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Underglaze And Clear Glaze Chipped Off! Low Fire


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#1 Panamax

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Posted 27 April 2011 - 02:33 PM

I made a plaster mold of a piece and cast it in a low fire white pouring slip. The pieces were handpainted using Amaco Velvets in the greenware stage. Fired to cone 05, applied a clear glaze and fired to cone 05 for the glaze firing. I made four pieces. Three turned out without any issues. The one had some parts of the paint flake off when I picked it up. I have never had this happened to me and have worked with molds and casting. Any suggestions as to what happened and why only the one had some areas that flaked off? Thanks in advance for any advise!Attached File  101.JPG   2.85MB   27 downloads



#2 Chris Campbell

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Posted 28 April 2011 - 09:14 AM

Is it possible it was the first piece you cast and the surface picked up some ? off the mold?

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#3 Panamax

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Posted 28 April 2011 - 09:38 PM

Is it possible it was the first piece you cast and the surface picked up some ? off the mold?



#4 Panamax

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Posted 28 April 2011 - 09:42 PM

It could be one of the first ones, now that you mention it. But what does the plaster do to the casting slip? Create some kind of barrier to prevent the underglaze from adhering? Interesting.

#5 Lucille Oka

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Posted 29 April 2011 - 08:43 AM

I made a plaster mold of a piece and cast it in a low fire white pouring slip. The pieces were handpainted using Amaco Velvets in the greenware stage. Fired to cone 05, applied a clear glaze and fired to cone 05 for the glaze firing. I made four pieces. Three turned out without any issues. The one had some parts of the paint flake off when I picked it up. I have never had this happened to me and have worked with molds and casting. Any suggestions as to what happened and why only the one had some areas that flaked off? Thanks in advance for any advise!Attached File  101.JPG   2.85MB   27 downloads




I don’t recall this ever happening to my ware in 36 years of potting until I had to have some ware ‘emergency’ fired for a show. It never occurred to me that the potters in that studio would pick up ware with oily hands. I always assume that studio rules prevail. The ‘Do Not touch other people’s work’ is always the first on any studio rules list. On the day that I came to pick up my ware I saw that people were allowed to eat in the studio! On the clay forming tables! Near the wheels and near the glazing areas Yikes!! It is so very easy to transmit oils by eating in the studio.

I am sure it was neither the underglazes nor glaze that I used that caused this problem. Only one piece out of 38 had this flaking and on a rim.
Trying to figure out what happened poses a lot of questions. You can use these questions as a diagnostic.

-Was the piece handled by anyone who could have placed natural body oils from their hands or even sweat from their face on the piece? Oils create a resist and affect glaze adherence.
-Did anyone possibly splatter some food, oil or oily liquid or wax on the piece?

Some of the areas on your image looked as if drops had been falling down at an angle.

-Was the piece bisque fired and rinsed prior to glazing with unclean hands?

-Was it possible that some critter walked or flew by and 'stopped' on the piece?
They have oils also.
There are a lot of variables but all we can really do is try to limit contact to our ware and be as clean as we can. Tell family and friends to be extra careful and Do Not touch the ware before it is glaze fired. Keep your ware covered in plastic until ready to be glazed and/or fired.
John 3:16
"For God so loved the world that He gave His only begotten Son, that whosoever believeth in Him should not perish but have everlasting life".

#6 Panamax

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Posted 04 May 2011 - 01:12 PM


I made a plaster mold of a piece and cast it in a low fire white pouring slip. The pieces were handpainted using Amaco Velvets in the greenware stage. Fired to cone 05, applied a clear glaze and fired to cone 05 for the glaze firing. I made four pieces. Three turned out without any issues. The one had some parts of the paint flake off when I picked it up. I have never had this happened to me and have worked with molds and casting. Any suggestions as to what happened and why only the one had some areas that flaked off? Thanks in advance for any advise!Attached File  101.JPG   2.85MB   27 downloads




I don’t recall this ever happening to my ware in 36 years of potting until I had to have some ware ‘emergency’ fired for a show. It never occurred to me that the potters in that studio would pick up ware with oily hands. I always assume that studio rules prevail. The ‘Do Not touch other people’s work’ is always the first on any studio rules list. On the day that I came to pick up my ware I saw that people were allowed to eat in the studio! On the clay forming tables! Near the wheels and near the glazing areas Yikes!! It is so very easy to transmit oils by eating in the studio.

I am sure it was neither the underglazes nor glaze that I used that caused this problem. Only one piece out of 38 had this flaking and on a rim.
Trying to figure out what happened poses a lot of questions. You can use these questions as a diagnostic.

-Was the piece handled by anyone who could have placed natural body oils from their hands or even sweat from their face on the piece? Oils create a resist and affect glaze adherence.
-Did anyone possibly splatter some food, oil or oily liquid or wax on the piece?

Some of the areas on your image looked as if drops had been falling down at an angle.

-Was the piece bisque fired and rinsed prior to glazing with unclean hands?

-Was it possible that some critter walked or flew by and 'stopped' on the piece?
They have oils also.
There are a lot of variables but all we can really do is try to limit contact to our ware and be as clean as we can. Tell family and friends to be extra careful and Do Not touch the ware before it is glaze fired. Keep your ware covered in plastic until ready to be glazed and/or fired.


Thank you! This is possibly what happened. I will be extra careful next time. As with everything, complacency got me.




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