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Crystalline Malfunction

crystalline glaze L&LE23-T3

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#1 shayes

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Posted 24 October 2013 - 04:41 PM

After three successful crystalline firings with the same 4 glazes, my fourth crystalline firing failed with the exact same firing schedule. I had 14 pieces in the kiln and all of the glazes bubbled and flaked off except for one piece! Any advice on what happened? Why is the glaze matte, flaking off and no crystals? How could 13 of the 14 pieces fail?
 
The picture below is 2 vases with failed glaze and 1 vase with the successful glaze
The 3 vases were made with the same clay body, bisque fired at the same temperature and have the same glaze.


#2 mregecko

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Posted 24 October 2013 - 05:05 PM

Sorry to hear about this... We're probably going to need more information here to try and provide you with some help.

 

What type of crystalline glaze(s) were you using? Home-mixed or store-bought? Recipes (if home-mixed)?

Kiln type? Firing temperature and schedule?

Were these all fired in the same bisque firing? If so, have you had any other pieces from that same bisque firing that came out successfully?

 

When I hear bad crystal formation, flaking off, and matte glazes I immediately think that something went wrong with a firing schedule. But it's also possible if they were under-bisqued or had some sort of contaminant that got onto the bisque ware.



#3 Min

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Posted 24 October 2013 - 05:54 PM

I couldn't see a picture on your post...  Some crystalline glazes don't store well, they are usually mixed for immediate use and leftovers not kept, did you use stored glazes? Very frustrating isn't it when this type of thing comes along, it seems like you can just get something sorted out and then disaster strikes.

 

Min 



#4 Mark C.

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Posted 24 October 2013 - 10:51 PM

If all things are equal and 1 turned out what did you do different with this one?

This can be many things

a few are

glaze application is different?

placement in kiln is different?

pieces  where in areas that offgased or where subjected to offgassing different from surounding pots (this is subtle area to get to the bottom of)

The very nature of crystiline firing is hit and miss -at least it was back in my day.

I'm not assuming the auto control factor is always the same-they are controlled by thermocouple and they can change /go bad -whatever over time.

Where these pots sprayed or dipped or brushed asthat all can vary application.

And my last thought is if it was easy everyone could do it.This applies to most ceramics.

Post some more details on specifics

Mark


Mark Cortright
www.liscomhillpottery.com

#5 Wyndham

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Posted 25 October 2013 - 09:15 AM

If this was a new batch of glaze, could be several things like inverting amts

If it's the same glaze, screen it before applying as it can "clump up" as zinc does some strange stuff every now and then.

I've had problems if I use zinc that has not been calcined. Zinc shrinks a lot if not calcined.

if also sounds like you may have fired in a gas kiln and reduction will cause the exact results you described

Just a few things I've gone through as well.

Wyndham



#6 shayes

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Posted 25 October 2013 - 10:45 AM

I'm having trouble posting the picture.....I think its necessary for everyone to see. any suggestions? it says server failed

 

The firing was done in a brand new (only fired 20 times) L&L E23-T3 electric kiln. My programmed firing schedule is 4 segments:

1. 150 degrees F / hour to 250 degrees F. no hold

2. 300 degrees F / hour to 2200 degrees F. no hold

3. 108 degrees F / hour to 2345 degrees F. no hold

4. 325 degrees F / hour to 2000 degree F. hold for 4 hours

 

My last 3 firings with this schedule and the four chosen glazes have been successful.

Now my 4th firing with the same glazes has failed : All 4 of the glazes bubbled, turned matte and one glaze is now flaking off.

I used high fire b-mix with grog (same clay used in successful crystalline firings)

All 14 pieces were bisque fired at cone 08

the glaze was sprayed on thick

 

The thing that really blows my mind is that 1 out of 14 pieces was successful! and its actually one of the most beautiful crystalline results i've ever gotten!

That specific recipe I used on 7 pieces in that firing. 6 bubbled with no crystals and is matte, 1 crystallized and become glossy and smooth.

That recipe is Lithium carb .1%, zinc oxide (not calcined) 30%, fusion frit 75 (ferro 3110) 44.9%, silica 25%, bentonite 1%, nickel oxide 2%

 

In the kiln I had 2.5 layers of work, one of the shelves was placed close to the middle thermocouple....could this have effected the firing? but still how could one piece still be successful??

 

really appreciate all your support! I do not want to give up on crystalline, I think its worth all the struggle!



#7 shayes

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Posted 25 October 2013 - 11:26 AM

If this was a new batch of glaze, could be several things like inverting amts

If it's the same glaze, screen it before applying as it can "clump up" as zinc does some strange stuff every now and then.

I've had problems if I use zinc that has not been calcined. Zinc shrinks a lot if not calcined.

if also sounds like you may have fired in a gas kiln and reduction will cause the exact results you described

Just a few things I've gone through as well.

Wyndham

I used the same batch of glaze left over from a month ago. I mixed it well, but I will definitely try straining it again next time. Also the zinc was not calcined so I will try that as well too! the Firing was done in an L&L E23T-3 electric kiln. Thank you so much for the support!



#8 shayes

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Posted 25 October 2013 - 12:08 PM

Attached File  crystal.png   122.42KB   1 downloads



#9 Wyndham

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Posted 25 October 2013 - 03:10 PM

If the piece that turned out good was on the same level as the TC, then you may have a problem with the relays for the top and bottom. It looks like the middle got to temp but not the top or bottom or... another relay controled ring was out and the top/or bottom and the middle were firing .

In other words one or 2 of the relays maybe out.

The controller is looking at the middle and the top or bottom may be 100-200 deg off which would give this problem. Do you put cone packs on each level, you shoud as this will tell you were the issue could be.

Wyndham







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