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Please Help: What Causes Pinholes Etc In This Cone 6 Firing Set-Up?

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Hello!

 

Could anyone please give me hints on where to go next best to figure out where the following problem comes from?

 

Here are three examples of first tests made by me and my friend with glazes we found in recepy books and online, all for cone 6.

We are using an electric kiln at one workshop where we can only program a ramp with three steps and so we tried the following firing programme, while skipping the step 1 and the last one (so we had no hold on cooling and just had the kiln switch off after the 15min hold on the top temperature).

here the original firing programme: http://digitalfire.com/4sight/firingschedule/plainsman_cone_6_electric_standard_firing_schedule_114.html

 

I suspect we need a slower cooling. We can program the kiln to cool down with a constant temperature, but we can't add any hold into the programme. Any idea what would be a good temperature then?

 

We now also try to apply some of the glazes thinner.

 

Several texts I have read on the troubleshooting issues mention to lengthen the firing programme, but give no specifics about which step and how much to lengthen. Some say to use higher temperature, but doesn't give a hint in terms of how much higher etc.

 

Any advices would be highly appreciated!

Best wishes,

Martin

 

 

post-71183-0-10468400-1443183888_thumb.jpg

post-71183-0-96907000-1443183888_thumb.jpg

post-71183-0-64052600-1443183890_thumb.jpg

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Could you tell us about the clay body being used and your bisque firing temperature and schedule?  A clay that dark could be off-gassing during the glaze firing if not properly bisque fired.  Could you also post the glaze recipe so we can see what is in the glaze. 

 

Try adding a 10 minute soak/hold at the end of your firing -- if that does not work, then go to 15 minutes.  That should add enough heat to improve melting of the glaze.  But some of your problem may be glaze thickness (there some evidence of crawling) on test samples. 

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hello bciske! thank you for the fast reaction.

 

the schedule is as follows:

  166°C/hr to 945 300 1733 0 7:29     60°C/hr to 1190 108 2175 15min 11:50

then kiln off

 

the clay is this in the attached picture

 

unfortunately i don't know the specs of bisque since we work in a shared workshop :(

 

any idea whether it makes more sense to have the kiln cooling off with a fixed temperature (150F/Hr) and no hold (limitation of the kiln computer) than just switching it off? from what i have read it shall be better with a longer cooling, but most of the time people mention the hold in the cooling, which I can do, so I wonder whether the temperature for cooling shall be even lower to balance this a bit

 

thank you!

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just as a side note. in one of the texts i was looking at, they say that for pinhole troubleshoot, i could hold the temperature for maturing for up to 2hrs, does that mean the top temperature of 1190?

 

7. hold the kiln at the glaze maturing temperature for a soaking period of up to two hours

http://ceramicartsdaily.org/ceramic-glaze-recipes/glaze-chemistry-ceramic-glaze-recipes-2/how-to-correct-five-common-ceramic-glaze-defects/

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excuse me for butting in, but this looks like a cratering glaze.  a deliberate attempt to look exactly the way your picture is.  what is the recipe you found and what was the description that made you want to try it?

 

i made the mistake of trying some glaze recipes without knowing how they would turn out.  the ingredient list will tell one or all of the glaze experts here if that is what caused this. 

 

these are definitely not pinholes.

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hello. for example the first image shows this recipe:

 

https://www.flickr.com/photos/glazes/1085548412/in/album-72157602049172454/

 

WoDo 40/10 ^6-8 Ox. 

Recipe Name: WoDo 40/10
 
Cone: 6-8 Color:
Firing: Surface: Matte
 
Amount Ingredient
40 Nepheline Syenite
10 Talc
6 Wollastonite
25 Dolomite
20 Ball Clay--Old Mine #4
101 Total

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Your best bet for the firing is to use cones in the kiln, so you know exactly how much heat work you're getting. Changing the firing schedule, application and clay body all at the same time won't tell you anything. Only change one variable at a time. Start with the clay body. Test the glaze with the same firing schedule on a white or lighter color body, and put cones in the kiln.

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unfortunately i don't know the specs of bisque since we work in a shared workshop

Am I right in thinking that putting the clay through the bisque twice would

reduce any subsequent out-gassing in the glaze firing?

 

... at least as a test.

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excuse me for butting in, but this looks like a cratering glaze.  a deliberate attempt to look exactly the way your picture is.  what is the recipe you found and what was the description that made you want to try it?

 

i made the mistake of trying some glaze recipes without knowing how they would turn out.  the ingredient list will tell one or all of the glaze experts here if that is what caused this. 

 

these are definitely not pinholes.

This glaze doesn't come close to cone 6 limits and probably is boiling, hence the cratering.  Try it on a pot you are bisquing and see what happens, in other words it is like a cone 04 glaze with the amount of flux it has.

David

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excuse me for butting in, but this looks like a cratering glaze.  a deliberate attempt to look exactly the way your picture is.  what is the recipe you found and what was the description that made you want to try it?

 

i made the mistake of trying some glaze recipes without knowing how they would turn out.  the ingredient list will tell one or all of the glaze experts here if that is what caused this. 

 

these are definitely not pinholes.

This glaze doesn't come close to cone 6 limits and probably is boiling, hence the cratering.  Try it on a pot you are bisquing and see what happens, in other words it is like a cone 04 glaze with the amount of flux it has.

David

 

 

Hello David, thank you for the comment. I will give that test you mention a try if they allow me where we are firing. Strange than, that the author writes it's for cone 6 to 8

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excuse me for butting in, but this looks like a cratering glaze.  a deliberate attempt to look exactly the way your picture is.  what is the recipe you found and what was the description that made you want to try it?

 

i made the mistake of trying some glaze recipes without knowing how they would turn out.  the ingredient list will tell one or all of the glaze experts here if that is what caused this. 

 

these are definitely not pinholes.

This glaze doesn't come close to cone 6 limits and probably is boiling, hence the cratering.  Try it on a pot you are bisquing and see what happens, in other words it is like a cone 04 glaze with the amount of flux it has.

David

 

 

Hello David, thank you for the comment. I will give that test you mention a try if they allow me where we are firing. Strange than, that the author writes it's for cone 6 to 8

 

I am going to do a bisque firing shortly so I will try the glaze at cone 06 and let you know what happens.  If you are looking for a satin matte that covers the range of cone 6 to 8 than you could try this one:

Ferro frit 3134      12.1

Custer feldspar      5.7

EPK clay               40.4

Talc                      14.1

Wollastonite          20

Silica                      7.7

Total                    100

David

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Dear David, thank you for the recipe! Would you happen to have a picture of it?

As soon as I can get my son to figure out how to post a picture, I will send one. Actually I was able to post 2 images of this satin glaze in the gallery.

David

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Hello!

 

Could anyone please give me hints on where to go next best to figure out where the following problem comes from?

 

Here are three examples of first tests made by me and my friend with glazes we found in recepy books and online, all for cone 6.

We are using an electric kiln at one workshop where we can only program a ramp with three steps and so we tried the following firing programme, while skipping the step 1 and the last one (so we had no hold on cooling and just had the kiln switch off after the 15min hold on the top temperature).

here the original firing programme: http://digitalfire.com/4sight/firingschedule/plainsman_cone_6_electric_standard_firing_schedule_114.html

 

I suspect we need a slower cooling. We can program the kiln to cool down with a constant temperature, but we can't add any hold into the programme. Any idea what would be a good temperature then?

 

We now also try to apply some of the glazes thinner.

 

Several texts I have read on the troubleshooting issues mention to lengthen the firing programme, but give no specifics about which step and how much to lengthen. Some say to use higher temperature, but doesn't give a hint in terms of how much higher etc.

 

Any advices would be highly appreciated!

Best wishes,

Martin

If you skipped step1, this meant the kiln went as fast as it can to step 2.  That would not be a good idea as the kiln could have been going at 500 deg per hour or more  and anything could have happened to the glaze as it tried to adhere to the pot.  I am wrong as to what I said about this glaze.  It does have a lot of flux and doesn't fit in cone 6 limits.  I fired it using EPK instead of OM4 ball clay to cone 06, it was a very dry white surface no blemishes, than fired to cone 4 still a dry white surface, then to cone 6 still white but not quite as dry a surface, cone 8 still dry off white matte.  Please post the firing schedule used.

David

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Hello!

 

Could anyone please give me hints on where to go next best to figure out where the following problem comes from?

 

Here are three examples of first tests made by me and my friend with glazes we found in recepy books and online, all for cone 6.

We are using an electric kiln at one workshop where we can only program a ramp with three steps and so we tried the following firing programme, while skipping the step 1 and the last one (so we had no hold on cooling and just had the kiln switch off after the 15min hold on the top temperature).

here the original firing programme: http://digitalfire.com/4sight/firingschedule/plainsman_cone_6_electric_standard_firing_schedule_114.html

 

I suspect we need a slower cooling. We can program the kiln to cool down with a constant temperature, but we can't add any hold into the programme. Any idea what would be a good temperature then?

 

We now also try to apply some of the glazes thinner.

 

Several texts I have read on the troubleshooting issues mention to lengthen the firing programme, but give no specifics about which step and how much to lengthen. Some say to use higher temperature, but doesn't give a hint in terms of how much higher etc.

 

Any advices would be highly appreciated!

Best wishes,

Martin

If you skipped step1, this meant the kiln went as fast as it can to step 2.  That would not be a good idea as the kiln could have been going at 500 deg per hour or more  and anything could have happened to the glaze as it tried to adhere to the pot.  I am wrong as to what I said about this glaze.  It does have a lot of flux and doesn't fit in cone 6 limits.  I fired it using EPK instead of OM4 ball clay to cone 06, it was a very dry white surface no blemishes, than fired to cone 4 still a dry white surface, then to cone 6 still white but not quite as dry a surface, cone 8 still dry off white matte.  Please post the firing schedule used.

David

 

 

Hello David,

 

the 1st step in our schedule is identical with the second one in the linked schedule, so we start from 0 and go with 166°C/hr to 945... Do you think that's too fast then? I'm sure it won't take too much more energy if we drop it slower, but again, it's a wild guess for me in terms of how much to drop it.

 

Thank you!

M

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