kiln questions - front loading

Steve, I have 2 kilns. One front loading 48" H x 25" wide x 35" back. The other top loading 27" high x 51" wide x 39" back. Both have only side elements, but we use them mainly for bending and slumping (convex glass only, not plates, bowls etc.) from 1130F to 1330F, although they will go to 1650F and 2100F respectively. I notice that besides the normal cooler spots near the floor and top, the middle front and back in the big kiln is cooler, with heat concentrated in the corners. It is most likely that a smaller kiln like you are considering (especially in the height) would see less problem with this, but for fusing etc, I would consider that top elements would be most beneficial for even heat. Maybe it doesn't matter, it will be interesting to see what fusers think. Best regards, Les

I have the Paragon TnF-J-14-1 which is the same size cavity with ceramic fiber lining and elements on sides and back (12-key, max temp 1700F). I bought it through Bullseye, a prominent glass manufacturer--they use it in their shop and classes. In their fusing tables, they recommend initial ramping of a side firing kiln to be 1.5 times more slow than a top firing kiln. I've tried it with good results. I agree with the other poster that the small size of the cavity means uneven heating is less of an issue. If I were to get a larger front loader from Paragon, I'd get the GL18 or GL24 with top, front, side and back elements.

I'm not sure what the lining is in the kiln you're looking at, but if it is firebrick meant for ceramics, it may not cool fast enough and cause devitrification. Bullseye states that their glass is less prone to devit, but I've had some pieces do it even when using their recommended schedules.

Cheers, Dianne

After reading Diannes post, I should correct a possible misunderstanding. My kilns have elements all round the 4 sides.

Interesting, Diannes comment re slower cooling and devit. I have never had that problem with slow cooling. I just programme them for night cooking, and let them cool naturally after a run. Maybe it is a problem from higher casting / fusing temps ? Has only ever been very minor with tin bloom, but I don't think there is very much that can be done to prevent this. I have fire bricks in both kilns, one a very heavy dense brick, the other much lighter. If I ever build / have one built myself, I way just use FC board and blanket.

Regards, Les

I've read the contributions of Dianne and Les to this question and found them helpful -thought I would add my perspective.

I am on my third kiln now. I started with a front loader (18" x 18" x 18") which was heated on three sides (i.e. no elements on the door). It was a pottery kiln and I bought it because it was cheap and it was available (not being a big second hand kiln market where I live). For fusing and slumping, I found two major problems. The first was a significant temperature diferential top to bottom and front to back. According to my pyrometer, the top of the kiln was 30 - 50 degrees hotter than the bottom and the edge of the shelf near the door was 15 degrees cooler than at the back. I saw these temerature variations replicated in fused pieces. The second problem was caused by crash cooling (as one is advised to do) - that is to quickly reduce the temperature below the devitrification temperature. With a front loading kiln this means opening the door which allows hot air to escape from the top and cold air to come in from beneath. I found this sudden temperature change often cracked ceramic molds I was using for slumping. Notwithstanding these problems, the kiln was a reliable old workhorse which was generally fine for casting, pot melts and working with float glass.

I am currently using two top loading kilns - one has side elements as well as elements in the ceramic brick lid and the other side elements and a fibre lid. I find the top elements give a very even temperature across the whole shelf - the major problem is the occasional tiny fragment of brick which falls out and inevitably lands in the middle of the most prized piece.

Hope this helps

Gordon

Yes--it happens when I do the full fuse program with a soak at 1500F (Bullseye recommended). There has been some minor devit with two of their newer colors--cranberry and coral cathedrals. With a ceramic fiber kiln, crash cooling is not really necessary (I've tried it both ways), so I may use devit spray if I continue to use those colors. I'm still learning, but there's no teacher like experience. :)

Cheers, Dianne

Thanks everyone for your help. I am guessing I am in for an interesting but exciting learning curve.

The big problem with a front loader when slumping or fusing is you can not see what's going on in the rear of the piece. My first kiln was a front loader and I had to turn pieces around to see if I got a full slump. Top loader is better for this kind of work.

Wrong

I slump a stack of 8 shelves at one time in my frond loading kiln , and all come out perfect

cheers

Jason

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What about the blast of superheated air when you lift the lid for a peek? I guess you don't peek...... so why not drill a peephole in the back of your front-loader? It seems to simple and obvious a solution, so I reckon you had a reason not to. I love my front loading, ancient Paragon GL-22 .... though heating isn't perfectly even, I have yet to see any kiln that is. The newer GL-22 with elements in the sides and front would seem ideal IMHO.

Full truth requires that I disclose that my favorite kiln of all is my home-built 29x59" bell kiln .... I lift the top 'box' with a brake-winch and can hold it open 2-3 inches this way and lose almost NO heat in the process, while allowing viewing or glass manipulation from ALL sides. Now THAT's a goooood design .... going to use it for metal enameling shortly. I've even used it to cure powdercoating.

Such useful devices.... I once used the Paragon to melt the cheese on an omelet.... but that's another story....hahahahahah.

Regards, Jacques Bordeleau

Haven't been here in a while, but I'm glad to see the "sundog" is still around.

Just wanted to mention that some commercial kilns (like my Jen-Ken 28") has multiple quartz windows that allow me to watch what's going on to my hearts content without opening the kiln. I use InfraRed protective eye protection when viewing for any length of time (infrared radiation can cause cataracts over time).

Hey Glenn! Where ya been hidin'? Heheheheh .... actually I am come and go, hit or miss, and I miss a lot. I totally envy your quartz windows for your kiln. I was at an enameling workshop recently and there was a 2" window into the big box... about a 6x6' front loader. That quartz window is sweet, but isn't it a heat loss that feeds the uneven heating of any kiln? I didn't notice great heat from it when peeping in, but have to assume. They just had it uncovered all the time, but I would think a metal flap over the outside would help some. Anyway, it was great to use one in practice instead of theory. My next kiln (or kiln remodel) will have at least 1 quartz window ... very happenin'...;-)

Cheers, Jacques Bordeleau

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I slump compound curved lamp pieces over molds. I can't see the back. This is important to me becauce the glass needs to be centered and fully slumped. I find this is ALOT easier to do with my top loader. If I need to fully open the lid to "play" in the hot kiln I wear eye protection,and welders apron and half jacket. Oh, I turn off the kiln, too.

Hey doggy! I've been toying with a return to copper enameling myself. What brand of enamels are you playing with? Are you using the same as you do for glass? Have you found COE to play as large a part as with use on glass? m

Hey Michele ....( aka > she who walks among clams )... ;-)) I have to make a rather huge shopping list and get stocked up. I have some excellent black ground coat now, and also a white, from Ferro, that we used at the workshop w/ Killmaster and Berfield ... (bought up some leftovers). They seemed to use Ferro more than Thompson, but both are excellent suppliers, and we had materials of all kinds from both places. Also I have a bunch of Bullseye COE glass enamel frits from Thompson that I ended up not using at all for that monster wall project a while back. I'm not too eager to try them thick on metal .... but they might work.... test test test! I know I could sprinkle it on, but not heavy. One thing we determined (I had already determined for myself) was that COE was a minimal worry factor for use of thin colors, such as enamel crayons or water colors, or other thin coloring agents, used over heavier color backgrounds, and that one should feel free to experiment freely without too much worry, unless adding heavy layers of color .... which requires COE awareness and rules. I pretty much say the same for glass or metal enamels, vitreous paints, et al..... test it out and see. Actually, come to think of it, the first vitreous glass painting I did was with a small jar of black 'china paint' that I used to create some excellent sillouettes .... worked so well I researched things and began acquiring a more 'correct' set of enamels for glass, and the methods to use with them. Of course I don't follow 'the rules', but I feel it's important to know what the rules are 'supposed' to be before you venture forth into uncharted territories....hahahahahahah. I really have to get a set of the crayons (or make them), and also the water colors (subtle effects) ... and a full palette of basic color frits for mixing, screening, spraying, etc .... and some ready "ground in oil" color frits would be nice as well, in little jars. The list goes on.....

This is gonna cost some $$$........... heheheh. I'm working larger than jewelry level BTW...... I may try my cheesy 50's porcelain enemel kitchen cabinets.

Regards, Jacques Bordeleau

"If the shoe frits, fire it"

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