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#1 TypicalGirl

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Posted 02 April 2010 - 03:20 PM

I am having an issue with a glaze I want to work with so I thought I might find some input here.

The problem is that the glaze falls off the ware when it dries.
Doesn't matter if its applied to bone dry greenware or bisqued ware.
Typically I'm pouring it on, fairly thickly - usually 2 coats.

After its completely dry (and somewhat chalkier than the other glazes I use), it starts falling off.
I don't seem to have that issue if I apply it over another glaze, just when its on its own.
Glaze is as follows:

Haynes White

Neph Sy 45
Silica 30
Whiting 8
Dolomite 10
Talc 7


Last batch I made (thought perhaps I had something wrong the first time) I added 3% bentonite, thinking that might help it stay on the ware a little better, but it didn't seem to help.
Cathi Newlin, Angels Camp, Ca
box49@caltel.com
http://www.CNewlin.com

#2 Autumn

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Posted 02 April 2010 - 10:14 PM

Hi,

There isn't any clay in the glaze to help adhere it and the other materials are pretty flaky. What cone and what surface are you expecting from this? Maybe some adjustments could be made by reducing the neph sy and adding some clay - but not sure how it would affect your final surface and the melt.

Autumn

#3 Matt Katz

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Posted 05 April 2010 - 11:44 AM

Hi,

There isn't any clay in the glaze to help adhere it and the other materials are pretty flaky. What cone and what surface are you expecting from this? Maybe some adjustments could be made by reducing the neph sy and adding some clay - but not sure how it would affect your final surface and the melt.

Autumn


Agreed, Clay in a glaze formula aids in application and glaze suspension.

An alternative may be CMC, for application.

#4 maryg

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Posted 14 April 2010 - 09:40 AM

I am having an issue with a glaze I want to work with so I thought I might find some input here.

The problem is that the glaze falls off the ware when it dries.
Doesn't matter if its applied to bone dry greenware or bisqued ware.
Typically I'm pouring it on, fairly thickly - usually 2 coats.

After its completely dry (and somewhat chalkier than the other glazes I use), it starts falling off.
I don't seem to have that issue if I apply it over another glaze, just when its on its own.
Glaze is as follows:

Haynes White

Neph Sy 45
Silica 30
Whiting 8
Dolomite 10
Talc 7


Last batch I made (thought perhaps I had something wrong the first time) I added 3% bentonite, thinking that might help it stay on the ware a little better, but it didn't seem to help.



#5 John Britt

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Posted 14 April 2010 - 09:56 AM

If CMC and bentonite additions don't help ...then I would ask if you have added Epsom salts.

What sometimes happens, is that people add a flocculant (or the glaze self-flocculates) and then the glaze becomes too thick. They then add water and this cause too much shrinkage and the glaze flakes off the pot. (the caveat is that normally the Nepheline Syenite in this glaze should cause it to deflocculate but I don't know about your water, whether it is hard, soft, well, city, etc. Or the interaction of dolomite and talc, etc.) All I know is that I have seen this happen, and specifically with kakis (tomato reds). Something in them, over time, causes them to flocculate and then people add water and they flake off. The following solution has helped.

So, since I am not there, I would take a cup of the glaze out and add a drop or two or three of a deflocculant (like sodium silicate or darvan 7, darvan 811) and then when it visibly thins out, try to apply it on a cup. See if it flakes off. If that works, then it has too much water and what you may need to do is to deflocculate the whole glaze bucket and then allow the water to evaporate (since it contains soluble materials you don't want to pour any off!) or add some more dry glaze to make it the right consistency.

This is hard to diagnose from email. There always seems to be some unknown thing the is not revealed.

I would appreciate it if you would let me know if this works, johnbrittpottery@gmail.com

John Britt
www.johnbrittpottery.com
Thanks,

John Britt
www.johnbrittpottery.com
http://ncclayclub.blogspot.com

#6 Kathy Fields

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Posted 20 April 2010 - 09:04 PM

Not sure if my quick post uploaded, so I'll re-post. Please forgive me if there's a duplication.

Glad you asked the question as I've had similar experiences with a commercial glaze from Coyote (NM glaz/clay company). Most often I layer glazes, so have a fair experience with any glaze used more than once.

So, when I decorated with Croc Blue over Red Gold on a platter, the blue flaking off was a surprise. I blew off all roughed up bottom glaze, but no difference. Fired as usual to see what would happen. The major differece is that the combining colors are muted, when past experience has seen bright/shiny.

Two pieces are attached: one is the platter and the other shows the more normal result when using this combination. Firing was electric, ^6, with normal cool down. Same process for both pieces

All suggestions/ideas/ teaching areAttached File  IMG_0430.JPG   26.91KB   47 downloadsAttached File  IMG_7301.JPG   41.66KB   48 downloads welcome.

#7 Les

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Posted 05 July 2010 - 09:58 AM

I am having an issue with a glaze I want to work with so I thought I might find some input here.

The problem is that the glaze falls off the ware when it dries.
Doesn't matter if its applied to bone dry greenware or bisqued ware.
Typically I'm pouring it on, fairly thickly - usually 2 coats.

After its completely dry (and somewhat chalkier than the other glazes I use), it starts falling off.
I don't seem to have that issue if I apply it over another glaze, just when its on its own.
Glaze is as follows:

Haynes White

Neph Sy 45
Silica 30
Whiting 8
Dolomite 10
Talc 7


Last batch I made (thought perhaps I had something wrong the first time) I added 3% bentonite, thinking that might help it stay on the ware a little better, but it didn't seem to help.



#8 Les

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Posted 05 July 2010 - 10:09 AM

I've had this problem a few times, and remember reading a solution that seems simple but effective. I't doesn't involve glaze chemistry, kiln firing temps, etc.

Here it is: Do not apply a thick coat of glaze all at once. If you're either dipping or brushing, apply a normal coat, and let it dry completely, in most cases 24 hours. Then you are ready to dip or brush the second coat, to add to the thickness of the glaze. Also, to insure the at the first coat bonds well, a fast dip in water to dampen (not wet) the bisque will help suck in and bond that first coat, but then let it dry 24 hours before the second coat is applied. This shoulod minimize flacking

#9 Marcia Selsor

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Posted 17 July 2010 - 06:28 AM

I think you need to check the source of this glaze. It doesn't add up. As the previous post mentioned, there is no clay (Kaolin or Ball clay) for it to adhere.

#10 bciskepottery

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Posted 17 July 2010 - 12:33 PM

I think you need to check the source of this glaze. It doesn't add up. As the previous post mentioned, there is no clay (Kaolin or Ball clay) for it to adhere.



The recipe is consistent with that for Haynes White in John Britt's book, The Complete Guide to Hire Fire Glazes, pg. 63. The problem may be more in glaze application -- two thick coats by pouring (not sure why two thick coats are needed). Two thick coats may be more water than the bisque can absorb. May want to try a single application and see if the glaze falls off. Also, is the glaze the right consistency? May also want to consider the bisque temperature for the particular clay body being used.




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