Care and Feeding of your Paragon SC Kiln
Last year I had the opportunity to attend a kiln maintenance seminar at Paragon Industries. While much of the information presented was far beyond anything you or I will ever use, there were plenty of pearls that were very enlightening and useful for the home kiln user. Just knowing what is normal can ease a lot of apprehension about things that actually make no difference in the kiln operation. Hopefully this will save you a lot of unnecessary stress and worry.
To quote John Hohenshelt, President of Paragon Industries, "A kiln is a box that gets hot." Its needs are fairly simple. It requires a way to get hot (heat source), a way to contain the heat and a way to control the heat. For an SC ceramic fiber kiln that translates to electric elements which are embedded within an insulating ceramic fiber muffle and a computer controller.
These types of kilns are intended for home use and are wired for regular 120v household power. Ceramic fiber heats much more quickly than fire brick, making it much more economical to use. A typical metal clay firing costs just pennies. They are also available with a variety of door options, such as windows which facilitate enameling and glass fusing, and bead doors for lampworkers.
How difficult are they to use?
Operation of the controller is push-button simple. Basically, you are only controlling three things; how fast the kiln gets hot, what temperature it reaches, and how long it holds at that temperature before shutting off.
The first step of the program is called the "Ramp Speed" and refers to how fast the kiln gets hot. Full speed is approximately 1800 degrees per hour. For most applications you will want the kiln to get hot as fast as it can, but if your firing has inclusions such as ceramics or cork clay, you may need to slow it down a bit. Too fast a firing can cause ceramics to break and cork to burn off too quickly. You can slow the kiln down by reducing the ramp speed. For example, a rate of 1200 to 1500 degrees per hour is generally sufficient for ensuring the safety of firing metal clay with small ceramics elements or cork supports.
The second step of the program is the temperature at which you want to fire. Metal clay fires anywhere from 1110 to 1650 depending on the brand and formula of clay being used. Enamels fuse between 1400 and 1500. These are just a couple of examples of temperatures you might be using. You'll need to check what temperature to use for your specific application.
The third step is the hold time. How long do you want the kiln to continue firing once it reaches the desired temperature? For metal clay this will be anywhere from five minutes to two hours.
The door is loose! What do I do?
One of the most common misunderstandings is thinking the door should create a tight seal with the body of the kiln. Not true. While the kiln door does hold in heat, by design it does not create a tight seal. The insulating material of your kiln will expand as the kiln heats and contract as the kiln cools. The amount of this expansion will vary depending on how hot you are firing your kiln. This expanding material has to have somewhere to go, so the door is designed to have a certain amount of play to accommodate the changing conditions. If it were tight, as people often expect, the door would actually end up cracking or possibly even breaking when the insulation expands on heating. The result of all this is you may see the light of the heat around the door during firing. This is normal and should not be a cause for concern.
What about lost heat from the gap around the door?
The short answer is, this isn't a problem. Don't worry about it. The long answer is a bit more complex. Most of us are familiar with convection heat. Heat travels with the movement of air molecules, the hotter molecules moving up and the cooler down. This is a good enough explanation for things like stoves and hair dryers, but physics is a funny thing and the behavior of heat changes as temperatures get higher. You know that hot air rises, but did you also know that air expands as it is heated? That means as it heats, there is more and more room between the air molecules. By the time you get to about 1100 F there is so much room between the molecules that, in fact, there is virtually no air left in the kiln at all. So if there are no air molecules moving around to transfer the heat, what is causing the temperature in the kiln to continue to rise? What has happened is that we have moved from the world of convective heat to the world of "radiant" or "line of sight" heat. Air movement no longer plays any part. If I put my hand near that gap in the door, yes, I will feel heat; but it has no bearing on the firing going on inside the kiln. I am not "losing" any heat because my firing does not depend on air movement but rather on line-of-sight from the elements. When you open your kiln the temperature drops not because hot air is escaping your kiln, but rather cool air from the room is entering your kiln. As long as the pieces in your kiln are exposed to the element heat then they are firing properly.
The ceramic muffle in my kiln is cracked!
Your ceramic muffle may have had small cracks on arrival or it may develop them over time and use. Minor cracks in ceramic fiber are another area where people often worry needlessly. They do not affect the operation of the kiln. As the kiln heats and the fiber expands, these small cracks will tighten up in any case. Unless pieces are falling out, or the elements have become exposed, the cracks are merely cosmetic and do not affect the kiln operation at all. If it appears that pieces of the muffle may fall out or the elements become exposed, then you can contact your kiln manufacturer for a filler material that can be easily applied to repair these minor issues.
Remember, a kiln is a tool and will show normal wear over time. Just as your rusty old hammer continues to work just fine, as long as your kiln is firing normally, you should not let these minor cosmetic issues concern you.
There is black stuff on my kiln shelf and/or on the walls/roof of my kiln.
This is normally caused by burnout materials such as cork or wood clay, paper or other materials that are intended to burn up during firing. Usually these items burn out completely, but occasionally they may leave a residue. You should remove the vent plug from the top of your kiln when burning out materials. If you don't, you may end up with black marks around the door on the face of the kiln. This is cosmetic discoloration only and doesn't affect the kiln operation.
To remove black marks from the inside of the kiln, take everything but the shelf out of the kiln and fire it to 1600 for 30 minutes. At this point the ceramic fiber muffle and shelf should be white again. If it is not then your kiln may not be firing completely. If this happens you may need to contact your kiln manufacturer for additional help, but I will tell you now, that it's very rare and it is unlikely you will ever have this problem.
My kiln won't come on!
First, is it plugged in? If so, is there power coming from the outlet? Try plugging in something you know works such as a radio. If that won't come on either, then the problem is the outlet, not the kiln. If the outlet works then the next thing to check is the kiln's fuse. The fuse is located on the back of the kiln near the power cord. Unplug the kiln and remove the fuse by pressing on the fuse holder and turning counter clockwise half a turn. Fuses are cheap. Take it to the hardware store and they can get you another like it. Once you have replaced the fuse, try powering up the kiln again. If you know the outlet and the fuse are good and it still won't come on, then it may be time to contact your manufacturer for additional help.
What's a thermocouple and why do I need to know?
The thermocouple is the little wire poking in from the back of your kiln and it senses the temperature inside the kiln. You need to know enough about it so that you don't accidentally interfere with its operation. The thermocouple needs to extend half an inch or so into the kiln. If it gets mashed back into the muffle then the muffle, doing its insulating job, will prevent the thermocouple from getting an accurate reading. You tell the computer to fire to 1400; the thermocouple, sitting insulated back inside the muffle is only getting a reading of 500 degrees and tells the computer to give it more heat. Before you know it, the kiln is at 2000 and you've got a puddle of melted silver. So make sure you don't smack the thermocouple with a shelf or anything else when taking stuff in and out of your kiln. Likewise, don't have anything touching or blocking it from getting an accurate reading during firing. If you set up a shelf directly in front of the thermocouple or have a piece sitting too close to it, this can act as a heat sink pulling heat away from the thermocouple and giving the computer inaccurate readings to work with. Picture half and orange sitting over the thermocouple and keep that area clear of anything during firing.
I got an error message or I've reached a point where I need help. Now what?
BEFORE you call your distributor, manufacturer or kiln repair professional, write down the following information. They will need it to help you.
- Error message, if any.
- Temperature when error occurred if possible
- From the data-plate on outside of kiln on the right-hand side.
- Serial number S/N
- Part number P/N
Reaching this point is very unusual though. These ceramic fiber kilns are very reliable, hard working kilns and should provide you with years of maintenance free use. Hopefully knowing a bit more about how they work will help you get even more use and enjoyment from your kiln!
Pam East is an authorized Paragon distributor. Please contact Pam for all your kiln needs and questions.
(A slightly expanded version of this article with photographs will be appearing in a future issue of Art Jewelry Magazine. I will make an announcement when the issue date is determined.)