Molds to large for kiln?

[Deive Butvila]

I just bought, but have not yet received, a Jen Ken AF3P ProFusion 16 fiber kiln with inside dimension of: 16" x 16" x 5". There is no shelf so need to use fiber paper on the bottom, kaiser lee board, or lava cloth.

Anticipating the kind of projects I had in mind, I bought a round 10 inch colour de verre casting mold. The instructions for the casting mold say: the mold must be placed on 1 inch posts and must not be placed directly on the kiln floor. It also requires at least 5 inches between the mold and kiln top elements. So, whether or not I use kiln posts, it appears I do not have enough kiln depth to use this casting mold. Would you concur?

I also bought a 10 inch shallow bowl mold and rimmed dinner plate mold which came with no instructions. Should I assume the 5 inch kiln depth limitation would not work with these molds as well?

Does a fiber kiln potentially eliminate the need for kiln posts when working with molds?

Thank you for any and all advise!

[Laurie Spray]

Use the molds.....just fire slower as your glass will be close to the elements. If you call Larry at colour de verre he will give you a program that will work. It is notmthe best situation butnyou can do it. There are 1/2 stilts that will give you the airflow you need for his molds. I also think that if you fire slowly it will be ok with them right on the floor. Kiln wash your floor just as a safeguard.

[charlie]

the reason for the stilts is so that air can escape out the holes on the bottom low spots of the mold. you can use cut up pieces of ceramic tiles, which are usually only 1/4" thick, to get the same effect.

[Laurie Spray]

The colour de verre molds are casting molds and they do not vent out the bottom. The slumping plate mold......if it has holes to vent it needs to be on a small stilt so it can vent but
you usually do not need vent holes on a plate mold.

[Deive Butvila]

Thank you for the good advice. I think I will contact Colour de Verre for the definitive word, but think I may have jumped the gun with grand plans before I even set up the kiln.

Among other things, I bought some Kaiser Lee board to use as a kiln shell to avoid the mess with shelf papers. I think that the KL board may also eliminate the need for kiln posts, but am not yet totally clear on that point. Also, I think I can make a KL mold to make plate blanks if the Colour de verre does not work in my shallow top firing kiln.

As a point of clarification, the round casting mold has no air vents, but both the plate and shallow bowl molds do.

Thank you all and have a wonderful new year!

[Jerrwel]

Does a fiber kiln potentially eliminate the need for kiln posts when working with molds?

Thank you for any and all advise!

Take a look at Laurie Spray's bottomless molds http://bonnydoonfusedglasstools.com/. Seems like you can use the bottom of the kiln this way and get the glass the greatest distance from the elements. As the molds are bottomless you will not need venting.

[Bert Weiss]

Fiber kilns behave differently from brick kilns. The fiber does not hold on to heat like brick does. Consequently it will heat quicker using less energy, and cool faster, at the bottom of the cycle. So, in a fiber kiln, when you need heat to accomplish the curve of your firing schedule, the elements turn on to supply that heat. In a brick kiln, the bricks absorb heat during the up cycle, and then give off that heat when the elements turn off. This creates a different quality of heat. In my 30 years of firing fiber kilns, I find that I have more control than you do with a brick kiln. I can make all the things happen, that happen in brick kilns. I can also make other things happen that are impossible in a brick kiln.

In my front loading fiber kiln, I have a peep hole that is stuffed with fiber blanket. When the kiln is 1500ºF inside (red hot), I can take my bare fingers and remove the piece of fiber blanket. The inside of this single piece of material sees that 1500º. If I were to put a cigarette in my mouth and put it in the peep hold, it would light right up.

When I was planning to build my big fiber kiln, I contracted to use a large brick kiln. In that kiln, I fired 19mm glass to 1400ºF and annealed. This glass had softer edges and much more distortion than I get when firing the same glass to 1480º with a 10 minute hold in my fiber kiln. The big deal here is not the temperature, it is the distortion.

Heatwork is complicated. I'm not really sure, but I think actual temperature is important to reach, especially when fusing. Heatwork is a factor of both time and temperature. So, to reach a particular temperature in a brick kiln, you must subject the glass to the level of heatwork required to get the air to that temp.

[Marian]

Are you in a place where there are no ceramics suppliers? A kiln shelf is pretty basic. Any unglazed ceramic works. A kiln shelf that is too large can be cut on a tile saw, too. Save the extra bits- they are useful for spacers, posts and dams.

[JestersBaubles]

Among other things, I bought some Kaiser Lee board to use as a kiln shell to avoid the mess with shelf papers. I think that the KL board may also eliminate the need for kiln posts, but am not yet totally clear on that point. Also, I think I can make a KL mold to make plate blanks if the Colour de verre does not work in my shallow top firing kiln.

Kaiser Lee board will still require some type of separator to be most effective (even Petra will tell you that). You'll still need to kiln wash or use Thinfire/Papyros, or, use irid glass with the irid side down. Also KLB imparts quite a lot more texture than a kilnwashed or paperlined shelf. If you have not tried Papyros (from Spectrum) you should give it a look -- it holds together much easier and is less of a "mess" than Thinfire.

One of the qualities about KLB that makes it so nice for mold making is its "carvability" -- it can be cut with a putty knife and carved with a spoon. This also means that as a kiln shelf, you will have to handle it *very* carefully to avoid knicks that will show up in the fused glass.

KLB is a great product, but I think you may be disappointed if you use it exclusively for a kiln shelf. Just break down and buy a shelf and some Bullseye kilnwash or Papyros and you'll be much happier.

2 cents, Dana W.

[Deive Butvila]

With permission from Larry at Colour de Verre what follows is his answer to my question about firing their 10" round casting mold directly on Kaiser Lee board in lieu of kiln posts in my shallow top firing fiber kiln. I used 1/2" posts and the results were pretty good without changing the recommended firing schedule. The only issue I had was uneven thickness in the cast piece, but think this may be because I did not distribute the frit and glass chunks evenly enough.

Larry's answer to my original question:

"It is very important that you don't place our molds directly on the kiln floor. Placing the mold directly on the kiln floor prevents hot air from circulating under the mold and creates heat stress between the mold's top and bottom. You can prevent this by placing short kiln posts (or tall kiln posts on their sides) on the kiln's floor and then placing the mold on top of them. I would use kiln posts rather than KL board.

Casting requires even heat. Top element kilns are trying to bake a cake with a broiler. You can work your way around this by reducing the target temperature and slowing the schedules. Also realize that glass color becomes a factor with top element kilns. Darker and opaque glass absorbs more heat. Schedules that worked well for light colored glass might be too hot or too long with dark colored glass.

Keeping all these issues in mind, you should do great."