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An Update on Viewing Witness Cones


Placed about 18

CONTENTS

An Update on Viewing Witness Cones

Basic Kiln Maintenance Seminar October 17 – 18

Recent Q&As: Testing the accuracy of a digital controller

A Kiln Story: The Fired Pretzels

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AN UPDATE ON VIEWING WITNESS CONES

Recently I experimented with viewing witness cones through a peephole. I wondered if it would be possible to see them with a cell phone camera and therefore avoid the direct glare of the firing chamber.

I positioned the cones on a shelf in a Paragon TnF-23-3, fired to cone 7, and placed my cell phone in front of the peephole. The camera could not register an image even when filtered with green firing safety glasses. However, a Canon Rebel digital camera picked up the image of the witness cone, which I am including with this Kiln Pointer. The firing safety glasses that I placed in front of the camera removed some of the glare.

I found it easier to see the witness cones without the aid of the camera, though. You may need to look through the peephole at different angles to see the entire cone especially if the cone is close to the peephole.

Here is a previous Kiln Pointer with more information that I just added:

Most people have difficulty seeing the witness cones on the kiln shelf during firing. But if you position them just right, you can see them even at cone 10, when the kiln interior turns white-hot.

Being able to see the cones during firing is your assurance that the kiln is firing normally. If the kiln takes longer than usual to fire and you cannot see the cones, you may worry that something has gone wrong. Maybe the kiln is even over-firing.

In formulating these guidelines, I tested a welder’s facemask, mirror, and high intensity flashlight. You don’t need those items, even for cone 10 viewing.

1) Place the cones 8” - 12” or more away from a peephole. Positioning them closer makes them difficult to see.

2) Have enough space around the cones to keep them from touching a piece of ware when they bend.

3) Position cones so that when viewed from the peephole, they are silhouetted by an element on the opposite kiln wall. (Keep cones at least 2” from an element.) The element that silhouettes the cones should be level with the lower part of the cone. If the element is in line with the upper part of the cone, the cone will disappear from view when it bends.

4) The center elements in some kiln models do not glow brightly even at high temperatures. In this case, position the witness cones level with a top or bottom element. The element must glow brightly to silhouette the cones.

5) If you use the three-cone system, always have the higher temperature cone on the same side in every firing. Otherwise you can lose track of which cone is which.

6) Wear firing safety glasses when viewing the cones through the peephole.

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Basic Kiln Maintenance Seminar October 17 – 18

We are holding a 1-1/2 day Basic In-Plant Kiln Maintenance Seminar in Mesquite, Texas on October 17 - 18, 2008. Mesquite is 30 minutes east of Dallas. You do not need to bring tools.

The seminar includes two lunches, one restaurant dinner, and a 3-ring notebook of maintenance data on Paragon kilns. For more information call customer service at 800-876-4328 / 972-288-7557 or send an email to info@paragonweb.com . Ask about Paragon’s airport and hotel pickup schedule.

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RECENT Q&As

Q. I have a glass kiln. Is it worthwhile to check the accuracy of the digital controller with a pyrometer?

A. The pyrometer may be inaccurate, too. If you had two pyrometers, you would likely get two slightly different temperature readings.

If the controller is inaccurate, it is probably actually the thermocouple that is off rather than the controller. Even new thermocouples can vary a little.

One of the main advantages of the controller is that it fires consistently from one firing to the next. But you may need to alter the temperatures from a recommended firing schedule to get the exact results that you want.

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A Kiln Story: The Fired Pretzels

John Toki in Berkeley, California wrote, “A customer called to tell me her kiln was disintegrating and that the kiln bands were literally falling apart. Handfuls of iron chips were mysteriously falling near the kiln stand after a firing. I asked her, ‘Did you do anything different from your other firings?’ She replied, ‘No.’

“I consulted with a metals expert and the kiln manufacturer without an answer to the problem. We continued to send new parts and sheet metal bands to the customer. A year and a half later, Bryan, Leslie Ceramic’s general manager, was talking to the customer. She said, ‘Bryan, you should see those sculptures my son is making by dipping pretzels into clay slip.’

“Bingo! That was it. The salt from the pretzels combined with moisture was migrating through the kiln brick and causing severe corrosion to all metal parts. Mystery solved!”

(John owns Leslie Ceramics and co-authored the recently revised 640-page “Hands in Clay.”)

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The intense summer heat is about to begin here. I learned to adjust to it during my childhood days in Tripoli, Libya. At first the heat was stifling, because I had moved there from Alaska. But eventually I could even walk bare-footed on the hot sand.

I hope you are enjoying your summer.

Thank you,

With best wishes,

Arnold Howard Paragon Industries, L.P. – Better Designed Kilns 2011 South Town East Blvd. Mesquite, Texas 75149-1122 Voice: 972-288-7557 & 800-876-4328 / Fax: 972-222-0646 ahoward@paragonweb.com / www.paragonweb.com

PRIVACY NOTICE: Under no circumstance do we share or sell your email address.

Copyright 2008, by Paragon Industries, L.P.



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