Sunday, November 14, 2010

And Now A Word About Kiln Shelves

I used my old shelves for the bisque, but they are not ideally sized for the larger dimensions of my new kiln, so in the interests of efficient firing, I'll need to buy some which are better suited. (It is a bit of wisdom here in Maine that "boat" is an acronym for "Bang Over Another Thousand;" it is starting to seem to me that the letters K-I-L-N stand for "Kick In [your] Last Nickel.") I won't have to replace all of them, but unfortunately my newest, straightest shelves are cordierite, also known as mullite. Sad to say, these are not appropriate for soda firing, as the soda vapor will attack the shelf material "aggressively" according to the nice man at Continental Clay, whose name I have forgotten. If I wanted to use them, I could coat the shelves on both sides with a high-alumina wash, but that sounds like a guarantee of little flakes of kiln wash all over the pots; fuggeddaboudit. Anyway, my options are:

  • Regular silcone carbide shelves. These are the black shelves you always see, usually warped. Heavy as all get-out, too. These are about $125 for a 12 x 24 shelf; I shudder to imagine what the shipping cost would be.

  • Nitrite-bonded silcone carbine shelves. These are those skinny (or skinnier), lightweight shelves with the little slits on four sides, called expansion joints, which are intended to prevent (or, really, delay) warping. As these are both lighter & cheaper than regular silicone carbide - and billed as no less strong - they seem like an obviously better choice. So obvious that I almost feel like I am missing something: why would anyone buy regular silicone carbide shelves? The nitrite-bonded are about $75 for a 12 x 24.

  • Alumina Kiln Shelves. These are billed as an economical alternative to silcone carbide, and they are cheaper: I found prices ranging from $34 to $83. They are an inch thick and weigh a bajillion pounds (or, you know, 22 lbs: close enough.) Still, the difference between $34 and $75 is not inconsiderable since I will have to buy maybe 8 shelves....Hmm.

  • Advancer. A girl can dream! These litte beauties weigh less than 10 lbs for a 12 x 24, and are only 5/16ths of an inch thick. Sadly, they are probably ("probably," she says, ha-ha.)out of my price range, at $175 each. I admit a great temptation, however: I am not particularly burly, and not getting any younger (looks can be deceiving!) and I hate to think of how I will load 20 years from now. Maybe I will hire a buff assistant. Yeah, okay, an assistant would be even spendier than fancy shelves, so maybe not.


Hollis Engley said...

yeah, I'm thinking the same thing. Do I really want to spend $2,000 minimum on the shelves I'd need for my teeny-tiny 17 c.f. kiln? Probably not. But looks are not at all deceiving with me, and it's clear I need to think about something new soon, if only because these shelves are in their last days. I don't envy you the choice.

Brian said...

A timely article - good info.
I'm in the midst of looking at shelves for a fiber kiln I'm planning and was looking at the nitride shelves, but then saw the manufacturer warned against uneven heating and faster than 'normal' temp rise. Bummer, so I then thought ok, I'll use a regular cordierite shelf on the bottom. And guess what? Same story. I certainly don't want to shatter a $150 shelf, but how much of this is the manufacturer just covering their butt?

Lori Watts said...

Brian -- I don't know the answer to your question, but I can contribute one piece of information: I have twice destroyed nitrite shelves in a raku kiln (I'm a slow learner, I guess) but have never cracked a cordierite shelf in the same kiln, though I use them regularly.

Brian said...

Lori - That's _very_ helpful info. Thank you!
I figured as much on the cordierite shelves, since that's all I've ever seen in raku-fast fire kilns, but wasn't sure how touchy the nitride shelves were.
Are yours the solid cordierite, or the hollow corelite? I'm leaning toward corelite to minimize the thermal mass of the furniture and get more heat into the ware.

Lori Watts said...

Brian -- I've never ehard of hollow kiln shelves. How interesting!

Hollis -- I am thinking of getting one advancer shelf per year. Since I really only need them for the chest-high-and above layers, I should have all the necessary shelves before I am decrepit. I hope.

Brian said...

I came across them while researching, They have channels in the middle, almost look like corrugated cardboard structure.
Google 'corelite shelves' - a number of places sell them.
Also saw yesterday that Bailey is not recommending nitride shelves for electric oxidation anymore

Marshall said...

We sell both Advancer and traditional oxide bonded, silicon carbide (SiC) shelves here at Smith-Sharpe Fire Brick Supply ( We sell Advancer shelves specifically tooled for use in electric kilns and have many happy users. I have heard that regular nitride bonded SiC shelves have failed in electric kiln applications, and this is probably why Bailey is no longer recommending them, but Advancer is not simply a nitride bonded SiC. Advancer is an advanced, 5/16" thin, silicon-nitride bonded SiC shelf that is fired twice to get unique properties not found in traditional nitride or oxide bonded shelves. We tested extensively with Skutt Kilns before bringing these shelves to market, and have since sold many shelves to electric kiln users including potters and production tile makers. It is true that they are considerably more expensive than cordierite, but they will stay flat even under heavy loading at temperatures of cone 10 and higher. At 5/16" thick it is possible to load more work and achieve quicker firing cycles due to the reduction of furniture mass.

All this may sound a bit boring and technical, but I think you get the idea.

We also sell the traditional, heavier silicon carbide shelves for considerably less money than the $125 figure you have named. They are NOT nitride bonded, they are oxide bonded and have proved to be an all around workhorse shelf providing many years of service in reduction, wood, soda and salt.

I just wanted to set the record straight!

Anonymous said...

I've used Advancer shelves before and they are AMAZING but it is hard to get over the cost even for all of the advantages Marshall mentions. I'm in the market for some shelves (10x21) for a small soda kiln and trying to figure our which way to go.

Lori Watts said...

YOu got that right! Still I think ia am going to buy a few advancers - one at a time - for the higher levels in the kiln. Apparently they don't need scraping? The labor saved might make them worth the expense.

Unknown said...

I broke my upper arm in October. The thought of holding a heavy shelf out in front of me at shoulder height without dropping it on my students' ware (and mine) is frightening. I just took delivery of four Advancer shelves which will join the four silicon carbide shelves with the slits. I will use the heavy silicon carbide and cordierite shelves for the bottom few layers. Hoping I am all set for the foreseeable!