Wiseman Ceramics

Disclaimer/Warning:
Automated kilns weren’t meant to be left completely unattended. I fire to a witness cone viewed through a spy hole, so I am there every time it hits peak. Others rely completely on the controller. If this is the case, you can try to Write your own Cone Fire program in order to smooth out some of the variables.

_________________________________

Many are finding inconsistencies in their glaze results from one firing to the next. The variables are vast, but I’m going to focus on three reasons attributing to inconsistencies. The first is that the kiln elements decline with use. The second is that kiln loads vary in weight and how that weight is distributed from one firing to the next. The third is due to heavily insulated kilns that hold too much heatwork following the top end of the firing.

The first thing to understand, is that a cone measures heatwork, not just a given temperature. Heatwork is a measure of heat + time. Time refers to how long it takes to get to peak temperature, as well as any hold maintained once that peak is achieved.
If the kiln is in good working order, it should have no problem achieving the desired rate of rise and peak temperature. But, if your elements aren’t new, or if the kiln is packed heavy, it could take longer than you programmed to get to the intended temperature. If your kiln achieves the programmed temperature over a longer period of time, over-firing will most likely result.

Example: ^10 (true 90 degree bend) equals 2342°F, only if the kiln can maintain a 108/hr rise during the last 150-200° prior to peak. If it takes longer, then the temperature you need to reach will be less. Again, both heat and time must be factored in.

To continue, I’ll need to use my L&L Dynatrol (Bartlett V6-CF) controller as reference.
If you wish to write your own cone fire, program a Vary Fire schedule the same way as usual, except that when it asks for the peak temperature, push the Other button. Keep pushing Other until you see Cone displayed. Type in the cone number you want to achieve (e.g., “10″). The controller will calculate the temperature to hit based upon your programmed rate of rise. Then, if your kiln lags during the firing, the controller will recalculate the temperature based upon the actual rate of rise.

For heavily insulated kilns yielding an over-fired cone, I’ve found that inputing a cone offset helps. Doing this can aid in compensating for the residual heatwork responsible for bending the cone beyond the point you want. Before you do this, you’ll need to monitor a firing to see how much to offset. Also, keep in mind that if your kiln is heavily packed, the ware will hold heat, accounting for inconsistencies as well.

Inputing a Cone Offset: Before you begin inputing a program, hit the Other key until you see CnoS displayed, then hit Enter. Typing “90″ before the desired offset temperature will yield a lower actual temperature, decreasing the amount of heat work achieved. Again, the idea here is that the residual heatwork will bend the cone further (hopefully closer to perfection).

You can only offset the cone measurement by 50°F, but if you need to do more than this, contact the manufacturer, as it eludes to a larger problem. Offsetting in this way will only affect the cone you select. It will not affect your thermocouple readings during other Vary Fire or Cone Fire programs. Speaking of thermocouples, none of what I’ve said here will help, unless your thermocouples are reading accurately. See the post on Studio Kiln Thermocouple Calibrations for more on this.
After reading this, you may begin to understand why I always fire by a visual cone in achieving the correct level of final heatwork. Computers haven’t completely replaced humans yet for a reason! I also prefer a kiln that allows for a fast descent, largely eliminating the effects of residual heatwork.

In February 2008, I was able to get the technician from the energy company to install another inline meter, this time on the JD18-JH electric kiln (for referencing the last meter, see the post: Electric Kiln Actual Energy Consumption).
The meter was set up to record ONLY the electrical consumption of the kiln.

After my 30th firing to ^11-12 and many lower temperature firings, the elements on the kiln look great, and ohm readings from the elements are pretty much the same as when the kiln arrived.

Meter Start Point:

When the meter was installed, it read: 400Kw/h. This will be our “zero point”.

_____________________________

1st Firing: This image was taken during a crystalline firing, immediately after seeing ^11 achieve a 45° bend.

Reading 1a: 434 - 400 = 34 kw/h used.
Cost (at 9¢ a kw/h): $3.06

… following the ^10.5 peak, there was the crystal soak phase of the firing. This involved ramping up/down and holding between 1900-2000°F (total hold times ≈ 4 hrs).

Reading 1b : 456 - 434 = 22kw/h used for heat-soak.
Cost: $1.98

Reading 1c: 456 - 400 = 56kw/h used for the entire firing.
Cost: $5.04

Summary: The total cost of a ^10.5 crystalline firing, including the 4hr. heat-soak costs about $5.00, and the $2.00 it cost to grow the crystals pretty much does away with the notion that crystalline firings are much more expensive than corresponding firings to the same peak.

This firing was done in the JD18-JH. One of it’s design characteristics is to cool out of the top heatwork zone before the perfect cone bend (and the glaze!) can be altered by residual heatwork. One of the arguments against this design was that it would either have trouble hitting the temp’s I wanted, or it would require so much power that firing would be expensive… obviously, neither is the case.

Following the crystal growing holds (heat-soak), the drop through quartz inversion and below was slow and smooth. When I unloaded the kiln, my witness cones looked nearly identical to what they did when I stopped the kiln’s peak temperature hold and began the descent.

Of course, if I’m going to fire the kiln, I may as well put something in it, yeah? …

__________________________________________

Second Firing: achieved ^020 @90° bend:

Reading 2: 463 - 456 = 7 kw/h used.
Cost: 63¢

__________________________________________

3rd Firing: Achieved ^05 @90° bend:

Reading 3: 482 - 463 = 19kw/h used.
Cost: $1.71

_________________________________________

4th Firing: Achieved (another) ^020 @90° bend:

Reading 4: 489 - 482 = 7 kw/h used (Compare to 2nd firing: Man, I like seeing repeated accuracy).
Cost: 63¢
__________________________________________

Related Links:

Electrical Consumption of a JD230HD (@7cu.ft.)

Main Kiln Energy Consumption Page

Has anyone seen the commercial concerning a popular allergy medication where a sculptor (wearing eye protection -but no dust mask) is creating from a block of stone with what appears to be an angle grinder? Airborne particles visually fill his immediate area as he works –then the scene cuts, and he says he uses _______ for all his allergy issues…
The next time I saw it, I noticed a cat sitting in the room with him. Were they honestly trying to insinuate that the cat dander is the real concern for this guy’s nasal, bronchial, and lung tissue irritation?

Silicosis is the result of silica (from clay, stone, glass, etc.) dust, which is toxic to the lining of the lungs. When silica particles contact lung tissue, a strong inflammatory reaction occurs. Over time, this inflammation causes the lungs to become irreversibly damaged. This falls under the term fibrosis, a condition which is both debilitating and deadly.

From the searching I’ve done, the “sculptor” is portrayed by actor Jon Eric Preston. On the medicine’s official website, all the actors are “representative of the real symptoms that allergy sufferers experience and the clear relief that ________ delivers in many real life situations”.

Ok -well, in real life Preston is skilled at many things from snake handling to firearms. Perhaps next they’ll ask him to do an adhesive bandage commercial where he acts out the fine art of Russian Roulette…

Related links:

U.S. Department of Labor: Facts on Silicosis

Silicosis and Screening by Edouard Bastarache

There are many good kilns available, but choosing one to suit your needs can be difficult. Take note that simply because a kiln boasts a “Rated to Cone 10″, “Energy Efficient” or “Heavy Insulation” label, it does not necessarily mean it is the best choice.  As a matter of fact, that last one can even cause you a good deal of grief.

I believe a good analogy to use toward an electric kiln, is that of a boat.  This may seem like an odd comparison at first; however, consider that both require power to operate against resistance, and since neither has brakes, it is up to the user to compensate for the dissipating momentum. This “momentum”, in the case of a kiln, translates to residual heatwork.Firing a heavily insulated kiln then, is comparable to piloting a heavier and less agile boat –for even after a pyrometric cone achieves the desired bend, it can easily drop well past that perfect arch if your kiln releases heat too slowly.It is also important to realize that automated controllers don’t make this any easier to deal with. A controller can stop supplying power to the elements, but it cannot make a kiln cool any faster than it’s ability to release heat. The user still has to figure out how to compensate, and then program the controller accordingly.I believe the best way to get the kiln that is perfect for your firings is to either build it from scratch, or start with a commercially manufactured shell of the size needed. Whichever choice you go with, the options to consider adding should focus on the need for accuracy and account for the components that will wear out the fastest.The variables below are those that led to designing the kiln I fire.

Variable 1 - The ability to heat:The kiln should at least have the ability to climb all the way to it’s top-rated temperature at 270°F/hr –without lagging. To accomplish this, the kiln needs enough power. I would suggest erring on the side of an “overpowered” design, for if your kiln lacks the ability to ramp fast when new, it will surely be difficult to reproduce results after the elements and other components age even slightly.The correct match between that power and the heating elements must also be calculated. Whether you go with standard or heavier gauge wire, it will have to be factored into a good watt density. As each kiln is going to be different, this subject gets much more involved than this post allows for, so I suggest speaking to a qualified individual (contacts I’ve had good experience with include: L&L, Geil, Skutt, Euclid, Kanthal).APM’s are often said to be the best choice for high temperature work. The long holds (”heat soaks”) used to grow the crystals in a glaze cause “grain growth” in standard element wire, thus weakening the metal. The thought is that since APM’s possess a different structure developed through a sintering process, they aren’t as susceptible to the damage produced by long holds at high temps.Having said this, my kiln currently runs with longer lengths of 12 gauge Kanthal A1 elements. This wire has proven more resistant than thinner gauges to the effects of higher temperatures, as well as the chemical attack occurring from clay and glaze during the firing. These elements currently have over 60 ^11-12 crystalline firings on them, show no visible signs of degradation, and perform with the same efficiency as they did when they were new.-Also, A-1 wire is about 1/3 the price of APM. Beyond power and a good watt-density, the kiln will need adequate insulating properties to retain the heat. Notice that I chose the word “adequate”…

Variable 2 - The ability to cool:Heavily insulated kilns heat well, because they hold heat well. This fact is often used to qualify them as “efficient”. But such a kiln’s Achilles’ heel resides in the inability to release heat at higher temperatures. I do understand that this goes against the current industrial tendency to add more and more insulation, but I hold that the value in a kiln that allows for a rapid diminishing of heatwork after achieving the desired cone value is extremely underrated.In 2006, Diane Creber passed on to me a wonderful collection of literature on crystalline glazes, including some of David Snair’s notes & letters. This information, along with my own correspondence with Derek Clarkson and others, showed a common preference in using small, high-powered kilns capable of completing the first and second phase of the firing (the climb to peak & descent to the first hold) in a short time frame. This, in my mind is a truer example of “efficiency”. I have fired several types of clay and glaze in kilns of various sizes, and there’s nothing like relying on a kiln capable of completing the entire firing program as it is actually set by the user.Many of the more spectacular glazes I’ve worked with require a very accurate firing. With crystallines in particular, my goal is to heat the glaze well past its melting point, possibly maintain a hold to dissolve silica, zinc, and excessive nuclei, then quickly halt run-off by descending into the next ramp. As all of this must occur within a very small window of time, excessive residual heatwork is the last thing you want.Variable 3 - Structural Integrity at High Temperatures:It seems obvious to choose kiln parts that are designed for the temperature and type of firings intended. But this is something that is overlooked often enough.At it’s core, a kiln is simply a strategic stack of insulating firebrick. These bricks, cut to fit and usually wrapped in a metal skin, make up “the kiln shell”.K23 brick is the current standard for most hobby/studio kilns. If you are only going to ^6-^8, then it’s a suitable choice; however, both ^9 & ^10 (as high as 2381°F, depending on your rate of rise), occur at or beyond the recommended range of k23. The hotface, or the side of the brick exposed to the interior of the kiln, can shrink and crack if exposed to temperatures beyond the rating (e.g., k23≈2300°F). Keep in mind that this will occur even if you are only firing that hot occasionally, or if you are firing to a slightly lower temperature and holding there to achieve the equivalent level of heatwork.In designing my own kiln, I selected k25 brick, because I like the option of firing hot… often bending ^11-12.My firings show four important benefits with regard to K25:

• The k25 brick is less fragile than k23.

• The k25 brick performs extremely well from 2000°F to peak without deforming…

• …it then allows for fast cooling from the top temperature down to 2250°F.

• It still, however, releases heat slower through the middle to lower phases (1500-500°F), when dunting and crazing typically occur.

Variable 4 - Accuracy:Along the same line of using brick rated to your needs, consider the ill-advised use of Type-K thermocouples (rated only to ≈2200°F), which still come as standard equipment in many high-fire kiln models. The option of using protective sheaths on Type-K’s can create a lag in temperature readings. My suggestion is to always go with a thinly sheathed Type-S thermocouple for any firings above^6.Refer to the post on Studio Kiln Thermoucouple Calibrations.If you’re replacing a kiln of roughly the same size, go with your notes on how that kiln fired –both up and down. Did one section typically lag behind during the ascent and/or descent? Now would be the time to add insulation to that particular section, or to the floor or lid. Remember to start with the least amount you need however, and add more only where it’s necessary… otherwise, you’ll be right back in the same (big) boat, so to speak.Variable 5-Efficiency & Energy Consumption:An argument against building a kiln as described here, is that the result seems under-insulated, and to require more power.  It may therefore appearing inefficient by modern standards.What I am focusing on here, is a small to medium sized kiln meant for studio use, when reproducing accurate levels of heatwork is important. If your goal is to run several large kilns on a daily or weekly basis, and you are firing glazes with a wider heatwork tolerance, then the few dollars you save per firing is certainly a significant consideration.On that note, and to qualify my view toward energy efficiency, I refer you to the relevant post on the actual power consumption of an electric kiln.Related Links: New L&L JD18-JH

Thermocouple Calibrations

I’ve currently performed seventeen ^11-12 firings with my new kiln, and the elements look and read great, showing no signs of getting tired.
After my 15th firing, I did a test run by programming a 350deg/hr. rise to Cone 9. The kiln managed the programmed ramp to the calculated temperature –no problem.

*As a reference, with my older kiln using the standard run of holders, I was averaging 25-30 high-temperature firings, and noticed signs of element fatigue by my 15th firing. Keep in mind, that I’m doing some pretty harsh firings, so others may get better life.
But an extreme test is often the best test.

Back to L&L JD18-JH Electric Kiln

Ever wonder how much it really costs to fire your electric kiln?

Follow these links:

L&L JD230HD Kiln (@7cu.ft.)

L&L JD18-JH Kiln(@3cu.ft.)