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achieving uniform heat-perforated and/or staggered shelves(was:uneven

updated wed 23 jun 04


Kenneth J. Nowicki on tue 22 jun 04

kiln temp)

Hi Cathi,

I'm sure there are more qualified folks on this list than I that can offer
their expertise... but I have been thinking about this kind of thing myself
lately... the air flow in and around the shelves, pots, and kiln furniture during
firing. It seems to me, that the more the air circulates... the more even the
temperature will be throughout the kiln... and assisting the kiln by whatever
means in order to achieve that goal seems like a move in the right direction.

As Steve Lewicky, President of L&L Kiln Mfg. Co., recently posted in his
comments (see message on 6/18 "Re: help needed w/ cone 6 electric kiln") that I am
working directly with L&L on an exciting new project... a brand new custom
built "hybrid" gas/electric cone 10 reduction kiln. We will be modifying L&L's
JD230S-PB (w/3" brick) which when all said and one will leave me with 6.67 cu.
ft. of firing space.

While working towards finalizing the plans for this kiln... this area of "air
flow" has been forefront in my mind. By using the thicker 3" brick in the
kiln, I've gone from a required standard 21" round shelf to a 20" round shelf...
a less common size. At one point I looked into "Advancer" shelves, but at the
present time, they don't make them in the 20" round yet. They do offer them in
the 21" diameter currently, but even though they would fit (albeit very
snugly), I was afraid of what would happen bumping these into the walls of the kiln
during loading and unloading, but even more importantly, hindering the air
flow in the kiln.

I too was interested in perforating my shelves with small drilled holes to
perhaps assist the kiln in achieving a more even firing, however, Steve
recommended against this in the shelves that L&L uses... I'm not sure, but I believe
they are Cordierite, Mullite, or a combination thereof. Steve's concern is that
the holes drilled in these shelves will weaken them, and that many might
break during the drilling process as well.

So, as much as I'd like to see the manufacturers who make kiln shelves start
offering a "perforated" shelf to customers from the factory... it doesn't look
like it is going to happen anytime soon. I have heard that industry commonly
uses perforated kiln shelves, and see no reason why studio potters cannot
take advantage of this and do the same. In my opinion, it certainly seems like it
warrants further investigation. But, for now... I've decided to use mostly
"half shelves" and stagger them... using only one full round shelf on the
bottom. I think staggering them throughout the kiln will be an adequate solution and
offer enough options to pull off just about any firing requirement I might

Cathi, you don't mention what material your shelves are made out of... what
are they? Personally, if it were me and I had shelves that I were willing to
take a risk on... I would find a great drill press and some proper bits for the
job... and give it a go. Might be painstakingly tedious to do, as you'd have
to be very careful while drilling, and I'm sure would be a time-consuming
task... but in the end... it may certainly be worth it all. Your other option is to
get some half shelves and try staggering them. I'm guessing that would help a
great deal as well.

Best of luck to you on this, and report back and let us all know what you end
up with, okay?

All the best,

- Ken Nowicki

In a message dated 06/22/04 typicalgirl@BOX49.COM (Cathi Newlin) wrote:
<The results were *really* uneven, top to bottom and on either side of
the kiln.<>
I am suspecting that my kiln shelves are still not allowing enough air
circulation around the entire kiln, especially on the left side. >Because I
have a small kiln and space is precious, I am hesitant to keep paring down my
Would it be a reasonable alternative to drill a seriers of holes in the kiln
shelves to create more even heat distribution?