Two shelf firing
- January 9, 2012 at 11:14 pm #9741
I have just taken out two shelves full of little glassy balls and fired shapes of glass from my kiln. They were fired one above the other on the usual cermaic shelf blocks (square 1″)
The top shelf of glass melted and did what it should, the one underneath hadn’t. Do kiln shelves have to have a certain distance between them for the heat circulation/distribution and what would that be?January 10, 2012 at 2:24 am #12382terrapaxstudioParticipant
Ceramic artists have a big advantage over glass artists when it comes to using space in our kilns efficiently. It is common practice to double stack, or more, when you fire smaller ceramic items, usually in the bisque stage. It works just fine.
Glass is not so accomodating. Glass requires a much more even distribution of heat above, below, and all around it, in order to behave in a cohesive manner. If that distribution is interfered with, the result will be an uneven fire.
When you double stacked your small glass pieces, you interupted the flow of hot air circulating in your kiln. Heat rises, so, much like an old oven, the top “shelf” got much hotter than the lower one. I am assuming your kiln has lid elements in addition to the ones in the side. That is one big difference between ceramic and glass kilns. Again, this is because of the need to control an even heat when fusing glass. If this is your case, than the problem is made worse because the glass on the top shelf is also now closer to the lid elements than the ones on the lower shelf.
Basically, there really is no good way to do what you are trying to do. I would advise to accept the fact that a glass artist does not have the luxury of double decking, and you will be much happier with your nicely fused single layer of equally heated glass beauties. Good luck!
Cynthia Ann Swan, Terra Pax Studio, Los Angeles, CAJanuary 10, 2012 at 8:30 am #12383
I have an SC2 Paragon Kiln that is meant for glass, metal clay and ceramics. The element is in the kiln itself, at the back.January 10, 2012 at 8:25 pm #12384terrapaxstudioParticipant
I just went online and researched the heat distribution problem you are experiencing in your kiln. This is the newest comment from Paragon:
The SC-2 has been in production since 1997. It is a proven design that we have steadily refined every year. Our most recent design offered heating elements configured as such: The fast firing element is embedded in the firing chamber shell. The SC-2 heats from the top, bottom, and two sides. The SC-2 includes a 1/4″ thick ceramic fiber shelf.
We have just redesigned the kiln for improved heat distribution. The new design has two separate heating elements in the left and right sides of the firing chamber. The back of the chamber has no element. Extensive testing shows that the heat distribution in the new SC-2 is more even throughout the firing chamber, because heat does not build up in the back of the kiln.
I don’t know when you purchased your kiln, or if you acquired it new or re-fitted model. Perhaps, if it is not the newest model, this could account for some of your heat issues.
Personally, I still think that you are trying to do something the kiln was not intended to do. Your firing chamber is very small, and heats rapidly. Add to that the proximity to the elements question, insulating qualities of the ceramic fire, and the small amount of glass you are heating, and I am not surprised at all that it is difficult to control the factors involved. I still recommend just doing a single layer. After-all, with this kiln, it fires in minutes anyway, so what is the rush?
Hope this helps.
Cynthia Ann Swan, Terra Pax Studio, Los Angeles, CAJanuary 10, 2012 at 9:40 pm #12385
I have an older model with the element inside the kiln at the backJanuary 19, 2012 at 10:47 pm #12386JolindaParticipant
My first kiln was a Skutt G-27 I believe which is a ceramic kiln holding 3 or 4 shelves about 22″ in diameter. It came with the glass studio I purchased and so I had to work with what I had. I now have several kilns, including a very large one just designed for glass but I must be a rebel here and say that I’ve had many successful 3 shelf firings in the Skutt ceramic kiln for fused glass, and one 4 shelf firing which also turned out fine. One needs to understand the principles of firing and the flow of hot air. I carefully put the pieces which are larger and will require the most heat, or composed of “denser” colored glass (white, cream, etc.), or thick and damned, onto the top shelf. I leave as much room as possible between my shelves and as there are no top elements in this kiln I don’t have to worry about stacking toward the lid and it’s problems. And the lower shelves are for pieces that are faster to mature and require a longer, slower firing schedule. I always leave almost double the soak time recommended when I’m multi layering my shelves and it took me a few firings to understand the need for a very different firing schedule to accommocate the more complex nature of multi shelves. But for production glass…it’s great as it will fire the same amount of glass pieces to completion as my Big Bertha (27 x50″) but it cools down almost a full day faster.
In general the advice you have been given here is good and solid…but some of us are rebels and just have to push that envelope…
Windows listen attentively for the sound of broken glass.January 27, 2012 at 9:23 am #12387josthingsParticipant
I have a Jen Ken kiln at home and a selection of Skutts at the studio I teach at.
I have (when rushed trying to get ready for a show fired two shelves, hard to do in a shallow kiln, the top had pendant blocks that needed a full fuse and the bottom where fire polish, it worked out really well, but I know my kiln. I know how hot she runs and when to push her. The Skutts we load up when firing pottery with plates under bowls and cups in the bowls as long as it does not have glaze on it.February 17, 2012 at 6:08 pm #12388lorraineParticipant
I have a paragon 7 and a paragon GL24TSD. In the little paragon 7 i regularly fire a tack fuse on a shelf beneath a full fuse and a slump beneath a tack fuse.
In the GL24 i can do a slump with a tack fuse by shielding the slump with a kiln shelf above and various shelf props around, and the same with a full and tack fuse. I also have ceramic kilns so have a lot of shelves and shelf supports which helps.
Some of my ceramic pieces are fired for a 3rd time with lustres which require a maturing temp of between 600 to 800C i slow down the firing rate to accommodate the needs of the ceramics and then put them in with the glass at either a slump or drape firing.
With electricity prices getting ever higher we need to be adapting to try to minimise the costs especially for me as i run an art and craft club and am usually firing both glass and ceramic kilns 3 to 4 times a week.February 25, 2012 at 4:26 pm #12389redheronParticipant
Hi, I have a paragon 3 year old SC2, and I aways fire two shelfs. I put 3 inch post between the ceramic shelfs. The results are slighly different on both shelfs but I use that to my advantage. Avoid putting glass too close to the door. It is always cooler there. Haven’t tried it yet on my larger Paragon. I just purchased it in the the new year. It takes so much work to make up a load that one shelf has been enough. I fire 5 days a week to keep up with my show demands and it hasn’t effected my electric much. The small one only cost me $1 a fire and the big one $2.50. Happy glass melting. donnaFebruary 28, 2012 at 9:11 am #12390lorraineParticipant
Here in the UK our gas and electricity prices have quadrupled in the last couple of years so and my electricity bill is huge, so need to economise as much as possible. It is happy glass fusing until the electricty bill arrives!
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