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Refring?

Worn heatvitrification

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#1 Biglou13

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Posted 22 July 2014 - 07:26 PM

I plan on testing....

Keeping in mind work heat.

When a piece gets refired, does it become more mature? Does absorption level decrease, does a glaze become more "glassy"

I'm sure there is a difference if you doubled the time at final temp. But as a refire you just doubled the time at fired temp.

I've seen subtle differences in glaze. But never thought about the body.

Is there risk of over firing/ slumping if my body is close to limit?

I'll run tests.....
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#2 Marcia Selsor

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Posted 22 July 2014 - 08:37 PM

See PC question of the week
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#3 Mark C.

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Posted 22 July 2014 - 10:09 PM

The glazes get more runny and the body gets more abuse-refire a pot 5 times and see how brittle it is.

I have never had the body improve and my refire to keepers is about 50%

I do like salt pots refired in reduction kiln it really makes them spectacular.

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#4 Min

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Posted 22 July 2014 - 10:22 PM

Firing to a lower cone sometimes avoids the bloats or slumping. 

 

A lot of people refire iron reds to bisque temp to get a redder red if they can't slow cool their kiln, no problem with bloating or slumping there.

 

I believe porosity can actually go up with some clay bodies if they are way over fired.



#5 synj00

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Posted 23 July 2014 - 02:35 PM

Great info and question Biglou13! I've refired several of my earlier vessels without any visible defects. These were not largve vessels but pinch pots that were farily thick and using heavily grogged raku clay as well. I notice that the glaze does not adhere as everyone who's ever done it can attest to. Not much help but its my limited perspective. Love the learning I get here! Something to watch out for.

 

Another question. If you refire to your glazes maturation point could this repair pinholes without affecting the look of the piece to much? I suppose it would depend on how runny a glaze is?


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#6 Min

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Posted 23 July 2014 - 05:28 PM

Another question. If you refire to your glazes maturation point could this repair pinholes without affecting the look of the piece to much? I suppose it would depend on how runny a glaze is?

 

I hate pinholes, they turn up in all the wrong places don't they? Yup, refiring can smooth over pinholes but not always. You can rub a tiny bit of dry glaze into the pins and refire. I would put those pots in the coolest area of your kiln if possible. Yes, most glazes do move more on subsequent firings to similar cones. Sometimes they look better, sometimes not so much.

 

Couple other thoughts about pinholes if they are a real problem, apologies if you already know this stuff.

 

- clean bisque firing to around 05 - 04 with good ventilation, avoid stacking pots inside each other

 

- sub out any ingredients that have a high loi rate, for example if your glaze has a large amount of whiting it helps to reformulate glaze to use wollastonite in place of it (and some of the silica). Talc and dolomite have high loi rates also. Can't always get rid of them but helps if you can swap for something else like frit 3249 to supply the magnesium for example.

 

- glazes with high viscosity take longer to heal over the pins. Longer soak at the top temp without over firing sometimes helps.



#7 synj00

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Posted 24 July 2014 - 11:32 AM

Min,

 

Yes they turn up in the worst places! No apologies necessary. It always helps to get information even if already known in a different format, if you know what I mean. Explanations differ from person to person and sometimes they stick better when its explained differently. I didn't know about the glaze inside the pinholes. I have tried longer soak period but still get them. I dont make my own glazes yet but with the pinhole problems I'm getting more and more inclined to start mixing my own to get the control I need. I have been told on several occasions that a longer cooling period might help as well. I need to get with my kiln manual and instead of firing up slow, start fast and do a long controlled cooling. 


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#8 synj00

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Posted 24 July 2014 - 11:33 AM

Sorry Biglou13, not trying to hijack the thread!


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#9 Min

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Posted 24 July 2014 - 02:26 PM

Sorry Biglou13, not trying to hijack the thread!

 

Me too Lou!

 

One more thing re pinholes and downfiring. I have started trying a 30 min soak at 125F below top firing temp to see what it does with pinholes. I have one glaze that has a lot of titanium dioxide in it that is prone to pinholes. Haven't done enough testing to have a definitive conclusion but I think it does help a bit. This is a glossy glaze that goes matte if I slow cool it but the new way I'm testing avoids this. It doesn't seem to add a lot of heatwork but it does add some.



#10 Biglou13

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Posted 24 July 2014 - 08:54 PM

Hi jack away please.
Any discussion is good learning.
No apologies necessary

I'm doing a 30 min hold but lowered top temp. Took some testing. But this is not for super glossy glazes.

True most glossy glazes want to crash cool.

I don't have issues with pinholes yet.

My query was more on theoretical side. What's the difference with 2x firing vs 60 minute hold at temp. I think the later would have over firing issues. But why doesn't refire.


While none of my pieces have slumped. I have 3 x 4 x. Fired some pieces.

I had to re fire some black glossy pieces from my "special" schedule. Went to 6 ish on second firing I got the most amazing results. With iridescence in black
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#11 Biglou13

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Posted 24 July 2014 - 09:43 PM

Re pin holing do you rinse your pieces before glaze?
Caution big brother is watching.
The beige is blinding!!!!!!
The middle of the road is boring

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