Gas kiln - Not reaching temp.

[valentina]

Hi! I have a question that's probably a bit silly... but can the temperature in the kiln really vary that much? This is the third time I've tried, using two different type k thermocouples, to fire high-temperature samples (1180-1200°C), and in none of them do the glazes seem to vitrify. In the last firing, I took it up to -in theory- 1240°C, but when I opened the kiln, nothing turned out right. I know the best thing to do is use cones, but I don't have any at the moment, so I'm relying on the thermocouple. My kiln is gas-fired made by me. I attach here some pictures of it. I didn't make a peep hole in case of using cones... should I make it?

 

Here's how I set up the interior of the kiln. Since the upper shelves are perforated, I used a solid one as the first layer so the heat from the burner wouldn’t be too harsh... and the thermocouple was placed below that shelf... could that have been my mistake?!

 

Thank you in advance!

 

Edited 6 hours ago by valentina

[Mudfish1]

Hi Valentina. I had a similar issue in my gas kiln, and one of the other Forum members told me that pyrometers aren't very accurate at those high temperatures. If you read the instruction manual for your pyrometer, you may discover that the reading has a lot of uncertainty. I started using the pyrometer to just tell me if things are getting hotter or colder inside the kiln, but I rely on cones to indicate the real temperature I achieved for purposes of maturing the glazes.

You mention this yourself, and I think you are right - you also have your thermocouple in the hottest part of the kiln. The upper parts of the kiln are probably much cooler.

I might suggest putting in cones for your next firing, and then comparing what your pyrometer says to what the cones indicate. Also remember that cones represent "heat work", which depends on both the temperature and the length of time your glazes experienced that heat. Depending on your firing schedule, the pyrometer itself can't tell you if your glazes have matured.

You mentioned putting in peepholes - I would say they are essential! 

Last comment - your kiln looks awesome! Was it hard to build? How did you do the lid? Is it insulated on the inside?