Dick White
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Posts posted by Dick White
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In the UMF calculation, the underlying notion is that you are counting the number of mols of each of the usual ceramic oxides, and developing a ratio of the number of each in a sample. A mol is simply a chemist's unit of counting. One can have a dozen pencils (12) or a ream of paper (500 sheets). A mol is ~6 x10^23 atoms or molecules (6 bazzilion). After doing all the math on the molecular weights of all the various oxides in a recipe and then reducing the sum of the flux molecules to 1 mol, the number of mols of alumina, silica, boron (the most important of the non-flux oxides) in the recipe sample will also be calculated. For the 1 mol of flux molecules, you can have innumerable ratios of the individual flux oxides within that 1 mol. For example, you might have .35 mols of sodium and .55 mols of calcium and .10 mols of magnesium oxides equaling the 1 mol of total fluxes. Once the 1 mol of fluxes has been set, the number of mols of the other oxides is revealed. For a typical cone 6 glaze, the quantity of alumina oxide will often fall between .25 and .5 mols, the quantity of silica oxide will often fall between 2.5 and 5 mols, and the quantity of boron oxide might be around .15 mols. These ranges are not required amounts, but rather are generally accepted targets for a stable glaze. There might be other reasons you want a glaze that is outside these typical ranges, but knowing how the ratios relate to each other will allow you to adjust a glaze recipe by adding or subtracting particular materials that have the oxides that you are trying to adjust. For example, if you want your recipe to have more sodium oxide in the 1 mol of fluxes, adding whiting (pure calcium carbonate) will not help. But if there is whiting in the recipe, you can subtract some of that to cause the balance of sodium within the 1 mol of flux to go up.
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We have been using Advancers in the glaze kilns at the college for over 10 years. Costs were not an issue as we got grants. The main reason we liked them so much is they are nearly indestructible (if you treat them properly). With student glazing errors, drips pop off with a stiff putty knife and a few swipes with an old green grinding wheel held sideways cleaned up the rest. No more chiseling and grinding divots into the corderite shelves, no more kiln wash. When we bought new kilns at the community studio, I just told them to buy Advancers for the glaze kilns. Same problem with everybody trying to do the Amaco drippy layered look and causing puddles of glaze on the shelves. Maybe in your own private studio, you have better control over your glazing, and when you make a mistake, you learn from it (which the students and community users don't pay the price for their errors). In my personal studio, I do some crystalline glazes which, by definition, are runny. Sometimes the catcher pot breaks from the stress. Advancers to the rescue.
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Two similar elements connected in series will generate one/half the heat of one element alone. Two similar elements connected in parallel will generate twice the heat of one element alone.
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Often, that clicking sound indicates the bat is not securely fastened to the wheel head because the bat pins are not securely fastened, and both the pin and the bat are wobbling. I lot of potters I have observed believe it is sufficient to just stick a bat pin in the hole and it will solidly stay there. Until it begins to wobble in the hole with the varying pressure on it while centering. Others know that the pin will be loose in the hole and try to accommodate that by wrapping a bit of paper around the pin before shoving it into the hole. Until the paper gets wet and the pin begins to wobble in the hole. The solution is wing nuts to tighten the bat pin to the wheel head from underneath. Wing nuts take some facile finger work to get them started on the pin, and more finger/thumb strength to twist them tight. Sometimes they will work themselves loose and the clicking is the signal to stop and tighten them again.
As for the one oblong hole on the bottom of the bat, note that the oblong dimension is aligned with the radius (diameter) of the bat. That allows one to get the first pin set and still be able to move the bat crosswise to set the other pin. The movement is restricted to across the diameter of the bat, not tangentially around the circumference of the bat. Once set the bat should not move either crosswise (because the hole for the other pin exactly fits) or around the wheel (because the oval hole does not have any tolerance in that direction). Thus, the only possible movement is a loose pin not firmly tightened against the wheel head.
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The OP shows a location in the UK and price limits in pounds. The standard electric service there is 230V. In the US, standard residential electric service is 120/240V, where the normal household receptacle is 120V and other special purpose receptacles are 240V. Thus, in the US, there are a variety of kilns designed for either 120V or 240V service. I don't think there will be any 120V kilns in the UK, but I could be wrong.
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All the time now. Gerstley is gone and Gillespie is not a perfect match. 3134 requires a complete rewrite of the recipe. Custer is gone from the market, but I still have some. G200EU might be ok, haven’t tried it yet. Still have some old Amtal talc, but some Fabi is in my future. What’s next?
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At 800 degrees, the glaze particles have not begun to sinter, they are just a little toasty. Fix the kiln and refire.
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As others have already noted, neither zinc oxide nor chrome oxide used in reasonable amounts in a stable glaze are toxic. A different issue arises when both are used together in the same glaze - ugliness abounds. Chrome is supposed to be green when in a glaze that does not contain tin. A combination with tin in the right amounts creates a variety of pinks and reds. Zinc with chrome, however, turns assorted shades of brown, when copious amounts are used. It won't hurt you, but you probably don't want to look at it. Perhaps your glaze recipe doesn't have enough for the adverse color reactions.
- Pres, Beccap, Callie Beller Diesel and 2 others
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5
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The Sentry FTH error is similar to the Bartlett E1, in that both are in response to the controller detecting the temperature not rising as expected according to the program. The difference is that the Sentry continues to fire, albeit slowly, until the target temperature is finally reached, whereas the Bartlett error will terminate the firing.
- Hulk and Bill Kielb
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2
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Digitalfire has a materials analysis of it here:
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For Flux Sake is one of the offshoots from the inestimable Matt Katz, who in one of his webcasts long ago expressed an opinion that in addition to the usual list of pinhole suspects, poor application of the glaze was often a cause, particularly with brushed glazes. If the first coat of glaze had irregularities, those nooks and crannies could be covered by the next coat, leaving a tiny air pocket underneath. The problem is especially acute on textured surfaces. As the glaze melts during the firing, those little air pockets would rise to the surface and pop, leaving the pinhole. So, in Matt's opinion, pinholes could be from user error as well as decomposition of the glaze or outgassing from the body. Matt typically uses porcelain tiles for his testing, and bisques to 08 for consistent absorbency. A clean body such as porcelain does not need the higher bisque to burn out the organics and impurities.
- Bill Kielb and Hulk
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13 hours ago, neilestrick said:
Does it have a 'copy' function like the Genesis, where you can copy the Cone Fire schedule into a custom program?
Dunno, I don't have a Skutt Touchscreen, and the "user manual" is a help screen embedded in the controller. All I know is what I hear from others who are struggling with it.
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Sometimes even when the elements look good and turn red, they are worn. The only way to definitively determine the health of the element is measure its resistance with a meter. The L&L manual kilns have variable controls for each section. If the bottom is running cool (common), you can compensate for that by have the bottom dial on full high and the middle and top a bit below high. You'll have to experiment with that until you learn exactly how your kiln behaves.
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@Bill Kielb and @Potpotpotter The Skutt Touchscreen controller, while built by Bartlett to Skutt's specifications and similar in many ways to Bartlett's own Genesis, does not have the toggle to turn on the optional cooling segment as the final segment of a cone-fire (auto-fire) program. Such a capability was available in the Skutt KM series kilns using the controller logic adapted from the Bartlett native V6-CF controllers, Skutt removed that from their Touchscreen version of the Bartlett Genesis. With a Skutt Touchscreen controller, one now must build a custom ramp-hold program that mimics whatever cone-fire program on the way up and then add one or two more steps at the end of the program for a controlled cool.
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Many years ago, one of the students in the college class lost the bottom nut from the extruder die holder while cleaning it in the cleanup bucket in the sink. Irritating, but not the end of the world to have to go to the hardware store for a replacement nut. We periodically scoop the sludge from the cleanup bucket into the main recycle barrel, and when that barrel is full, I pug the recycle in to a proprietary mix that is so proprietary that even I don't know what I put in the pugged clay logs. Despite the unknown mix, it's usually nice enough to work with for class demos and experimental practice work. About a year and a half later, I was making a batch of Empty Bowls, and felt a lump in the wall of the cylinder. Thinking it to be an air bubble, I poked it with my needle tool, but it was a hard chunk. So I dug it out, and there was the long lost nut.
- vastglassylake, Pres and Rae Reich
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There is some conflicting information about the first firing floating around, both from different kiln manufacturers, for different purposes, and even within the same manufacturer's instructions. L&L's printed manual has long instructed owners of their new kiln to do an initial break-in firing of the empty kiln (but with the furniture) slow bisque to cone 5 (yes, five, not oh-five) with a 3 hour preheat for the dual purpose of seasoning the elements to develop a protective oxide coating and to set the cement used during manufacturing to hold the kiln bricks together. Their newest manual indicates these instructions are for both the Dynatrol and Genesis controllers.
Conventional wisdom by some other kiln manufacturers instruct owners of their new kilns to do the initial firing slow to 04. This is consistent with the recommendation from the manufacturer of the Kanthal elements for seasoning newly installed replacement elements, again to develop a protective oxide coating on the wire. Out on the interwebs, many commenters who own these other brands of kiln will adamantly (but incorrectly) assert that new owners of all brands of kilns should do the initial firing to 04.
And now we have this new video from L&L for programming the first firing on a Genesis controller that instructs a glaze firing to 04 with a 1 hour preheat. However, if one looks around on the L&L website, there is another video for programming the older Dynatrol controller for the first firing that is consistent with the printed instructions, i.e., slow bisque to 5. Is the basic kiln constructed differently for a Genesis vs. Dynatrol controller that it would need a different initial firing? I don't work there, so don't take my word for it, but the conflict seems fishy to me. With 3 instruction sources to choose from (the printed manual and 2 videos), I would go with the 2 that are consistent, i.e, the printed manual and the Dynatrol video. But maybe that's just because I am a recovering accountant...
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DigitalFire can tell you about the usage of most of those. https://digitalfire.com/material/list
- Piedmont Pottery and Hulk
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Ok, now download the firing log and feed that sweet thang into @jay_klay_studio's graphing program to visually see the tracks of the 3 sections. And if you really want to have some fun, add another 9999 drop all the way down to 100 after your regularly programmed cool to log how looooonnnggggg it takes for the last several hundred degrees. Several times over the years I've printed the extended graph of a few kilns as a teachable moment for the students of the virtue of patience, i.e., "Can I get my piece tomorrow?" "No, next Friday."
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Been rode hard and put up wet.
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For the brush hair, you can go to a full line fishing store and get squirrel tail and deer tail used to tie fishing fly lures.
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The reason most studios are picky about not allowing outside clay is because of the risks involved in the glaze firing. Earthenware bodies or glazes mistakenly put in a mid-fire glaze firing will create a terrible mess. "But the label on the box had a number 6 in the cone rating. Oh, the zero in front of the 6 was meaningful? How was I supposed to know that." (Yes, I have had that very conversation with students.) The other side of the issue is just about all bisque traditions are similar no matter the intention of the body in the final glaze firing. So, bisque firing a low-fire raku clay to cone 06-04 is no different than bisque firing a cone 5-6 clay to the same 06-04, or even a cone 10 clay bisqued to the same 06-04. My guess is if you respectfully talk with the studio management about your opportunity for the raku firing and ask them to bisque fire this non-standard body, hopefully they will understand there is no risk and accommodate your special request.
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@Bill Kielb alludes to an important aspect of a kiln vent - make up air. For whatever air is being exhausted, there must be an equal amount coming back into the room. The challenge for a kiln vent, is that make up air must come from a different direction from the exhaust. If the location of the make up air, such as another open window or door in the room, is too close to the exhaust vent, the stinky air will just be sucked right back in through that opening. The make up source needs to be around the corner from the exhaust so that the stinkies dissipate in a different direction and the make up air is clean.
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The Bartlett and Orton controllers have an algorithm (designed by Orton, licensed to Bartlett, so both have it) built into the cone-fire mode that senses actual heating rate (which may or may not be what was programmed) and adjusts the final temperature for the intended cone bend. As @Bill Kielb notes, the Orton tables focus on the last 100C/200F, and the published cone-fire firing schedules for Bartlett controllers all start the final segment at 250F below target temperature regardless of cone or rate. In my kilns which are all performing well, the Genesis logs show this happening as programmed; the final ramp at medium speed is a straight line at 120F per hour. What I do not know is, if the kiln were faltering in the final segment, does the controller average the achieved rate over the segment, or adjust incrementally as the segment progresses. In some of my diagnostic work with others' failing kilns, the rate of increase may be reasonable at the beginning of the final segment, but slows down significantly by the end of the segment (i.e., the graphed temperature is a curve, not a straight line) so how does it calculate the appropriate end point? What does this mean for your programming? I don't know, just throwing it out there that many potters think that if the controller finished without an error code, their kiln is in good shape, when it is not. The controller is working around the kiln failure. You'd like to mimic that, which is awesome.
Wood ash glaze conundrum
in Clay and Glaze Chemistry
Posted
To calcine clay (ball or kaolin), just put a big bisqued bowl of it in your next bisque firing. Unlike some other materials that might sinter if calcined to too high of a temperature, clay is refractory and can withstand bisque temperatures, so just use your next bisque firing for calcining it rather than using your propane for firing a single item.