[INYA]

Hello,

I haven`t manage to find good porcelain firing curve. I always have big problems with warping. Now I decided to figure this out ... there are three bodies (all "low fire" porcelain, cone from 9-10) in my studio which I would like to try.
I will fire to cone 9 / 10, actually 1240 celsius (I don`t quite understand those cones, there are 6 different temperatures for cone 9). All bodies should be fired above 1220.

I am making test pieces- casting from 2-4 mm.

Another question - has anybody tried raw glazing with porcelain?

Any suggestions?
Where is the crucial point for warping?

Thank you a lot!

[Chris Campbell]

Because there is no grog in porcelain it always will slump, warp and move at high firing temps. It needs to be supported once the shape moves out from being a straight self supporting cylinder. There are many options for supporting it during firing. Another research week ahead!
Controlled cooling also helps eliminate cracks and warping.

[Diana Ferreira]

Our studio manager can fire her kiln almost 7 days a week - another prominent ceramicist in our city referred to her kiln as a microwave. She works with porcelain, fires to 1260C She gets occational warping, but not a lot. and she works extremely thin.

I use spann rings for my work. I dry my cups and bowls upside down on them, and it helps to prevent my work to warp in the drying process.

If your claybody is uneven in thickness, it can pull egg shapes in the glaze fire. If you slipcast, make sure that your slip is not too thick and sluggish when it pours out - this will cause the area that the slip is running off, to be slightly thicker. I know that one is 'not allowed to' but I actually shake my molds when I decant my slip.

[INYA]

Another research week ahead! oh yes, and I am ordering another body from Ireland )

but HOW exactly do you fire porcelain? I can set 1 stop on the way up, the top temperture with hold time and 1 stop on the cooling side.

f.e. 100 C/hour till 600 C

150/C till 1240 C

?


I thought about firing with stilts but I have never tried firing high bisque and low glaze (I guess the principle is to fire high bisque with stilts and low glaze)


thanks!

[INYA]

thanks for the tip about the liquidity and shaking off though

Have to try this!




how do spann rings look like, there are no usuful google hits...

[INYA]

I am attaching picture that macdoodle has just emailed me (Thank you very much)
maybe somebody else would need it...


They look great, this is going to be great testing week

Attached File(s)

•  spann rings_za_susenje.jpg (43.95K)
  Number of downloads: 92

[StefanAndersson]

INYA, on 16 April 2012 - 08:02 AM, said:

Hello,

I haven`t manage to find good porcelain firing curve. I always have big problems with warping. Now I decided to figure this out ... there are three bodies (all "low fire" porcelain, cone from 9-10) in my studio which I would like to try.
I will fire to cone 9 / 10, actually 1240 celsius (I don`t quite understand those cones, there are 6 different temperatures for cone 9). All bodies should be fired above 1220.

I am making test pieces- casting from 2-4 mm.

Another question - has anybody tried raw glazing with porcelain?

Any suggestions?
Where is the crucial point for warping?

Thank you a lot!

Raw glazing porcelain is in some ways easier then stoneware clays; they often shrink less during drying and more in the fire than stoneware. I would recommend dipping during leather hard stag or slightly dryer. If the pot collapse after dipping try adding more water to the glaze mix and try to shake of excess glaze when glazing.
The glaze needs to shrink more then usual to fit well so the glaze recipe should be high on plastic clay (kaolin can be rather unplastic). Adding up to 5% bentonite adds alot of plasticity but many glazes work as is if used at the right dryness of the pot..
If you are unexperienced with raw glazing expect a bit of testing before you get it just right. Good luck!

[INYA]

thanks for the tip about raw glazing

but guys what about the firing curve for glaze firing (bisque before)?

does this sounds ok?
- 480 F /hour until 1472 F
-300F/hour until 2264 F
-hold 15 minutes
-down 300F/hour until 1112 F

thanks!

[Diana Ferreira]

hi Inya, yea that is my spann rings (and black clay work drying on it. I have rings in various diameters, with a gentle curve. If you want to make them, it is better to have a master made of rubber - otherwise it could be tricky to get the spann ring out :-) And I have close to a 100 if not more in the studio.

[Diana Ferreira]

If you want, I will ask Karen tomorrow what her firing range is. She never ramp her kiln down. When it reached temp, and soaked, it switches off.

[INYA]

Diana Ferreira, on 17 April 2012 - 04:53 PM, said:

If you want, I will ask Karen tomorrow what her firing range is. She never ramp her kiln down. When it reached temp, and soaked, it switches off.

PLease ask her about the firing I would really be grateful for that info.

I am quite good at mold
making, I don`t think the mold will be a problem, I am starting doing this tomorow

[neilestrick]

I have never found porcelain to need a firing schedule that is any different than stoneware. I have fired on several different schedules here at my shop with no difference whatsoever. Glazes, on the other hand, will be greatly affected by the firing schedule.

I think the main issues with warping ire the formula of the body itself and the construction of the ware. Some porcelains warp more than others. It just depends on the formula. Generally, the glassier the body the more likely it is to warp. Uneven pots will warp more. Big pots tend to slump more.

[Diana Ferreira]

Inya, I am sorry - i spoke to her, she told me that it is on the firing schedule charts at every kiln at the studio, and I forgot to look. I will do that tomorrow morning first thing (at least we are a the same time day & night) and post from work.

[INYA]

Diana Ferreira, on 18 April 2012 - 06:15 PM, said:

Inya, I am sorry - i spoke to her, she told me that it is on the firing schedule charts at every kiln at the studio, and I forgot to look. I will do that tomorrow morning first thing (at least we are a the same time day & night) and post from work.

Thank you for having me in your mind...
I will fire on weekend

yep, the sun is just going down

[madi beattie]

hi, I fire my porcelain straight up to 1300 as it flattens out my pieces. I use paper clay sheets to cut my tiles and I have started placing the "off cuts" of the paper clay sheet around the edges of my porcelain tiles to flatten them while drying and it works very well. I don't have any experience of firing porcelain pots....sorry.

[INYA]

hey Diana,

have you maybe managed to check the firing out?

thanks...

[caki]

Hello

I also having trouble finding that good porcelain firing curve.

I have nearly the same program with the firing as INYA refers to, whith varied results....

Could someone pleas help me too with that firing curv?




Appreciate

[INYA]

1.
Diane Ferreira suggested (thay fire like that all the time):
this is all celsius, not F:
100 C/h until 200 C
200 C/h until 1250 C
hold 5 minutes

2.
I got another suggesstion:
120 C until 1190 C
65 C/h until 815 C (this is slow cooling)

3.
I do it mostly like that (and I got fairly good results but I have nontranslucent and quite stable body and thin and thick casts):
170 C/h until 1100
50 C/h until the end
hold 15 min

but there is nothing but trying