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I'm about to fire 2 large panel measuring 1metre x 50cm each. One at a time. I'm fusing metals in leaf and foil forms between two sheets of 3mm float. I've placed spacers at each corner to allow the metals to fuse in properly and prevent burnout. My question is do you think this firing schedule sounds ok or should I allow more time over all on each segment? I'm also firing on an elevated ceramic board covered with 3mm ceramic paper.

My kiln fires 55 degree cent. lower than it's displayed temperature so i've allowed for this in the schedule.

138 centigrade per hr c to 168c
186c to 520c soak 30 mins.
466c to 600c soak 10mins.
466c to 865c soak 35mins.
300c to 520 soak 40mins.
30c to 515 soak 30mins.
68c to 38c end

I've used this for many years with out a problem for pieces measuring up to 61cm x 30cm (24" x 12"). I'm a bit nervous about firing this larger panel so would appreciate any advice.
This as a scaled down version. Each panel measuring 24" x 12"

A lot depends on how close to the edges of the kiln the larger glass is. The nearer the edge the more cautious you need to be. I can't fire anything that does not have at least 50mm space from the edge of the kiln in the big one. Smaller ones have tolerance for only 25mm from the edge.

Ah, well there's about 110mm distance gap from the edge on the long sides and about 5mm top and bottom edges. I also tend to reinforcing all side ( about 30mm from the piece with used ceramic fiber paper rolled up, as I've found that my kiln doesn't heat evenly. ( It's a fiber board and brick laser kiln, not really happy with it). I've found that this helps retain heat and fuses all edges completely. Oh and it's a flat bed kiln with elements top element only. Thanks for your response.

I think you are going to have trouble.
5mm space is giving no allowance for the heat falling off at the outside edge. As you kiln heats unevenly, it presumably will cool unevenly.
I would try the schedule on clear glass first.

My mistake, I mean't 50mm (5cm) great Idea to test fire clear.....Thanks Stephen

I think in fahrenheit, and not so much in degrees per hour. If I understand your float schedule, it looks nothing like mine. First, your top temperature is quite high. I would suspect you get a lot of devit going that hot. If not, you are fine.

I would heat at whatever rate you feel prudent, to 615ºC and hold for 1 hour, then take 2 hours up to your top temperature.

Annealing does not change with area, once you get beyond pendant size. My 6mm anneal schedule is:
(you will have to do the math to get to degrees per hour)
> 538ºC hold for 36 minutes
538ºc > 480ºC take 36 minutes
480 > 370 take 24 minutes
370 > 150 take 24 minutes

Thanks Bert, as I said my kiln fires 55 degrees C lower than the controller shows. I arrived at this conclusion by placing 8 cones inside and watching throw the vent hole to see when the 810 c bent. I live in the country side so the electricity supply is erratic and also I know my controller isn't configured properly ( a nightmare scenario that I won't bore you with). I don't get devit. so I'm ok on that score. I'll take a look at your schedule and assess where mine needs to be adjusted. As I'm self taught, I appreciate your knowledge and advice.

Ginny. wrote:Thanks Bert, as I said my kiln fires 55 degrees C lower than the controller shows. I arrived at this conclusion by placing 8 cones inside and watching throw the vent hole to see when the 810 c bent. I live in the country side so the electricity supply is erratic and also I know my controller isn't configured properly ( a nightmare scenario that I won't bore you with). I don't get devit. so I'm ok on that score. I'll take a look at your schedule and assess where mine needs to be adjusted. As I'm self taught, I appreciate your knowledge and advice.

I suggest you get a new thermocouple that is encased in an inconel sheath 3mm in diameter and as long as yours is now. These are not expensive and will last many years longer than a thermocouple with exposed ends.

6mm glass may well anneal with a shut off, depending on how your kiln is built.

Hi Bert
I've decided to increase my schedule in the 615 region and also up to fuse temp like you've suggested. My cooling/ annealing sections are longer so, given the inaccuracy of my kiln I think I'll keep it as it is to be on the safe side and then do a test fire. A thermocouple that is encased in an inconel sheath, I'm not really familiar with equipment and how to install it. Would this require a kiln expert/electrician to fit it?

Ginny. wrote:Hi Bert
I've decided to increase my schedule in the 615 region and also up to fuse temp like you've suggested. My cooling/ annealing sections are longer so, given the inaccuracy of my kiln I think I'll keep it as it is to be on the safe side and then do a test fire. A thermocouple that is encased in an inconel sheath, I'm not really familiar with equipment and how to install it. Would this require a kiln expert/electrician to fit it?

The thermocouple has 2 color coded wires. They are probably attached to a block with screws. To switch thermocouples, you simply disconnect the wires on the old one. (take a picture so you don't forget which screw is the red one and which is the yellow.)Then pull it out of the kiln wall. Replace the new one in the kiln wall and reconnect the wires. This is not difficult as long as you pay attention to which wire goes were. There is no chance of electric shock, as the current carried by these wires is miniscule.

I don't know European sources for thermocouples. I'm sure there are good ones. In the USA, I use a company called Krumor. They are a manufacturer and are willing to sell one thermocouple on a custom basis. You want Type K, inconel sheath, 3mm diameter, whatever length your original one is, with loose wire connections.

Cheap thermocouples have exposed ends. These degrade relatively quickly, and yield readings that are way off, like yours. The inconel sheath, protects the welded end from oxidation. It is plenty quick enough in response time. I have this type of thermocouple in place for over 20 years and I have not noticed any degradation. My programs still work fine.

You've got a couple of issues: First, you're right up against the edges of the kiln/elements on one side and relatively far away on the other, so going slower is definitely in order. With only 5mm of space there's not a lot of room for air circulation on two of the edges. When I'm that extreme I move to a schedule normally intended for 2-3X the thickness until about 260C or so.

Second, the larger and longer your panels become, the more likely you are to get a little bowing up at either end as the glass starts to cool, especially if those ends are hotter than the sides. In some cases the bowing can be extreme enough to add stress and potentially crack the glass.

Your panel proportions are 2:1, and it's more likely to occur as your panels approach 3:1. However, to be on the safe side you might want to add a relax segment in your firing cycle. Get the glass down below the strain point, then take it to 50 degrees above strain point and hold it there for 30 minutes. Then proceed with your anneal. That segment allows the glass to relax and come down fully on the shelf, avoiding stress.

As I said, it's probably not necessary with a panel ratio of 2:1, but if you do see cracks, stress or the panel doesn't lie perfectly flat after firing, try it.

Beautiful work, by the way. Are you adding enamels or is that all leaf/foil?

Bert Weiss wrote:

Ginny. wrote:Hi Bert
The thermocouple has 2 color coded wires. They are probably attached to a block with screws. To switch thermocouples, you simply disconnect the wires on the old one. (take a picture so you don't forget which screw is the red one and which is the yellow.)Then pull it out of the kiln wall. Replace the new one in the kiln wall and reconnect the wires. This is not difficult as long as you pay attention to which wire goes were. There is no chance of electric shock, as the current carried by these wires is miniscule.

And if the temperature goes down rather than up, then you know the wires were connected backwards .

Dana W.

I've managed to fire the panels successfully thanks to all the advice! Cynthia I use a combination of leaf and powders.