Newbie firing schedule questions...!

[NRichards]

Hello Everyone,

Hope you all had a good Christmas and new year?

I welcomed the new year in with my first firing of my Paragon Fusion 16. I used the following schedule that I'd found on here:

1) rate - 200 degrees per hour to 640 degrees c, hold for 60 mins
2) rate - full, to 820 degrees c, hold for 12 mins
3) rate - full, to 560 degrees c, hold for 30 mins
4) rate - 10 degrees per hour to 520 degrees c, no hold 0 mins
5) rate - full, to 20 degrees.

Is it correct that it should have taken 22.08 hours for the whole firing? I know each kiln is different and that local voltage variations can have an effect but I had no idea it would take this long!

I used two layers of float glass (30 cm x 30 cm) with some bits of coloured glass in between (not sure what kind of glass) and for a first firing I'm pretty happy even if it did crack; I'm putting this down to either my not cleaning of the glass properly or an incompatibility with this particular piece of coloured glass.

Can anybody share some information on firing schedules for different kinds and sizes of glass and a rough idea of how long they take? I have had a good look through the Firing Schedule page on here so maybe I missed it if it is there.

Thanks in advance and I wish you all a happy new year!

Naomi

[Zeldazog]

My kiln, a Hot Start Pro, takes anything from 112 to 17 hours for firing usually - a lot of it is how long it takes the final cool down = your kiln is firebrick, which is very efficient, and holds heat well, so takes longer to cool down.

I don't know where you got your schedule from, but it's not right unless you have an extremely thick piece (over an inch)

Assuming your piece is of a "normal" thickness, as in around 6mm, and isn't too large (and 30cm is fine), try this:

Rate 1 and 2 are fine until you get to know your kiln (I fire Float at 835 for a full fuse, but each kiln is different)

3) rate FULL to 517, hold for 30 minutes
4) rate 83 DPH to 371, no hold
5) rate FULL to 50 degrees

This is actually same as Bullseye for the annealing zone, but it covers float just fine.

The schedule you have used has potentially gone way too fast through the anneal cool down, which is rate 4 here. And rate 3) in the schedule here is pretty pointless as far as I can see (unless it's for casting??) And there is no need to program it down to 20 degrees final cool down, I open my kiln at 50 degrees.  It's actually now programmed to cool down to 100 degrees, because it's normally on overnight at the studio, so by the time I get there in the morning, it's reached ambient temperature anyway - but that sort of thing will make a difference to the program time.

The crack could have been caused by glass incompatibility or too fast a cool down - unlikely to be cleaning, that would leave scummy marks, but doesn't usually cause breakage in my experience.

[Zeldazog]

Naomi, you might find it useful to browse this site too:

http://www.warmtips.com/Cat1.htm

[NRichards]

Hi, thanks for your quick reply. I'll try your suggested firing schedule in my next firing. I take it its safe to leave it firing overnight then? We're on an electricity key so it'd be cheaper if I did that!

Is this firing schedule OK if I then want to slump the glass into a square bowl mould? Do you know any for that?

I hadn't realised you'd be able to open the kiln at 50 degrees, I guess you still have to leave the glass in there to cool down? Does it matter what the room temperature is at all when you take the glass out?

Thanks for the link as well, really useful info there.

Thanks

[Zeldazog]

There should be slumping schedules on the Warm Tips site, also look at Bullseye http://www.bullseyeglass.com/education/

You really need to get to know more about glass process temperatures, if you try and slump at this schedule, you'll have a misshape piece of glass in the bottom of your mould...

I can't remember my slumping schedule of the top of my head, but you'll find plenty of guides out there to use - although, do note that every kiln is different, even two of the same model can be different, so do get to know your kiln (again, I think it's the Bullseye tip sheets that show you how to test all areas)

Unless you're out in the arctic circle, 50 is fine to open your kiln, I get my glass out as soon as I can touch it.

[NRichards]

Brilliant thank you! I've just started another firing of float glass with your suggested firing schedule, fingers crossed! I think my first attempt must have cooled down too quickly and been incompatible, when I looked at it this morning it had cracked by its own accord just sitting on the side in the utility.

Thanks for all your help.