Observation hole Plugged?

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    Hi everyone. Have already learned so much as a newbie combing over questions/answers on this forum. Thanks for all your comments!

    I did my first bottle slump and my glass kiln seemed to take forever to get to the high temp of 1430. I have just purchased this used Olympic kiln and there was not a peep-hole plug with it. Do I need to plug the observation-hole (it’s cone-shaped) at the start of the firing or when I get to a certain temp to retain the heat to ramp faster?  One bottle on a flat slump did pretty well, the other in a mold was dull and seemed to devit.

    Also, I used the body firing setting and think from reading comments here that I should have used the top lid for firing?



    From everything I’ve read (much) and in my experience (somewhat limited) the hole does not need to be plugged. Only a minimal amount of heat will escape through the hole.

    Likely you can order a plug from Olympic. I have two kilns, and don’t use the plugs in either.



    That’s correct. At fusing temperatures, air expands considerably resulting in a very thin atmosphere in the kiln. The lack of air means there isn’t anything to carry a lot of heat through the hole.  The glass, on the other hand, is  heated by radiant heat (line of site from the coils) so the absence of a lot of air isn’t an issue.

    If you want to plug the hole, some scrap fiber blanket or paper will do the trick.

    Helios Kiln Glass Studio


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