From bubbles to thin fire paper haze

childersstudio · Post by **childersstudio** » Thu Sep 25, 2003 5:11 pm

Cynthia,
When I purchased my kiln it came with two fiberboard shelves, each about 28" x 28". As I get more experienced and do bigger pieces I will want one seamless shelf, where do I get such a thing and what do you recommend?

Jackie Beckman · Post by **Jackie Beckman** » Thu Sep 25, 2003 5:57 pm

Well then, you can fit 3 20 x 20 mullite shelves in it. Brock

Yes, that's what I have in mine. Problem - when you need to cross a seem either because your piece is larger than 20" or when you need to lay several pieces out and they need to cross over a seem to fit in the kiln. In this situation, I place 1/8" fiberpaper over the three shelves which are butted up together and leveled, then cover that with thinfire. I bought a large fiberboard to work seemless on, however because I usually fire face down, I'm not usually happy with the surface I get with it. This has been the $64,000 question for as long as I've had that kiln-

J

Cynthia · Post by **Cynthia** » Thu Sep 25, 2003 6:10 pm

childersstudio wrote:Cynthia,
When I purchased my kiln it came with two fiberboard shelves, each about 28" x 28". As I get more experienced and do bigger pieces I will want one seamless shelf, where do I get such a thing and what do you recommend?

I have a Magnaform shelf that is an extruded Unifrax material. It is available through Western Industrial Ceramics in Portland, OR (do a google search for the contact information). It comes in a 2" thickness and is somewhere around 40+ inches by 80 something inches. They will rigidize, burn it out, cut to size and ship for somewhere around 500 dollars...I know, that's a big hunk of cash. It still has some of the problems of most fiber shelves, but less so in terms of warpage, softness, and dimples. It is seamless. The 28" square boards that come with the Denver kiln make nice dams if rigidized and cut into strips...but as shelves, I had no patience for them. That is my personal take on those shelves, but others find them to be simply nifty.

I have done what Charlie does and slathered on the primer thickly. It has worked as Charlie explained and pulls up when it sticks to the glass without damaging the shelf, but I don't want to repair the mars in the surface of the wash or scrape off primer from my glass and deal with the residue that remains on the glass. So I have opted to use Thinfire for the insurance that my shelf will remain unmarred and undamaged (knock wood). I have to try the talc thing and see what I get. Maybe using talc on the shelf at lower temps would keep the glass from sticking?

In response to Brock's post, I thought that Jackie's kiln was a fire brick constructed Paragon which is a different animal than the Denver...Nevertheless, I still assert that using mullite shelves will change the efficiency and firing properties of a fiber kiln...or at least one like mine, and that position comes from my experience with this particular kiln, discussions with Denver Glass when trying to get away from a fiber shelf and others who have similar kilns with similar issues.

It takes more energy to heat a mullite shelf (just like it does to heat brick), than to heat fiber. Fiber reflects the heat more efficiently (rather than absorbing it) compared to brick or mullite, so you don't have to heat anything but the interior space of the kiln. The mullite shelf releases that stored heat at a slow rate as does brick, and the fiber is not retaining heat or give it up at the same rate the mullite will. These different refractories create different heating and cooling properties within the kiln. This isn't my flight of fancy, Those differences in the properties of how the kiln heats and cools are significant and should be understood (Know your kiln tip sheet #...).

Brock · Post by **Brock** » Thu Sep 25, 2003 6:24 pm

. . . It takes more energy to heat a mullite shelf (just like it does to heat brick), than to heat fiber. Fiber reflects the heat more efficiently (rather than absorbing it) compared to brick or mullite, so you don't have to heat anything but the interior space of the kiln. The mullite shelf releases that stored heat at a slow rate as does brick, and the fiber is not retaining heat or give it up at the same rate the mullite will. These different refractories create different heating and cooling properties within the kiln. This isn't my flight of fancy, Those differences in the properties of how the kiln heats and cools are significant and should be understood (Know your kiln tip sheet #...).

I take it back, it's not that it has nothing to do with thermal efficiency, it's that it has everything to do with it. All the heat in a fibre kiln is coming from the shelf as soon as the elements are off. The mullite shelf releases heat slowly, for a long time, increasing the efficiency of the fibre, which would otherwise lose heat to rapidly. Like all of us my experience is peculiar to my kilns, and in my case, the absence of a controller. In MY kilns, mullite and fibre is a perfect combination, resulting in the kiln naturally stalling out around 950 for an hour or so, when turned to low from a full fuse. I know my tip sheets . . .Brock

Jackie Beckman · Post by **Jackie Beckman** » Thu Sep 25, 2003 6:55 pm

Jackie has the same kiln and she uses 3, 20 x 20 shelves and 3, 20 x 8 shelves to fill the space.

Actually, you are correct about my shelves, Brock, but my big kiln is a Paragon - brick sides, fiber roof. I looked into the Denver, but I had heard some caving lid horror stories at the time I was researching (perhaps they've fixed that now) and so I went with the Paragon. It seemed worth the extra $$ not to have to deal with structural issues down the road. None the less - I like mullite shelves the best. And I like em without any fiber paper too. So . . . All I need now is a 28" x 62" unwarped, uncracked, not-too-heavy mullite shelf. (yeah right)

Maybe if I click my heels -

Jackie

Brock · Post by **Brock** » Thu Sep 25, 2003 7:01 pm

Maybe if I click my heels -

Jackie

Don't wear out your Fairy Godmother for something so mundane. Brock

Cynthia · Post by **Cynthia** » Thu Sep 25, 2003 7:12 pm

Jackie Beckman wrote:... my big kiln is a Paragon - brick sides, fiber roof. I looked into the Denver, but I had heard some caving lid horror stories at the time I was researching (perhaps they've fixed that now) and so I went with the Paragon. It seemed worth the extra $$ not to have to deal with structural issues down the road...

Jackie

You chose wisely. The big Denver's do cave in. Don't know if they have fixed that flaw. I think you can have them upgraded...particularly the bell version, but I would have paid the extra for a Paragon like yours if I had only known...or had one custom built like Doug Randall did. I think it was Doug who shared pics of his bolstered up Denver Bell.

Jackie Beckman · Post by **Jackie Beckman** » Thu Sep 25, 2003 7:13 pm

Brock wrote:Maybe if I click my heels -

Jackie

Don't wear out your Fairy Godmother for something so mundane. Brock

What good advice

childersstudio · Post by **childersstudio** » Thu Sep 25, 2003 11:21 pm

What's this about the big Denver Glass kilns caving in? I understand that Denver Glass has had different owners with different results over time. Is the problem of a possible cave-in something in the past or still a concern in the present? I purchased my kiln in January 03, but did not have a place to use it until July. If it is still an ongoing challege for Denver Glass, should I be trying to find a way to reinforce the lid?