistry standpoint, the massive amount of Gerstley or 3134 generates so much boron that it could/should be a low-fire glaze - and indeed I have seen it in published collections of earthenware glazes. At the same time, the alumina and silica levels are quite high, and so the glaze is robust enough to survive at cone 6. With the demise of Gerstley, I am reformulating it to use 3134, and my revised recipe becomes similar to yours. Something to consider - 30 EPK is a lot to have in a recipe, and will cause issues with shrinkage and cracking (leading to crawling during the firing) so replace half of it with calcined EPK. It just so happens right now I have a test tile with my revised recipe soaking in vinegar, so I will come back in a day or so with the outcome of that.

oops, I take all that back. I just looked for the log file when I first noticed the timer can only show 24 hours, and indeed as you said, there are 2 files - one showing the first 24 hours of the preheat hold and another picking up right from there through the end of the firing.

Yes, I use either a prior 5-minute or 10-minute rolling average. If you did that, you would see exactly where the elements begin to falter in mid-segment as the temperature increases, and how bad it gets as the firing progresses.

They are discrete .csv files that must be appended together in your program.

In senior times, teeth are falling out, not growing in. Don't ask how I know this. The difference between the two lines is attributable to his skip segment during the initial preheat hold. If you mentally extend that flat section of the blue line so that both lines concur at the first serious ramp up (i.e., move the blue inflection at minute ~80 to match the green inflection at minute 180), the two lines will be close up until ~1800 degrees. At that point, the slope of the blue line in segment 5 should continue straight until a distinct inflection at the beginning of segment 6 (as shown on the green line) but instead the ramp rate begins to falter, likely due to somewhat worn elements. There is not a distinct inflection in the blue line at the ramp change for the beginning of segment 6, instead it gently curves from one to the next. Even with the programmed slower ramp rate in segment 6, the kiln isn't keeping up. The slope of the blue line, while steady, is slightly lower than the slope of the green line and the blue segment 6 takes a bit longer to complete than the green. These are the kind of diagnostics that I find such graphs to be helpful.

In senior times, teeth are falling out, not growing in. Don't ask how I know this. The difference between the two lines is attributable to his skip segment during the initial preheat hold. If you mentally extend that flat section of the blue line so that both lines concur at the first serious ramp up (i.e., move the blue inflection at minute ~80 to match the green inflection at minute 180), the two lines will be close up until ~1800 degrees. At that point, the slope of the blue line in segment 5 should continue straight until a distinct inflection at the beginning of segment 6 (as shown on the green line) but instead the ramp rate begins to falter, likely due to somewhat worn elements. There is not a distinct inflection in the blue line at the ramp change for the beginning of segment 6, instead it gently curves from one to the next. Even with the programmed slower ramp rate in segment 6, the kiln isn't keeping up. The slope of the blue line, while steady, is slightly lower than the slope of the green line and the blue segment 6 takes a bit longer to complete than the green. These are the kind of diagnostics that I find such graphs to be helpful.

The mini-cones and pyrometric bars are more-or-less equivalent. Some would argue that the bars are more accurate, in that they cannot be shifted to one end or the other to slightly change the outcome, but if her bars are 018 or 019, they will be fine for your work.

PM me if you want a printable copy of the Mason reference guide. ( I converted it to a pdf for my glaze chem class notebook)

I suggested to Ron in a PM that we drop the testing idea for the time being. Pacer ceased operations as of Nov 1, so Custer has just joined the ranks of unobtainium. Their announcement suggested they may resume at some time in the future, but nobody knows why they suddenly ceased operations or when they might resume. I suppose an independent lab analysis now might be helpful for those who have some stock on hand, but Pacer's new management a few years ago was open about publishing a revised analysis of the current product, so all a new independent analysis would tell us is whether the new management was being honest. I'd like to give them the benefit of the doubt for now. As for the future utility of doing the lab test on current stock, the near-term future is none and the long-term future is uncertain. If Pacer comes back online, we can test whatever is their "new" stock. JMO

@PyewacketteAll of the oxides in Mason stains are regarded as safe if used in a stable glaze, no different than if said oxides were used as colorants in the typical amounts in a "normal" glaze. The reds and oranges contain cadmium and selenium which would be toxic by themselves, but Mason encapsulates them in zirconium so that they do not leach out of the stain particle. The advantage of using stains to color your glazes is the variety of colors that can be easily achieved without knowing oxide combinations and amounts to add to your base glaze. The disadvantage is cost. As with so many things, you can figure it out yourself the hard way, or you can buy your way out with the gentle application of some folding green.

@PyewacketteAll of the oxides in Mason stains are regarded as safe if used in a stable glaze, no different than if said oxides were used as colorants in the typical amounts in a "normal" glaze. The reds and oranges contain cadmium and selenium which would be toxic by themselves, but Mason encapsulates them in zirconium so that they do not leach out of the stain particle. The advantage of using stains to color your glazes is the variety of colors that can be easily achieved without knowing oxide combinations and amounts to add to your base glaze. The disadvantage is cost. As with so many things, you can figure it out yourself the hard way, or you can buy your way out with the gentle application of some folding green.

PM me if you want a printable copy of the Mason reference guide. ( I converted it to a pdf for my glaze chem class notebook)

@PyewacketteAll of the oxides in Mason stains are regarded as safe if used in a stable glaze, no different than if said oxides were used as colorants in the typical amounts in a "normal" glaze. The reds and oranges contain cadmium and selenium which would be toxic by themselves, but Mason encapsulates them in zirconium so that they do not leach out of the stain particle. The advantage of using stains to color your glazes is the variety of colors that can be easily achieved without knowing oxide combinations and amounts to add to your base glaze. The disadvantage is cost. As with so many things, you can figure it out yourself the hard way, or you can buy your way out with the gentle application of some folding green.

PM me if you want a printable copy of the Mason reference guide. ( I converted it to a pdf for my glaze chem class notebook)

@PyewacketteYup, you are doing it right already. When the wedged roll is sitting on its side lengthwise in front of you, standing it up clockwise is tilting it to the right. As for the stacking direction during the wire and stack, the only thing that matters IMO is keeping the layers of each half stacked parallel to the table. The concept is doubling the number of layers with each stack, and squishing them down to half their thickness from the previous stack. When showing the students, I keep a running count of the number of layers - 1 (the original block), 2, 4, 8, etc. Ten cuts and stacks yields 1,024 layers, each 1/1024 the thickness of the original block, intermixed so thoroughly you can't tell where any "lump" or dry or wet area from the original block is anymore. Ten more cuts and stacks puts you at over 1 million mixed layers. With the students, I usually start with one chunk of light clay and one of dark clay. Each cut I show them the colored striations of the layers, until somewhere around 15 cuts, it is totally uniform and there are no more stripes of color. As for orientation of rotation, I don't consciously worry. I have a very rhythmic lift of the block through the wire, and then rotate one wrist to slap that piece down upside down from its position when I pulled it up through the wire, and then immediately rotate the other wrist to slap that half down on top of the first piece. Twang whack whack. Twang whack whack.

Yes, I too mostly wire and stack, it is more efficient and more effective at redistributing the uneveness of any clay that either just came out of the bag or has been sitting around longer than an hour or two. I always finish with a quick few times around of ram's head wedging, mostly just to make the squarish chunk round - it throws better when it is round... The ram's head method is more or less symmetrical  left and right, as opposed to the spiral method. After ram's head wedging it, I turn it to the left and stand it on end, rounding the end a bit to roll out any air pockets. Then it is ready to throw on the clockwise wheel, with the spiral from the ram's head rotating in the proper direction to tighten the spiral. For you, Pye, you are already doing all of this up to the very last step. Instead of turning the ram's head to the left, you turn it to the right and the spiral will be oriented properly for you throwing on a clockwise wheel.

I'll let the professional electricians (you know who you are...) have the last word, but I have heard that these "ice cube" relays used in many Skutt kilns are subject to more heat stress than the brown ones used in most other kiln brands because these are crammed into too small of a space. Poor design of the control column. But what else can one do about it now?

@PyewacketteYup, you are doing it right already. When the wedged roll is sitting on its side lengthwise in front of you, standing it up clockwise is tilting it to the right. As for the stacking direction during the wire and stack, the only thing that matters IMO is keeping the layers of each half stacked parallel to the table. The concept is doubling the number of layers with each stack, and squishing them down to half their thickness from the previous stack. When showing the students, I keep a running count of the number of layers - 1 (the original block), 2, 4, 8, etc. Ten cuts and stacks yields 1,024 layers, each 1/1024 the thickness of the original block, intermixed so thoroughly you can't tell where any "lump" or dry or wet area from the original block is anymore. Ten more cuts and stacks puts you at over 1 million mixed layers. With the students, I usually start with one chunk of light clay and one of dark clay. Each cut I show them the colored striations of the layers, until somewhere around 15 cuts, it is totally uniform and there are no more stripes of color. As for orientation of rotation, I don't consciously worry. I have a very rhythmic lift of the block through the wire, and then rotate one wrist to slap that piece down upside down from its position when I pulled it up through the wire, and then immediately rotate the other wrist to slap that half down on top of the first piece. Twang whack whack. Twang whack whack.

Yes, I too mostly wire and stack, it is more efficient and more effective at redistributing the uneveness of any clay that either just came out of the bag or has been sitting around longer than an hour or two. I always finish with a quick few times around of ram's head wedging, mostly just to make the squarish chunk round - it throws better when it is round... The ram's head method is more or less symmetrical  left and right, as opposed to the spiral method. After ram's head wedging it, I turn it to the left and stand it on end, rounding the end a bit to roll out any air pockets. Then it is ready to throw on the clockwise wheel, with the spiral from the ram's head rotating in the proper direction to tighten the spiral. For you, Pye, you are already doing all of this up to the very last step. Instead of turning the ram's head to the left, you turn it to the right and the spiral will be oriented properly for you throwing on a clockwise wheel.

Yes, I too mostly wire and stack, it is more efficient and more effective at redistributing the uneveness of any clay that either just came out of the bag or has been sitting around longer than an hour or two. I always finish with a quick few times around of ram's head wedging, mostly just to make the squarish chunk round - it throws better when it is round... The ram's head method is more or less symmetrical  left and right, as opposed to the spiral method. After ram's head wedging it, I turn it to the left and stand it on end, rounding the end a bit to roll out any air pockets. Then it is ready to throw on the clockwise wheel, with the spiral from the ram's head rotating in the proper direction to tighten the spiral. For you, Pye, you are already doing all of this up to the very last step. Instead of turning the ram's head to the left, you turn it to the right and the spiral will be oriented properly for you throwing on a clockwise wheel.

@Bill KielbYup, and it gets worse. The 120F rate is embedded somewhere in all the Bartlett cone fire profiles with 108F only in a few slow bisque profiles. At least the cone-fire method has the adaptive algorithm to fall back on for an appropriate final temperature. Then we have the all-famous Skutt pinhole solution of a slow cool manual ramp-hold program circulating all over the interwebs that specifies the 120F rate to the top temp. And to make it worse yet, Skutt has removed the slow cool checkbox from their version of the Bartlett touchscreen. Their earlier 12-key Kiln Master had the standard Bartlett option to append a stock slow cool schedule onto a cone-fire, but now with their touchscreen, one must construct a manual ramp-hold schedule with whatever slow cool you want at the end. Is it better to give the user a quick all purpose slow cool checkbox on the cone-fire profile that has the adaptive function, or a fully user-customized slow cool preceded by a recommended 120F ramp to a specific temperature that will likely fail? Ackkkk...

Yes, the Orton table shows 108F/hour for the medium speed. Bartlett programs the cone-fire profiles at 120F/hr. That's why I caveated my comment with "depending on who you ask..." I have no clue why Bartlett is using a different rate, but my kilns seem to bend the cones just right at 120F/hr. And yes, I know they are going at 120F/hr - I have Genesis controllers and I download the log files to keep track of exactly what the the kiln is doing.

The reason I asked for your firing schedule is I suspect a technical nuance is at play here. Cones deal in heatwork - time and temperature. Nothing new with that idea. If the ramp rate in the final 2 hours is aggressive (relative to the Orton table, which depending on who you ask, what book you read, or what kiln controller you have, medium speed to cone 6 is 120F/hr to 2232F), the cone bends at a higher final temperature, and vice versa, a slower ramp will bend the cone at a lower temperature. Nothing new with that idea either. Your ramp 5 is set for 200F/hr to 2200F, which is pretty aggressive. Putting that into the Orton cone calculation spreadsheet, that would give you a cone 5.5, and even the 20 minute hold doesn't quite get to 6. However, the nuance that isn't always seen is that as the elements wear with usage, the actual ramp rate attained by the worn elements falters (and in the most extreme case, simply can't heat the kiln in the final segment and the controller errors out). While the cone-fire programs in the Bartlett and Orton controllers have an adaptive feature that monitors the actual final ramp rate and adjusts the target temperature to produce a good cone bend, the custom ramp hold programs do not have that capability. In ramp hold, the controller will keep chugging until the programmed temperature is reached regardless of how long that might take (unless it determines the rate is futile and it errors out). As the elements wear, the final ramp rate slows down and the cone should bend at a lower temperature, but the controller keeps going until the programmed temperature, and now the cone is overfired. Going back to the Orton spreadsheet, a ramp of 100F/hr to 2200 with a 20 minute hold should give you a cone 7, which it did. So, my suspicion is that your elements are wearing out, the programmed 200F/hr final ramp rate is bovine droppings, it's actually only making 100F/hr, and from here, it will get worse. Check the resistance of the elements and be ready to replace them as they drop too far out of spec. In the short term, drop you final temperature to 2185F and that should give you a nice cone 6 when the kiln is chugging along at the best it can do.

The reason I asked for your firing schedule is I suspect a technical nuance is at play here. Cones deal in heatwork - time and temperature. Nothing new with that idea. If the ramp rate in the final 2 hours is aggressive (relative to the Orton table, which depending on who you ask, what book you read, or what kiln controller you have, medium speed to cone 6 is 120F/hr to 2232F), the cone bends at a higher final temperature, and vice versa, a slower ramp will bend the cone at a lower temperature. Nothing new with that idea either. Your ramp 5 is set for 200F/hr to 2200F, which is pretty aggressive. Putting that into the Orton cone calculation spreadsheet, that would give you a cone 5.5, and even the 20 minute hold doesn't quite get to 6. However, the nuance that isn't always seen is that as the elements wear with usage, the actual ramp rate attained by the worn elements falters (and in the most extreme case, simply can't heat the kiln in the final segment and the controller errors out). While the cone-fire programs in the Bartlett and Orton controllers have an adaptive feature that monitors the actual final ramp rate and adjusts the target temperature to produce a good cone bend, the custom ramp hold programs do not have that capability. In ramp hold, the controller will keep chugging until the programmed temperature is reached regardless of how long that might take (unless it determines the rate is futile and it errors out). As the elements wear, the final ramp rate slows down and the cone should bend at a lower temperature, but the controller keeps going until the programmed temperature, and now the cone is overfired. Going back to the Orton spreadsheet, a ramp of 100F/hr to 2200 with a 20 minute hold should give you a cone 7, which it did. So, my suspicion is that your elements are wearing out, the programmed 200F/hr final ramp rate is bovine droppings, it's actually only making 100F/hr, and from here, it will get worse. Check the resistance of the elements and be ready to replace them as they drop too far out of spec. In the short term, drop you final temperature to 2185F and that should give you a nice cone 6 when the kiln is chugging along at the best it can do.

The reason I asked for your firing schedule is I suspect a technical nuance is at play here. Cones deal in heatwork - time and temperature. Nothing new with that idea. If the ramp rate in the final 2 hours is aggressive (relative to the Orton table, which depending on who you ask, what book you read, or what kiln controller you have, medium speed to cone 6 is 120F/hr to 2232F), the cone bends at a higher final temperature, and vice versa, a slower ramp will bend the cone at a lower temperature. Nothing new with that idea either. Your ramp 5 is set for 200F/hr to 2200F, which is pretty aggressive. Putting that into the Orton cone calculation spreadsheet, that would give you a cone 5.5, and even the 20 minute hold doesn't quite get to 6. However, the nuance that isn't always seen is that as the elements wear with usage, the actual ramp rate attained by the worn elements falters (and in the most extreme case, simply can't heat the kiln in the final segment and the controller errors out). While the cone-fire programs in the Bartlett and Orton controllers have an adaptive feature that monitors the actual final ramp rate and adjusts the target temperature to produce a good cone bend, the custom ramp hold programs do not have that capability. In ramp hold, the controller will keep chugging until the programmed temperature is reached regardless of how long that might take (unless it determines the rate is futile and it errors out). As the elements wear, the final ramp rate slows down and the cone should bend at a lower temperature, but the controller keeps going until the programmed temperature, and now the cone is overfired. Going back to the Orton spreadsheet, a ramp of 100F/hr to 2200 with a 20 minute hold should give you a cone 7, which it did. So, my suspicion is that your elements are wearing out, the programmed 200F/hr final ramp rate is bovine droppings, it's actually only making 100F/hr, and from here, it will get worse. Check the resistance of the elements and be ready to replace them as they drop too far out of spec. In the short term, drop you final temperature to 2185F and that should give you a nice cone 6 when the kiln is chugging along at the best it can do.