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Small bubbles in glazed bowls


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13 hours ago, Min said:

This plus finding a cooler firing produced more blisters is a good indicator that the glaze likely isn't overfired. If you had gotten more blisters or they didn't get better then I would say it was over fired.

One thing that jumps right out at me is the colour of that dark green glaze. It's very pretty but I'm a bit concerned that it probably contains enough copper to leach out. Have you tried doing a lemon slice (or vinegar) leach test? Are you getting the most blisters with the dark green glaze? Is the light green from the same line of glazes?

Have you tried a drop and hold with the glaze? This could help both the pinholes and the blisters. There isn't a one size fits all drop and hold schedule, what you are aiming to do is find the temperature where the glaze is still fluid enough to soak the kiln at to allow the blisters time enough to heal over. For me that temperature is 38C below the peak temperature and I soak for approx 20 minutes. This does add a bit of heatwork but not much.

What is your bisque schedule? Is your bisque firing vented well? Do you heavily load the bisque and stack bowls inside of bowls?

Glaze blisters can be one of the most frustrating things to figure out because there can be so many causes. Adding to that is we don't know the recipe for the glaze you buy so we can't look at the chemistry side of things insofar as loss on ignition, alumina levels, high viscosity fluxes etc.

@MinThank you for your input.

"This plus finding a cooler firing produced more blisters is a good indicator that the glaze likely isn't overfired. If you had gotten more blisters or they didn't get better then I would say it was over fired." I understand the first sentence here on its own, but I don't understand it in realtionship to the 2nd. In the second sentence are you refering to the re firing to fix the bubbles?

I'll bring a lemon to the studio today. I sometimes get blisters with other glazes but rarely and maybe one or two. Not 5-10. The problem is mostly with the green. The light green you see in the photo is the same glaze but just a thinner application. 

I have a Cromartie kiln with a safefire 3000 series. I bought it used and it didn't come with a manual. I have collected several manuals from related controllers but not the exact one that I have.  The illustration on my controller shows "a linked program" but I haven't figured out how to link because my controller doesn't "react" the way the manual says it should when I press the "secret button" under the logo. "Lock" flashes on the screen instead of  Ln 00 (for link) so I'm a little scared... I don't want to lock myself out of the controller when I have so much firing to do the next couple weeks. So right now I only have the possibility of ramp 1, set temp 1, ramp 2, set temp 2, a soak, and a slow cool...unless maybe if I manually start another program right after my glaze program...I'll see if I can set a 2nd program for function that way using the  38C below the peak temperature and I soak for approx 20 minutes that you use. I'm not sure when I'll actually be able to test fire this way though due to needing to fire student work.

My bisque schedule is 100 C per hour to 930 and then 25 C per hour to 1037 C. Although the temp readings don't correspond to the Orton cone chart, I know this fires to cone 04 because I regularly check it with cones. There is no venting really, in other words no forced air flow and I don't have a hood. I do have a powerful vent fan in the room. And I fire when I am not in the studio. There are like "vent slats" in the top of the kiln. I can take a picture later. I considered buying one of those under mounted fans, but that would require drilling into my kin which scares me a bit.... and the instructions for that say that you are supposed to cover any other vents and I don't know how I could do that with the vent slats...

I do still get blisters without stacking during the bisque but as I said never quite like this last disaster :).  When I bisqued the large bowl, I had a footed bowl sitting inside, so the surfaces of the two bowls were not right up against each other, but then I also had a plate on top of that... not sure how much that would have blocked heat and air movement. When I go to the studio today, I will restack those pieces to try to get an idea of that, and I'll let you know. 

So I'm curious and would love to confirm...pin holes are caused by gasses escaping from the clay... like from organic materials that haven't fully burnt off? Or if they clay gets too hot and starts to break down (website lists my clays top temp at 1280 C, so that shouldn't be the problem here)? And bubbles or blisters could be from gasses escaping from the clay? glazes breaking down because they've gotten too hot? Or they can be part of the melting process and can just be healed with the right schedule? Or there can also be more causes for all of these things that are beyond my knowledge level...

Thanks again!

 

Safefire 3000.png

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38 minutes ago, feistyfieryceramics said:

I have a Cromartie kiln with a safefire 3000 series. I bought it used and it didn't come with a manual. I have collected several manuals from related controllers but not the exact one that I have.  The illustration on my controller shows "a linked program" but I haven't figured out how to link because my controller doesn't "react" the way the manual says it should when I press the "secret button" under the logo. "Lock" flashes on the screen instead of  Ln 00 (for link) so I'm a little scared... I don't want to lock myself out of the controller when I have so much firing to do the next couple weeks. So right now I only have the possibility of ramp 1, set temp 1, ramp 2, set temp 2, a soak, and a slow cool...unless maybe if I manually start another program right after my glaze program...I'll see if I can set a 2nd program for function that way using the  38C below the peak temperature and I soak for approx 20 minutes that you use. I'm not sure when I'll actually be able to test fire this way though due to needing to fire student work.

If it's any help  ...

The first entry dated October 18, 2018 in this thread contains.

LINKING (Not applicable to SP and MP models) At the point of the program entry where ‘End’ is displayed, you may link to another program if a more complex firing cycle is required. Whilst ‘End’ is displayed in program entry press and hold the secret key under the ‘P’ of IPCO. The ↑ / ↓ keys allow a Ln number to be displayed. When the program is run this link number will direct the controller to continue firing with the values in the ‘linked’ program. You may make as many links as you wish, however, each link uses up one of your ten programs which are thus not available to be run independently. Also be very careful that you do not link back to a program which is earlier in your current firing cycle, or a continuous loop will result.

The second entry dated October 18, 2018 is from somebody who managed to get a copy for his series 2 model from https://tinyurl.com/9ykkx55s

 

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4 hours ago, feistyfieryceramics said:

The problem is mostly with the green. The light green you see in the photo is the same glaze but just a thinner application. 

If the glaze is thick enough with the pale green then the blisters could very well be from too thick a glaze layer. It's going to be harder for the blisters to heal over with a thick glaze layer. If the glaze is viscous and thick it's going to take longer for the blisters (and pinholes) to heal over. Drop and hold might work to smooth things out.

4 hours ago, feistyfieryceramics said:

I'll bring a lemon to the studio today.

Slice of lemon, place it on the glaze then cover it with plastic wrap so it doesn't dry out. Leave it sit for a couple days then wash and dry the area and look for a colour or sheen difference.

4 hours ago, feistyfieryceramics said:

So I'm curious and would love to confirm...pin holes are caused by gasses escaping from the clay... like from organic materials that haven't fully burnt off? Or if they clay gets too hot and starts to break down (website lists my clays top temp at 1280 C, so that shouldn't be the problem here)? And bubbles or blisters could be from gasses escaping from the clay? glazes breaking down because they've gotten too hot? Or they can be part of the melting process and can just be healed with the right schedule? Or there can also be more causes for all of these things...

There are a lot of reasons for blisters, good article here on causes. Basically they can be from the bisque firing, glaze firing, glaze or clay or a combination of these things so all of what you wrote and then some.

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what @Min said.  I have to be honest, after trying and trying to sort out a blistering issue with a glaze, I finally gave up on that glaze.  I could not depend on it and I was just frustrated with always having to deal with it.  Never knowing if my pots would be great or problematic.  So I walked away from that glaze.  I still have it in a bucket and I am tempted to just try it again.  But then if I get one bowl/mug/plate that turns out, it will encourage me to use it more often and then I start the whole dang cycle again!! 

r.

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On 6/20/2021 at 3:05 AM, feistyfieryceramics said:

with the glaze rated for 1260C according to the store where I buy the powdered glaze to mix

 

46 minutes ago, Callie Beller Diesel said:

We never did get the recipe for this glaze, which could also help us troubleshoot. If it’s a little underfired, maybe it’s unbalanced in some way. Let’s have a look!

psst, purchased dry glaze.

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On 6/28/2021 at 1:57 PM, PeterH said:

If it's any help  ...

The first entry dated October 18, 2018 in this thread contains.

LINKING (Not applicable to SP and MP models) At the point of the program entry where ‘End’ is displayed, you may link to another program if a more complex firing cycle is required. Whilst ‘End’ is displayed in program entry press and hold the secret key under the ‘P’ of IPCO. The ↑ / ↓ keys allow a Ln number to be displayed. When the program is run this link number will direct the controller to continue firing with the values in the ‘linked’ program. You may make as many links as you wish, however, each link uses up one of your ten programs which are thus not available to be run independently. Also be very careful that you do not link back to a program which is earlier in your current firing cycle, or a continuous loop will result.

The second entry dated October 18, 2018 is from somebody who managed to get a copy for his series 2 model from https://tinyurl.com/9ykkx55s

 

@PeterH Thanks! I found that post too and actually contacted the guy who originally posed it. He sent me the manual he has which is similar but different from the one that Cromartie emailed me previously. I found the secret button and tried pressing it when the screen says "lock"... and in another manual I have for a similar controller, it says to hold the secret button and hit the up and down keys to set a lock code...so I'm nervous about accidentally locking my kiln! So I'll experiment with it more once all my students work is fired and then I hope I can link programs and try this drop and hold! Thanks!

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On 6/28/2021 at 5:30 PM, Min said:

If the glaze is thick enough with the pale green then the blisters could very well be from too thick a glaze layer. It's going to be harder for the blisters to heal over with a thick glaze layer. If the glaze is viscous and thick it's going to take longer for the blisters (and pinholes) to heal over. Drop and hold might work to smooth things out.

Slice of lemon, place it on the glaze then cover it with plastic wrap so it doesn't dry out. Leave it sit for a couple days then wash and dry the area and look for a colour or sheen difference.

There are a lot of reasons for blisters, good article here on causes. Basically they can be from the bisque firing, glaze firing, glaze or clay or a combination of these things so all of what you wrote and then some.

@Min Thank you! This is great info! I have started by test.

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On 6/28/2021 at 6:15 PM, Roberta12 said:

what @Min said.  I have to be honest, after trying and trying to sort out a blistering issue with a glaze, I finally gave up on that glaze.  I could not depend on it and I was just frustrated with always having to deal with it.  Never knowing if my pots would be great or problematic.  So I walked away from that glaze.  I still have it in a bucket and I am tempted to just try it again.  But then if I get one bowl/mug/plate that turns out, it will encourage me to use it more often and then I start the whole dang cycle again!! 

r.

@Roberta12 Sadly, I may end up doing the same. 

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On 6/28/2021 at 7:03 PM, Callie Beller Diesel said:

We never did get the recipe for this glaze, which could also help us troubleshoot. If it’s a little underfired, maybe it’s unbalanced in some way. Let’s have a look!

@Callie Beller Diesel unfortunately I buy it from this place https://seemann.nu/ the make the recipe while your waiting and then you mix it at home. I doubt they'd be willing to share the recipe with me. Also starting tomorrow they're on vacation for a whole month!

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Also thank you all for your warnings about commissions and intolerance for BS from clients! I've been going on good faith since these people who have asked me to make things for them are neighbors or family of neighbors but now I understand that if I am going to continue making things on request, I need to get at least a damn deposit before I get started!

The guy who I made the big bowl for didn't respond to my most recent email and then didn't come on the date I expected him to for his mugs and small bowl, and his plate sample. Another person who asked for 4 of my mugs but a bit smaller, messaged me a week later (after I had already made them all) and said she changed her mind because she decided the rim would be too thick for cappuccino. The mugs she had liked were intentionally "chewy" and of course if I had known she wanted a thinner rim (and therefore not just a "smaller version" of the chewy mugs) I could have done that no problem! So I'm feeling pretty frustrated. But you have inspired me now to seriously deprioritized this big bowl. I made two more big ones on the day I saw the glaze was a disaster, I'll trim them, I'll finish firing my students work, and them I'm out of here for the summer. I've been trying to get to my family for 1.5 years and I'm not going to wait any longer for a person who doesn't respond to emails or show up. I'll do more testing and then finish the bowls when I get back if he finally gets back to me and still wants it. mic drop ;)

Back to the detective work... I'm also wondering if it is possible to more thoroughly bisque without going up a cone? If I make something bigger and thicker than I usually do (like this big bowl), how should I change the firing schedule to make sure it's getting as much heat work as my cones?

Thanks!

 

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I just sent two small mugs to Colorado -I had to send photos twice and it took 7 emails (not done yet)and she does not like them and is returning them. I offered a full refund

I do not like mail order and am at the end of my rope right now with her. She tuerns on the computer a few times a week so its really slwo communication -her Friend has my work.

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10 minutes ago, Mark C. said:

I just sent two small mugs to Colorado -I had to send photos twice and it took 7 emails (not done yet)and she does not like them and is returning them. I offered a full refund

I do not like mail order and am at the end of my rope right now with her. She tuerns on the computer a few times a week so its really slwo communication -her Friend has my work.

Tell me where she lives, I will take care of this for you!!!  Your mugs are da Bomb!

r.

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10 hours ago, Mark C. said:

I just sent two small mugs to Colorado -I had to send photos twice and it took 7 emails (not done yet)and she does not like them and is returning them. I offered a full refund

I do not like mail order and am at the end of my rope right now with her. She tuerns on the computer a few times a week so its really slwo communication -her Friend has my work.

Sugest she gijvs them to her friend for bday, Xmas,4th July celeb.!!! Save everyone the bother.

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16 hours ago, Mark C. said:

I just sent two small mugs to Colorado -I had to send photos twice and it took 7 emails (not done yet)and she does not like them and is returning them. I offered a full refund

I do not like mail order and am at the end of my rope right now with her. She tuerns on the computer a few times a week so its really slwo communication -her Friend has my work.

That sound horrible! In my very little experience, it already seems like it not worth the money.  All that back and forth is unpaid labor! Also the cost of shipping materials and time spent going to and from the post office... Bleh!

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18 hours ago, Callie Beller Diesel said:

A non-refundable damn deposit! It’s a surprisingly effective screening technique. 

It's sooooo hard for me to talk about money, enforce these kinds of things, and put up boundaries. But eventually...and it takes a lot... if I'm pushed to far I suddenly have no tolerance. That's how I am feeling right now on a lot of fronts :) then I learn to stick up for myself :)

 

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