Dick White

Measuring the resistance of the elements is the most accurate way to determine if they are sufficiently worn that the kiln will have trouble heating, and thus the elements should be replaced. However, if one takes a close look at Ohms Law that mathematically relates volts, amps, resistance, and watts, amperage is an inverse proxy for resistance. Skutt kilns manufactured after 2006 all contain a current sensor that can measure the amperage being pulled by each section (some from before this date might have one too). This amperage measurement is built into the controller diagnostics and can be retrieved without opening the control column. If you do not have a copy of the user manual, you can download one here - https://skutt.com/skutt-resources/manuals/kilnmaster-manuals/. The original specification for the amperage of each section of a 1018 is 20 amps (both sections are the same). If the amperage readings are 18 or below, the elements are worn.

The report at the time from Laguna was that they picked up 3,000 tons of the stuff from the mineyard. That's a, well, I shouldn't say the word, but it is a lot. My guess is greed, but what do I know?

I may be remembering it backwards.

This discussion of a spod substitute blend is interesting in another way. I personally and the studios I work with have enough spod on hand to meet our needs for quite awhile, if only because we don't use much of it. I even have some of the old Foote, as well as the newer Gwalia. What strikes me now is how reminiscent this is of the time the Gerstley Borate mine closed. It didn't take long for a number of substitute blends to move into that vacant space - Laguna Borate, Gillespie Borate, CadyCal, Mexican blends, etc. Is that the future of spod - a dozen different blended substitutes to figure out? And what's with Gerstley? Laguna pulled 3,000 tons of the unprocessed ore out of the mine yard and brought it back to market. Now it costs as much as frit. Does that mean Laguna is running out and can charge a premium for what's left?

As Neil notes, the change from 2.5" to 3" bricks matters - sometimes. My community studio has a pair of 16-year old 1227s, and they are 3" brick. Measure yours to be sure. If I remember correctly, it was my observation when the changeover became standard, L&L kept the exterior dimensions the same which caused the interior to be smaller (and thus all the sheet metal did not change, but older shelves were too big to fit in the smaller interior), while Skutt kept the interior dimension the same which caused the exterior (and related sheet metal) to be larger. And yes, nearly all Skutts have two different elements. The top and bottom ones are hotter and the 4 middle ones are a bit cooler. I am not in the studio now either, so I can't look at my notes of Skutt part numbers, but the online sellers I've dealt with have all the options clearly laid out - you have to specifically choose 208V 3-phase during the ordering process, and don't get confused with the 1227PK model. Some have you order 2 top/bottom elements and 4 middle elements, others just ask the kiln specs and they put together 6 of the right kinds. Also consider Euclids.com - good prices and good service. The differences between the Euclids product and the Skutt product are: The Skutt elements are manufactured with little bends in the elements that match up with the corners of the kiln, and each element package will include 2 new ceramic insulators, 2 crimp connectors to connect the power wires to the element tails, and a packet of pins to hold the element in the groove in the brick. Euclids' elements do not have the little kink at each corner (but I didn't find that a problem), they do not include new ceramic insulators (but for all the years I used the Skutt elements, I reused the original insulators unless one fell on the floor and broke, now I have a whole box of them that I don't know what to do with), they do not include new crimp connectors (but I prefer the bolt connectors that Euclids sells as they are easier to use (you don't need an industrial crimper and strong hands to get a tight connection) and you don't loose a half inch of the wiring every time you cut the old crimps off), and they send a 6 ft. roll of high temperature wire to cut your own pins.

There are several issues in play here. First, about cone numbers - if you download a cone chart from this link https://www.ortonceramic.com/files/2676/File/Orton-Cone-Chart-F-022-14.pdf you will see the temperature/rates for every cone. Note that there is no cone 0, and cone numbers from 01 and up are actually running backwards, the temperatures getting colder as the number gets higher; cone numbers without a O in front of the number run as you would expect, the temperatures increase as the number gets higher. Thus, your array of cones 04, 5, and 6 do not relate to each other. There is 200+℉ difference between 04 and 5, which is why the 5 and 6 cones are unmoved when fired to 04. Cones above 3 are different colors in the box so you can easily tell them apart when loading the kiln, but the dye burns out during the firing, leaving them white. Second, about the accuracy of programmable kilns - they are not accurate out of the box. More often than not, they tend to fire hotter than the nominal temperature shown on the screen. The reported maximum temperature will correlate correctly to the Orton cone table linked above, meaning that the final temperature attained at slow speed will be lower than the temperature reported for medium speed, and higher yet for fast speed. That's just the way cones work - the bending process takes time as well as temperature to penetrate to the center of the cone (and the center of a ceramic piece). But back to the kiln accuracy - if the kiln is firing hotter or cooler than the cone bend, you can calibrate the controller to, in effect, fool it to add or subtract a certain number of degrees to what the thermocouple seems to be reporting, and thus adjust the actual results so that cone 5 (let's say) on the screen properly bends cone 5 inside the kiln. If you have never played with the controller adjustments, you should call Skutt and ask one of the technical reps to walk you through the process.

Put a single layer of Saran Wrap or similar thin plastic film over the silver bowl to protect it from possible chemical reactions with something in the clay. It is probable that nothing untoward would happen with the clay in the bowl, but don't take the chance on the unknown.

Well, actually, the elements in those wiring diagrams are in series. There are 4 separate elements total, 2 in each of the sections. To measure the resistance of each section, apply the multimeter probes at the power inputs to the elements. The resistance will be the sum of the two individual elements. For example, in the B18 diagram, each section has two elements of 10.2 ohms each, which should measure as 20.4 ohms across the power leads. Thus using an Ohms Law calculator, that section running at 240V will draw 11.7 amps. Doubling that for both the top and bottom sections yields 23 amps total, which is slightly more than the stated 22 amps, but close enough to allow for some slippage and wear. Continuing the example for the 23H model, each section has a 7.8 ohm and 6.6 ohm element in series, for a measured total of 14.4 ohms across the power leads to the elements of that section. At the specified 208V, each section is drawing 14.4 amps, which doubled for both sections of the kiln yields total amperage of 28.8 amps, which rounds to the specified 29 amps. You correctly note that some kilns have elements with different resistances. The B23 drawing you found is an example of that. In the top section, the element closest to the top is 7.8 ohms and the one in the middle is 6.6 ohms. The bottom section is the reverse, with the 7.8 ohm element closest to the base and the 6.6 ohm one in the middle. You say the Cress rep told you the top and bottom elements are 9.2 ohms. If we assume that your B23 is also rated as 29 amps total but at 240V (confirm that on the electrical rating plate on your kiln, I am just guessing here), then the amperage per each top and bottom section will be ~14.5 amps, which calculates to a resistance of ~16.5 ohms total for the two elements in series in the section. If one is supposed to be 9.2 ohms, the other must be 7.3 ohms. .

A completely off the wall idea - you are using a custom ramp-hold program. The controller memory can hold several custom ramp-hold programs. What happens if you program the same schedule into a different user number? Maybe there is a bad bit on the memory chip that is causing havoc? But using a different spot in the memory chip, the error will not occur? Or what happens when you do a plain cone-fire to cone 6 at medium speed? Does that drive the kiln past this 1975+/- error point? Just some more crazy ideas for a crazy issue that doesn't make logical sense...

It has be be full to the brim and under maximum vacuum before it will pug out. During the mix cycle, some will inevitable squeeze back into the vacuum pump and shaft box, you just have to scoop it out after you've turned the machine off and put the scraps back in the mixing chamber for the next batch. The machine also needs to be full for the mix cycle, otherwise the clay just accumulates on the mixing arms and spins. The "T" bars on the ends of the arms are angled to push the clay from one end of the machine to the other for mixing and pugging, but if there isn't enough clay in the chamber to fill out to where the angled T bars are, nothing will happen.

As noted above, potash spar (Custer) and soda spar (Minspar) have opposite balances of potassium and sodium. As Min notes, one can spike up the Custer with some nepheline syenite to boost the sodium content to equal the Minspar or use the neph sye to get all the required sodium (together with some other adjustments), but there is no good potassium source to spike the Minspar to equal the Custer.

Some feldspar history... G200 was a potash feldspar mined in Monticello, Georgia, but the ore was higher in potassium than other comparable potash feldspars, such as Custer. To resolve this difference, they blended it 70:30 with a soda feldspar brought in from a mine in Spruce Pine, North Carolina. About 15 years ago, the bean counters decided that trucking soda feldspar 300 miles to just to mix it with another feldspar was not economical, so they stopped that. The plain potash feldspar from the Monticello mine was relabeled as G200HP (for High Potassium) and the ceramic industry was advised to mix their own if we wanted to replicate the old G200. Some of us did, some of us bought a product blended by Lauguna and marketed as Old Blend, and others of us moved on to other brands of potash feldspar. About 10 years ago, the Monticello mine was exhausted, and G200HP is no more. The Imerys Corporation (which now owned the mine and product) found a potash feldspar similar to the old blended product (and other potash feldspars) in Spain and began importing it as G200EU. So, to answer your specific question - no, you can't buy G200HP anymore (but I know someone who has some). There is nothing else like it on the market that has that high level of potassium. I don't know if you can trust the label of what you just got as actually the old blended G200 that has not been widely available for a long time or maybe is the Spanish G200EU. Because of these nuances, using another brand of feldspar with your remaining G200HP or in place of it is likely to change the way your G200HP recipes turn out. Or you can take a deep dive into some glaze chem software and sort it out from there.

The dials that go from 0-100 provide infinitely variable power to the elements, much like the knobs on an electric stove. Low numbers yield low heat, high numbers produce high heat. Start with the dials set to 1 for 2 hours, then turn it up to 50 for 2 hours, and finally 100 until the witness cone(s) bend.

ok, popping back in now with a clearer "picture" in my head. I believe the early RK Shimpos used a single speed reversible AC motor, with the variable speed of the wheel head achieved through moving the conical rubber head on the motor shaft back and forth across the rubber edge of a disk on the lower portion of the wheel head shaft. The newer Whisper models use an electronically controlled DC motor. The "crossover" switch from The Ceramic Shop noted in PeterH's comment is for the Whisper model, and so would not be a replacement for the switch on an original RK model. However, looking at the last page of the wiring diagram also noted in PeterH's comment, there appear to be three different switches that might have been used - the SRH632-2 already discussed, an AK-AB-33P4, and a common DPST toggle switch. The first two switch types appear to be some sort of 3-position rotary switch that internally swaps the leads to the motor to reverse it, depending on which direction the switch is turned. The toggle switch is a plain on-off switch, for which reversing the motor direction involves going under the machine to reverse a plug in the line from the toggle switch to the motor. It would appear from the research already done, the 632 rotary switch is obsolete, no longer available anywhere. A quick Giggle of the AK-AB switch also comes up blank. But, if you are facile with wiring, the common toggle switch could be a way out, albeit the motor would no longer be reversible at the switch. But maybe for your purposes, you only run it in one direction so reversing isn't important?

Yes, no, maybe. We have no clue what colorants or what amounts of said colorants are in commercial underglazes. As for Mason stains (i.e., Mason brand), they do publish a reference document showing what colorants are in each stain number, but not amounts. Of the 5 black stains, 6600 and 6612 are listed as compatible with either zinc-free or zinc-contain glaze. The others, 6650, 6657, and 6666, specifically state zinc-free glaze needed. The issue is that zinc and chrome do not play well together. About 75% of the Mason stains have some chrome in the mix of colorants, so a zinc-containing glaze will alter the intended color of the stain. Hence, zinc-free being the go-to recommendation, especially for underglazes for which there is no public data.

NM

Nice job, been there done that too. Some years ago I acquired a little Paragon 1193 of about the same size, and also 120V, 19 amps. I thought it would be a nice test kiln. Not so, the elements kept wearing too fast at cone 6, despite it nominally being a cone 10-capable kiln. It had a 3-button Sentry controller. So, I did the math, changed the plug to a 20 amp 240 plug, swapped in a double breaker, but didn't need to change the wiring through the wall as it was already 12 ga. Bought a pair a generic 12 amp elements from Kreuger, wired them in series, and swapped out the Sentry controller for a Genesis Mini. Also sprang for an S thermocouple. 30% more power and 100% more accuracy. No space for the SSR stuff, so keeping the standard relay.

So, what we are saying here is that the weak point in the circuit is the breaker which can only handle 80% rated capacity if fully loaded for more than 3 hours. Thus, a 60 amp breaker for a 48 amp continuous load. The wiring in the rest of the circuit is all 6 ga (or better) to match the 60 amp breaker, including the kiln power cord, even though only 48 amps will pass. The only exception is the inch and a half or so of the prongs of the 6-50 plug and receptacle. Are they truly limited in their capacity to pass no more than 50 nominal amps, or is the plug and receptacle more about the NEMA configuration to prevent end-user mix and match stupidity?

We'd rather keep you in the group to talk about your pottery than see you living in a motel fighting with the insurance company after a fire.

It is true that 48 amp kilns are built with 50 amp plugs/receptacles on 60 amp circuits. So, yes, a kiln drawing less than 30 amps could use a 30 amp plug on a 40 amp circuit. But this kiln is likely pulling more than 30 amps (though we don't actually know, just doing the math from factory spec sheets), so the 30 amp plug is insufficient.

Still assuming that the elements are the ones specified for the original configuration, 2 things are possible: 1) The elements are sufficiently worn now that they are pulling less than the specified amperage, and that would get it slightly below the 30 amp breaker. But when the elements are completely worn and replaced, it would be above the breaker size. 2) Breakers are designed to carry only 80% of the rated load for long periods of time, hence the 125% rule for continuous loads of 3 hours or more. The 30 amp breaker likely did not trip because it wasn't overloaded for long enough, but it probably would have in the middle of a firing.

And didn't have a fire? Or at least toasted wires?

There are a number of inconsistencies here. The now-2-section kiln, if still containing the proper elements from when it was a 3-section kiln (which we don't know), would be pulling 31 amps (which is insufficient for the volume of the kiln and will have unbalanced heating, but that's not our problem; it's only our problem when our tax dollars are spent on a fire department call...). Under the 125% rule (which the electrician may or may not be aware of, some are, some aren't until pointed to that page in the code book), that would require a circuit of 38 amps, or rounding up to the next available breaker size, 40, which the picture shows was used and is correct. The plug and receptacle shown in the pictures is a standard 30 amp set. The power cord shown in the picture appears to be the original cord but with the original 50 amp plug cut off and replaced by a 30 amp dryer plug from the hardware store. That alone is insufficient for the kiln (and I can't imagine how the previous owner ran the whole kiln on that...). In the N. American electrical inventory, there is a 40 amp breaker, but there is no standard 40 amp plug and receptacle; it skips from 30 to 50 amps. Thus, the plug needs to be a 50 amp (6-50) set while the breaker and wiring would be 40 amp material (including the black cable coming in from the left that goes back to the main panel, which in N. American standard cable colors is 8 ga., suitable for 40 amps) . Let's just assume the electrician also properly used 40 amp wire inside the metal flex cable in that installation, but set an insufficient 30 amp receptacle to avoid having to repair the existing power cord's currently insufficient plug? Just too many unknowns.

Several concerns about the current state of affairs - you took out the bottom section, which changes the amperage draw from 48 amps to 31 amps, assuming the elements are the correct ones for a 240V 1027 kiln. That requires a 40 amp circuit, including the associated wiring. You said you were using a dryer circuit, which is typically a 30 amp circuit. You say the electrician changed the circuit breaker. Changed it to what amperage? If the sparky put the required 40 amp breaker on an existing 30 amp circuit, you need a new sparky and hope your homeowner's insurance is paid up. Regarding the kiln itself, the design of Skutt kilns places hotter elements in the top and bottom rows to compensate for heat losses through the lid and base. The middle 4 rows of elements are cooler because less heat is need in the middle compared to the top and bottom. By removing the bottom section, you have eliminated that one element at the bottom that needs to be hotter. It may have somwhat unbalanced heating now. Furthermore, though it is now the size of a 1018 kiln, kilns are designed with optimal ratios of heat to kiln surface area. The standard 1018 kiln needs 39 amps to perform up to maximum expectations. Yours now has only 31 amps. Thus, you will probably be limited to cone 6 at best.

Firing to 1240 and holding for 30 minutes is probably going to be same amount of heatwork as going 10 more to 1250 and shutting down.