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Small bubbles in glazed bowls


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Hi all!

I'd love to get your thoughts on something!

I'm getting a lot of un poped bubbles in the glaze on the inside of my bowls. And on the outside, I'm not sure if it's pinholes or popped bubbles, but I'm getting quite a few of those as well.

I bisque fire to cone 04 and I glaze fire to cone 7 with the glaze rated for 1260C according to the store where I buy the powdered glaze to mix. I don't know if it's dirty clay and I should bisque higher or if it's over firing... according to the cones, I'm firing to the correct heat work.

I'm wondering two things. 1. Does anyone have advice on how I can prevent this from happening? Should I fire to 03 in the bisque? Fire maybe 5 C lower in the glaze firing? I currently have a 20 minute hold at the end of my firing. I was hoping this would make the bubbles burst and heal, but that doesn't seem to be the case... maybe it even made it worse? Not sure. 2. Does anyone have a recommendation for fixing such glaze defects after the fact so the piece isn't ruined? Simply adding more glaze and refiring doesn't make the bubbles go away. I tried like scrapping off the top of the bubbles with a broken piece of kiln furniture, rinsing the piece, and then adding a bit more glaze in those spots and that has worked a couple times. But I'd love to get your advice!

Here's another random question which maybe I should post under another topic, but while I have your attention :) When you're pricing commissions, do you take into account losses. Just as an example, maybe you tend to have problems with a glaze and know that 1 in 10 pieces won't meet your standard (in real life I'm having this problem on many more pieces). Or someone wants 10 plates but you feel like you should make 12 just in case... do you charge for 10 or for 12? Not sure if I am expressing my question well...

Thanks!

Caitlin

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Hi Caitlin!

I started out aiming for well heeled over cone six - where the seven cone shows a bit of movement - the red clay came out almost purple, and lots of bubbling. Now I aim for cone five, no hold at peak, but a long 100F less than peak hold, then controlled/slow cool to 1850F afore shutting off all heat. The bubbles/fizzing clears up very well.
I'm still bisque firing to cone 04, however, I'm holding at 1500F for a full hour, with ample oxygen/air flow (via powered kiln vent).

Also, one clear in particular seems to clear bubbles much better than the others I've tried, Wollastonite Clear (search "wollastonite clear" for pics, recipe, an' more!).

More on drop and hold: Drop-and-Soak Firing (digitalfire.com)

Commission, hrm, several folk recommend some $ up front, and clear agreements, good recommendations, both. As for how many to charge for, it takes x+n attempts to make x count, whether commission or not, eh? The n includes reclaim, dustbin, repurposed to planter, "second" shelf, and prime but doesn't match - all of which are on the maker, imo.
On t'other hand, if commission is for somewhat I/you/we don't make - not of the regular product line (or close to it) - then the requestor, they gonna have't' pay, PAY at at least some of the development, trial, proofing, testing, etc. COSTs. ...my opinion... 

Edited by Hulk
add Tony Hansen link
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@feistyfieryceramics  I didn't see what clay you were using.  I have always fired to 04 for bisque and 6 for glaze.  I recently tried a newer Laguna clay Speckled BMix.  I was shocked to see what looks ever so much like chicken pox or pimples allllllll over the bowls after glaze fire.  I used 2 different glazes that are bullet proof no matter what clay I put them on.  I called Laguna and they said that clay is definitely a cone 5 clay.  just a thought.

Roberta

20210527_135401_resized.jpg

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32 minutes ago, Roberta12 said:

@feistyfieryceramics  I didn't see what clay you were using.  I have always fired to 04 for bisque and 6 for glaze.  I recently tried a newer Laguna clay Speckled BMix.  I was shocked to see what looks ever so much like chicken pox or pimples allllllll over the bowls after glaze fire.  I used 2 different glazes that are bullet proof no matter what clay I put them on.  I called Laguna and they said that clay is definitely a cone 5 clay.  just a thought.

Roberta

20210527_135401_resized.jpg

Thanks Roberta. Unfortunately, the bubbles I am getting are just in the glaze and not in the clay. I double checked the sellers website and it says the max temp is 1280 C on the clay. So I think that isn't the issue, but thanks for responding!

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1 hour ago, Hulk said:

Hi Caitlin!

I started out aiming for well heeled over cone six - where the seven cone shows a bit of movement - the red clay came out almost purple, and lots of bubbling. Now I aim for cone five, no hold at peak, but a long 100F less than peak hold, then controlled/slow cool to 1850F afore shutting off all heat. The bubbles/fizzing clears up very well.
I'm still bisque firing to cone 04, however, I'm holding at 1500F for a full hour, with ample oxygen/air flow (via powered kiln vent).

Also, one clear in particular seems to clear bubbles much better than the others I've tried, Wollastonite Clear (search "wollastonite clear" for pics, recipe, an' more!).

More on drop and hold: Drop-and-Soak Firing (digitalfire.com)

Commission, hrm, several folk recommend some $ up front, and clear agreements, good recommendations, both. As for how many to charge for, it takes x+n attempts to make x count, whether commission or not, eh? The n includes reclaim, dustbin, repurposed to planter, "second" shelf, and prime but doesn't match - all of which are on the maker, imo.
On t'other hand, if commission is for somewhat I/you/we don't make - not of the regular product line (or close to it) - then the requestor, they gonna have't' pay, PAY at at least some of the development, trial, proofing, testing, etc. COSTs. ...my opinion... 

Thanks for the response. I have an old cromartie smartfire 3000 controller that didn't come with a manual. I only have the manual of a *similar* controller.  I unfortunately don't think I can program what you're describing...but I have heard rumors of a hidden button that one can use to link programs to allow you to make a more complex program than just two rates of rise, a hold, and a slow cool...maybe it is time to look for that button again. Ha!

So are you saying:

no hold at peak

Instead drop to 100 F below peak

Hold there?  How long should one hold there?

Then after that do a slow cool. How slowly?

Thanks for the advice about commissions too. I got a request for a commission for a 8-person salad bowl and a set of plates in a style related to some bowls I make (although not usually so big). They want the same glaze color and detail work as my bowls. For the plates they want to see a design before committing...so you actually also answered another question I had...how will I be compensated for that time I put into trying different designs.

It's all very interesting to think about. I have said to my husband, that a client shouldn't have to pay for my mistakes. But then again, I'm a human and not a machine. So some mistakes despite best effort to do a good job are unavoidable. And as my husband points out when he messes up at work and has to do things over again, he still get's paid for it. Ha! I never have anything crack or die in the kiln. But I like having extra just in case, so I guess if it is for my comfort, that is on me! I do have trouble getting plates off the wheel though, but I've ordered some batts. And I have this problem with the green glaze they want. And its problematic MOST of the time :( I better figure out this drop and hold things!

Thanks!

Caitlin

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Drop and hold might help - depends on what the problem(s) is/are, eh?

Yep, I'm holding at 1500F on the way up and down in my bisque fire, to burn out more stuff, and in the glaze fire, I'm turning to "low" when target temp is reached, then toggling the switches to hold for ...uhm, not remembering if it's half an hour or a full hour (will have to check my notes), then switches to low until temp falls to 1850F. yrmv - others drop more, perhaps 200F, and hold less. Mr. Hansen's article is worth reading, imo.

Your bubbles could be coming from the clay - glazes that clear the bubbles better won't show them as much. ...and your bubbles may be coming from the glaze (or both). Deduction can be a friend; firing schedules, clays, glazes.

Got pics?

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Argh. I wish I’d been able to divide the conversation before it got really going! 

The second question isn’t going to get as much response because it’s in the glaze section instead of the business section.  If you want, I can do some cut and paste, and set up that part of the conversation in a better spot.

As far as commission work goes, another thing to take into account is that while you are making a product, you’re also providing a service at this point. Not everyone has the skill to make pottery, so they’re asking you to use your skills for them, the same way they would for any number of other skilled professionals. A service provider does use a different pricing structure, although in our case, I’d suggest it be based on the retail value of the end product. No “bulk” discounts because there’s multiple pieces. Commissions aren’t bulk orders. I always make extra pieces or duplicates in the event something goes wrong. If the extras are successful and can be sold as part of my regular stock, I do that. I know of some other potters that do full dinnerware sets, but do so at a fixed rate. They make an extra couple of settings and include them in the order if they work out.

I also guide my customers firmly through what I am and am not willing or able to do. If I had a glaze that I didn’t have worked out 100%, I have learned not make that one available to the customer.  The reason being, if I’m going to promise specific pieces within a reasonable timeframe, I have to be able to make them confidently, and efficiently to be profitable. I don’t have time or space for problem child glazes in that equation. But if I have a very carefully evaluated situation where someone wanted something a lot, and they were a good customer who I’d worked with before and they were willing to pay with no complaints, I might make an exception. However I would make very sure that they knew there would be  no guarantees on delivery times to allow for things going wrong. I would only do this for someone I REALLY like, because I know there will be errors and waste. 

 

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12 hours ago, Pres said:

@feistyfieryceramics, why not aleve some of this guessing and post a picture of the glaze ware bowls that have the bubbles?

 

best,

Pres

'cause I had already put them back in the kiln :) without photographing them :) also my phone is bad at taking close ups. If this sencond firing after scraping off the tops of the bubbles  didn't rid of them, I'll try to take phtotos and then i will post them. Thanks!

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7 hours ago, Callie Beller Diesel said:

Argh. I wish I’d been able to divide the conversation before it got really going! 

The second question isn’t going to get as much response because it’s in the glaze section instead of the business section.  If you want, I can do some cut and paste, and set up that part of the conversation in a better spot.

As far as commission work goes, another thing to take into account is that while you are making a product, you’re also providing a service at this point. Not everyone has the skill to make pottery, so they’re asking you to use your skills for them, the same way they would for any number of other skilled professionals. A service provider does use a different pricing structure, although in our case, I’d suggest it be based on the retail value of the end product. No “bulk” discounts because there’s multiple pieces. Commissions aren’t bulk orders. I always make extra pieces or duplicates in the event something goes wrong. If the extras are successful and can be sold as part of my regular stock, I do that. I know of some other potters that do full dinnerware sets, but do so at a fixed rate. They make an extra couple of settings and include them in the order if they work out.

I also guide my customers firmly through what I am and am not willing or able to do. If I had a glaze that I didn’t have worked out 100%, I have learned not make that one available to the customer.  The reason being, if I’m going to promise specific pieces within a reasonable timeframe, I have to be able to make them confidently, and efficiently to be profitable. I don’t have time or space for problem child glazes in that equation. But if I have a very carefully evaluated situation where someone wanted something a lot, and they were a good customer who I’d worked with before and they were willing to pay with no complaints, I might make an exception. However I would make very sure that they knew there would be  no guarantees on delivery times to allow for things going wrong. I would only do this for someone I REALLY like, because I know there will be errors and waste. 

 

@Callie Beller DieselThanks Callie! I can put the commission question in another section myself... but maybe in a few days because I am kind of wiped out right now. I've been doing ceramics for 15 years but have only had my own studio for 6 months... and I have never really been interested in selling things, but a sweet older guy in the neighborhood of my studio insisted on buying some things as a gift and now the people he bought them for want to commission me, but I have no experience with that...and they are not very responsive. They loosely say what they want and then disappear and don't respond to emails...then when I follow up, they apologize for not responding, respond to 2-3 of my questions. And disappear again... I will learn a lot from experiences like this, I guess. Thank you for sharing your advice and your experience. I can learn a lot from that as well. And learning that one can say no and that somethings are not worth the time and stress is a super important lesson! Thanks again!

 

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9 hours ago, Mark C. said:

Need some photos 

In terms of commissions -the loss rate is always high with th an order-should you double the fee-well its up to the customer what is fair.

I gave up on special orders long ago myself.

Thanks! This is helpful! Even or maybe especially the part about maybe deciding not to do special orders :)

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special orders are always a problem.   whatever is in the client's mind does not translate to the potter.   

by the way, your location is not something to be afraid to mention,  the country is enough so someone does not feel foolish recommending an item that is not available where you live.

 

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10 hours ago, feistyfieryceramics said:

@Callie Beller DieselThanks Callie! I can put the commission question in another section myself... but maybe in a few days because I am kind of wiped out right now. I've been doing ceramics for 15 years but have only had my own studio for 6 months... and I have never really been interested in selling things, but a sweet older guy in the neighborhood of my studio insisted on buying some things as a gift and now the people he bought them for want to commission me, but I have no experience with that...and they are not very responsive. They loosely say what they want and then disappear and don't respond to emails...then when I follow up, they apologize for not responding, respond to 2-3 of my questions. And disappear again... I will learn a lot from experiences like this, I guess. Thank you for sharing your advice and your experience. I can learn a lot from that as well. And learning that one can say no and that somethings are not worth the time and stress is a super important lesson! Thanks again!

 

Run. Run like the wind from this order, non order.  imho

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If they’re being a nuisance either fire them as a client outright, or tell them if they want to go any further they need to make a design consultation appointment, at the end of which they will owe a deposit/consultation fee and work will begin. This will get rid of time wasters right quick! Anyone who is truly interested won’t balk, and will set up the appointment. This was the structure we used at a custom glasswork studio I used to work at. Just treat it as defining the services you’re providing, and politely inform them of your business model. 

Do not chase them if they’re not interested, that never ends well.

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

and I glaze fire to cone 7 with the glaze rated for 1260C

 

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

I currently have a 20 minute hold at the end of my firing. I was hoping this would make the bubbles burst and heal, but that doesn't seem to be the case... maybe it even made it worse?

The speed of the firing for the last 100C makes a difference in the final cone reached. If you are firing at 60C for the final hour 1260C is approx cone 9. If you are firing at 150C for the last 100C that is cone 7. Same temperature but big difference in cone reached. Now add on the 20 minute hold and you could very well be overfiring the glaze. Blisters are one of the trickiest things to sort out. If refiring makes the blisters worse then I'ld try a cooler firing. I'ld also strongly suggest that if you aren't already doing it to put some witness cones in your next firing.

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(and they are not very responsive. They loosely say what they want and then disappear and don't respond to emails...then when I follow up, they apologize for not responding, respond to 2-3 of my questions. And disappear again... I will learn a lot from experiences like this, I guess. Thank you for sharing your advice and your experience. I can learn a lot from that as well. And learning that one can say no and that somethings are not worth the time and stress is a super important lesson! Thanks again!)

 

This is all a bad sign for any business deal-I would just say no at this point

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On 6/22/2021 at 7:15 AM, Callie Beller Diesel said:

If they’re being a nuisance either fire them as a client outright, or tell them if they want to go any further they need to make a design consultation appointment, at the end of which they will owe a deposit/consultation fee and work will begin. This will get rid of time wasters right quick! Anyone who is truly interested won’t balk, and will set up the appointment. This was the structure we used at a custom glasswork studio I used to work at. Just treat it as defining the services you’re providing, and politely inform them of your business model. 

Do not chase them if they’re not interested, that never ends well.

@Callie Beller Diesel Thank you!

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On 6/22/2021 at 7:11 PM, Min said:

 

The speed of the firing for the last 100C makes a difference in the final cone reached. If you are firing at 60C for the final hour 1260C is approx cone 9. If you are firing at 150C for the last 100C that is cone 7. Same temperature but big difference in cone reached. Now add on the 20 minute hold and you could very well be overfiring the glaze. Blisters are one of the trickiest things to sort out. If refiring makes the blisters worse then I'ld try a cooler firing. I'ld also strongly suggest that if you aren't already doing it to put some witness cones in your next firing.

Hi all! I have some photos now and a bit more info from trial and error and some hypotheses I'd love to get all your thoughts on .

I fire with cones about every 4 firings to make sure my program is still on track, so although my termocouple doesn't read correctly, I know that I am firing to 04 for bisque and 7 for glaze.

With my medium sized bowls (20 cm x 8 cm), I often have 2-10 small bubbles in the top/inside surface and a couple what I think are pinholes on the underside. My green colored glaze is the most problematic. The pieces I describe below were all in that glaze.

I thought maybe I was over firing, so I fired this time to cone 6 (I uses  cones to confirm. Also the middle shelf is always a bit hotter, and the bottom a bit cooler). My big bowl (32 cm x 11 cm after glaze firing) was fired on the top shelf  and it is by far the worst I've ever seen in terms of bubbles! And this time it looked like mostly popped rather than intact bubbles. The small bowl and the plate had no bubbles on the upper surface, but the bottom of the plate has pin holes I think.
 
So I guess lowering the temperature didn’t help?
 
I wonder to myself if the pieces on the middle shelf weren’t as problematic as the big bowl because the middle shelf would have been a bit hotter than the top shelf?
 
Or could it be because bowl and plate were thin? Could they have been heated more thoroughly in the bisque so that organic material would have been better able to burn out?
 
Or did the big bowl really not get hot enough in the glaze firing because I lowered the temperature AND because it’s thicker?
 
I use a white-light colored stoneware. But I wonder, could my big bowl clay be “dirty” because it is recycled and maybe it h a lot of organic matter in it from that? The recycling slop is quite black when I dig it our of its smelly depths. And I tend to prefer working with recycled clay for medium to large pieces because I like my clay a bit firmer than it tends to be straight out of the bag. So another difference besides location in the kiln and thickness could that I may have used fresh-out-of-the-bag-clay for the plate and small bowl vs recycled clay for the big bowl.
 
 
What I did to successfully “repair” the glaze on the last set of medium size bowls that had some bubbles was to rub/grin the tops off the bubbles with a piece of broken kiln furniture and then get some fresh glaze in the holes. That seems to work really well for the bubbles on the inside of bowls, but I’m not sure what to do about the “pin holes” which tend to be on the underside.
 
Unfortunately, I have to get this big bowl right for a client. I made two more today. I’d love to know how to improve the situation before I put the time and electricity into firing and finishing them.
 
Thank you so much for your time!
Caitlin

Due to files size limits, I think I have to make multiple posts to get all the photos in.

 

114853551_bigbadbowl.thumb.jpg.07c42b604e82682f483a1be125cc864e.jpg

 

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5 hours ago, feistyfieryceramics said:

What I did to successfully “repair” the glaze on the last set of medium size bowls that had some bubbles was to rub/grin the tops off the bubbles with a piece of broken kiln furniture and then get some fresh glaze in the holes. That seems to work really well for the bubbles on the inside of bowls,

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.

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