Quick cool glazes

[Mudfish]

Any suggestions on a cone 6-8 glaze that can tolerate a fast cool? I seem to never cool my kiln slowly enough. Thanks

[Bill Kielb]

21 minutes ago, Mudfish said:

Any suggestions on a cone 6-8 glaze that can tolerate a fast cool? I seem to never cool my kiln slowly enough. Thanks

Not sure I understand, are you seeking a matte finish and cannot get results? If yes mix up a true matte, doesn’t depend on slow cooling.

[Mudfish]

Yes I love matte glazes. Currently I've been using a glaze mix...well lets call it Mystery White" its a combination of a few different matte whites...don't ask for an explanation, lol. I have a lot of it and I hate to waste it, but I'm getting these tiny broken blisters with every firing. Im assuming its because I'm not cooling slowly enough. 

[Callie Beller Diesel]

That can get really complicated to try and troubleshoot. Pinholes can have a LOT of causes. Matte glazes can result from a few different mechanisms that involve melt and/or refractory materials. Some of these things may or may not be overlapping to cause your problems. Without knowing the composition of your glaze, we’re going to be guessing a bunch at what’s going on. In a universe of infinite possibilities, it’s possible to figure this out. But it will likely take a lot of testing on your part. A lot of ceramic people do love a good project, so if this is something that gets you excited, we can help. It will most definitely be easier to start from scratch, and find a glaze that suits your clay and firing cycle though.

So. How much time do you want to spend trying to rescue a mystery glaze, and what clay are you using, and what firing cycle? That last one will be needed in either event.

 

 

[Mudfish]

I have a question on Copper Salt / Yellow Salt glaze formulas on Glazy - Here is the formula for Copper Salt 

Amount
Neph Sye A270	71.5
Dolomite	23.5
Kentucky OM #4 Ball Clay	5
Total base recipe	100
Zircopax	16
Bentonite	2
Copper Carbonate	1
Total	123

Here is the formula for Britt's Salt Glaze 
Amount

Nepheline Syenite

71.6

Dolomite

23.6

Ball Clay

4.8Total base recipe100

 Zircopax

17.9

 Bentonite

4

 Red Iron Oxide

1.1Total123     Both formulas are almost identical. On some of the descriptions/photos is describes this salt glaze as glossy, on the Copper Salt, it is matte. Also, on another post on Glazy for this same glaze , the photo shows it as a matte with iron speckles on iron rich stoneware, and matte also on some porcelain mugs. So, is salt glaze of this composition matte or glossy? 

 

 

[Bill Kielb]

30 minutes ago, Mudfish said:

So, is salt glaze of this composition matte or glossy? 

Fired to the proper cone and by composition we would expect it to be matte because the SI:Al  ratio is 5 or less. (UMF and extended UMF) When the fired result differs from the compositional result we look for reasons why. Knowing the expected texture of a glaze is often super helpful and often reveals a glaze is underfired for instance and not fully melted in the case of a glossy glaze that mysteriously fires matte.

[Mudfish]

Ok thanks Bill. I thought it would be matte also. I will make up a batch and give it a test in my kiln. I did pitch ALL the pin-holey mystery glaze I had.  

[Min]

On 3/26/2021 at 7:27 AM, Mudfish said:

Any suggestions on a cone 6-8 glaze...

Yellow Salt and Copper Salt recipes you posted are cone 10 glazes. I haven't fired them to cone 8 but I would suspect they will be immature and not properly melted. They will also be more matte when underfired versus fired to maturity.

[Mudfish]

You are right. I thought maybe I could add 3% or so of a frit. Maybe that would bring it down to cone 6-8 level. 

[Min]

You could do some tests with that glaze by adding a boron frit but why not just use a cone 6 glaze to start with?

Are you looking for a cone 6-8 matte glaze for functional work that doesn't cutlery mark or stain or is this for non-functional work? Also, I'm wondering if  you are using a wide firing range claybody since you are firing cone 6-8 or a cone 6 body?

[Mudfish]

Yes. A 6-8 good functional matte. I use a stoneware claybody that is mostly goldart with some hawthorne, ball clay and neph sy

[Mudfish]

My kiln fires sometimes one cone difference from top to bottom so this is why I just want to play it safe and use a wide firing range glaze, preferrably

[Callie Beller Diesel]

A quick google using terms “yellow salt glazy” finds this recipe listed for both John Britt and Ayumi Horie. Both state they’re cone ten glazes. I have come across references for it being used at cone six, but not with success.

 From personal experience: yellow salt at cone 10 has a pleasant, soft sheen and a lot of subtle, visual depth. It gets glossier if it’s hit in an atmospheric kiln with extra sodium. However, the glaze is soft, and not a good candidate for liners or other working parts of functional work. With this amount of sodium, it crazes. It’s not durable over time.  If it’s underfired at cone 6, none of these problems will be improved.

 

[Magnolia Mud Research]

I would take my standard clear glossy glaze recipe, add some Zircopax for whiteness, use 2%, 4%, 8%, 16%, 24% Zircopax as a first test set to bracket the amount needed; then think about tweaking within a bracket.  if not enough matteness,  maybe add some more clay or alumina hydrate with a similar approach;  
you already know how your clear glossy glaze performs on your ware, in your kiln, fired your way; this means you have a big head start over any recipe that you have not used. 

LT 

[Mudfish]

Thank you, M. M Research.... I like your idea, my issue is I really do not have a clear that works. I've always used matte even when I was firing  with electric. I did this suggestion of yours with Hal's Pale Apple...  I chose Pale Apple because of its wide firing range.  I added 4% u-pax. I like the color and I can tell if I add a bit more u- pax it will matte it up a little more...its just that my (converted) kiln cools off so quick and I havent mastered the slow cool and targeting the temps to do holds...so pale apple crackles if it is cooled off too quick. Honestly, I would just like to nix the tedious manual slow cool process, or at least use a glaze that is not so sensitive. Pale Apple is a high feldspar...so there ya go. I did find a matte base Cooper formula on the Sankey glaze data site. It is in the cone 5-8 range. Im going to test that. If anyone has another glaze suggestion that would be great. Thanks :) 

[Bill Kielb]

11 minutes ago, Mudfish said:

Im going to test that. If anyone has another glaze suggestion that would be great. Thanks

Here is one to test (as always no guarantees). If you want it less matte, just add more silica till it’s the sheen you like. It will go all the way to gloss.

 

 

[Min]

I think we need to back it up a little bit here and isolate the individual components of your glaze testing and firing and get those sorted out one by one. Please correct me if I'm wrong but my take on your situation is this:

- you are firing reduction and after reaching your firing cone you are shutting down the kiln

- your kiln is cooling quickly, don't think we know how quickly or what type of kiln it is. Soft or hard brick? Size of kiln? 

- you have a 2 cone difference between top and bottom or middle

- cone 6 clay?

- how are you stacking?

- you will be making functional ware with durable glazes

- you don't have a glaze that fits your clay without crazing, gloss or matte or in-between. 

- we don't know the recipe for Pale Apple or for the Cooper recipe (from Sankey) but the Pale Apple crazed. (should't be dependant on a slow cool not to craze)

[Mudfish]

31 minutes ago, Bill Kielb said:

Here is one to test (as always no guarantees). If you want it less matte, just add more silica till it’s the sheen you like. It will go all the way to gloss.

 

 

Thanks Bill

I will try this out also

[Mudfish]

21 hours ago, Min said:

I think we need to back it up a little bit here and isolate the individual components of your glaze testing and firing and get those sorted out one by one. Please correct me if I'm wrong but my take on your situation is this:

- you are firing reduction and after reaching your firing cone you are shutting down the kiln

- your kiln is cooling quickly, don't think we know how quickly or what type of kiln it is. Soft or hard brick? Size of kiln? 

- you have a 2 cone difference between top and bottom or middle

- cone 6 clay?

- how are you stacking?

- you will be making functional ware with durable glazes

- you don't have a glaze that fits your clay without crazing, gloss or matte or in-between. 

- we don't know the recipe for Pale Apple or for the Cooper recipe (from Sankey) but the Pale Apple crazed. (should't be dependant on a slow cool not to craze)

Well Min, you make my issues sound as much fun as they truly are! So, here is more info on my process:

- I do not shut down my kiln after a cone 6-7 reduction fire. I wish I could.., but I know it would cool WAAAY too fast.

- yes, my kiln cools quickly. The first time I fired it I did just close the damper, off with the burners...and within less than 4 hours it was about 300*F . Thats quick!

- I do have a difference between top and middle. I am getting better at firing to an even temp, lately. I just had to learn the ropes with it. For now, I just want to be safe and use glazes that have a wide firing range.

- cone 6 clay. I mix my own. Its mostly Goldart 65 parts, 20 parts hawthorne, 5 parts neph sy, 5 om4,  5 parts redart. 

- I stagger the shelves when I stack. first shelf sits about 5 inches from the floor

- I make mostly functional ware, some thrown and attached sculptural forms that are based on functional ware, but mostly I make functional ware

- yes, durable glazes

- not much luck with glazes. I think mostly because I've been wasting my time trying to salvage some foo-boo glaze I had. I'm done with that and in search of a reliable base glaze

- Hal's Pale Apple formula :

 

Forshammar Feldspar	40
Cornwall Stone	20
Kaolin	20
Whiting	20
Zinc Oxide	7
Total base recipe	107
Rutile	6
Yellow Ochre

 

...And I was shocked at the actual results I got from Hal's Pale Apple. From the pic, it looks matte. Its not. Not in my kiln. It looked more like a celadon, with crackles everywhere. So I fired it again, with a slow cool, and the crackles were gone. I was so worried about the crackle business, that I did a very slow cool. All I'm saying is, after a ten hour fire, doing another 4 or five hour slow cool is a lot of time. If I have to operate this kiln this way, ok, but I would like to not have to worry so much about the slow cool process. I would like to use a base glaze that is not so prone to crackling, and has some wiggle room with the maturing cone. and matte. 

Maybe I'm asking too much, Idk. Yikes.

Thank you for your attention, Min. I do appreciate the suggestions and your knowledge. I'm new at this. I have been using the touch and go kiln types for years, but I have always loved reduction. 

[neilestrick]

@Mudfish How is your kiln constructed? Is it an electric conversion, soft brick, fiber...? How big is it?

I think the first thing to figure out is evening out the temperature. You're not going to get consistent results from your clay or your glazes if you've got a cone difference. Especially when dealing with matte glazes, one cone can have a big effect on melt and durability.

Definitely don't waste your time on old glazes that don't work. Runs lots of test, and don't assume that because a glaze works for someone else that it will work the same for you. Different clay bodies, firing schedules, raw materials, etc will all affect how a glaze behaves. I don't think I've ever used a 'tried and true' glaze without tweaking it. But you should be able to find one that's close to what you need and then just tweak it for melt or fit.

[Mudfish]

its an electric conversion 27"x28".  I sealed up some places where there were some brick damage, so I think this will help me in evening out the top & bottom temps. 

Thanks, Neil

[Callie Beller Diesel]

I went through this thread and carefully re-read things that got mentioned more in passing that I think are key to understanding your problems. 

-You mention that your kiln is a conversion, and that you’re firing with gas. I assume this to mean you’ve changed an electric kiln to a gas.

-You mention that your firing cycle going up is 10 hours, and that a natural cooling cycle is only 4 hours. (!!!)

-There’s more than a cone difference between top and bottom shelf.

-The pale apple glaze recipe has a lot of zinc, which shouldn’t need a slow cool to be at least somewhat matte in that quantity.

-The only time re-firing glazes fixes crazed ware in the way you describe with the pale apple glaze is if the glaze wasn’t fully formed in the first place.

-You’re placing your first shelf 5” off the bottom of the kiln, and I assume the space underneath is your firebox.

Typically electric kilns that get converted into gas are in the 7-10 cu foot capacity range. If you’ve got a large amount of void space, there’s going to be less thermal mass to hold in heat to cool off the load at what I would consider a reasonable rate. A kiln should take the same amount of time to cool as it does to heat, without any  additional down firing. That’s true in both electric and gas kilns that are properly constructed. 

I don’t think you have a recipe problem. I think you have an equipment problem.

[Mudfish]

Thank you, Callie

I thought zinc was a flux in glazes, I actually omitted it, because I thought it would make it glossy. I'm going to maybe make a small batch and re-test it

thanks so much

 

 

[Callie Beller Diesel]

Zinc is a weird one. Yes, it’s a flux, but it also stays active over a relatively wide temperature range, which allows more working time for a glaze to form crystals that are one of the mechanisms that create matte glazes.

My point is that your kiln isn’t allowing enough heat work to happen on the cooling side of the cycle, where much of the reactions and phase changes occur. It sounds like its under-insulated and too difficult to control to get the types of glazes you want. Chemistry isn’t going to fix that. You need to sort your kiln out before we can fine tune any matte glazes.

[neilestrick]

1 hour ago, Mudfish said:

its an electric conversion 27"x28".  I sealed up some places where there were some brick damage, so I think this will help me in evening out the top & bottom temps. 

Thanks, Neil

How is set up? Is it an updraft or downdraft? What size shelves are you using? Where does the burner come in- floor or wall? THIS conversion system was worked well for several forum members. The main problem people have with conversions is still loading them like an electric kiln. At the very least, you have to use smaller shelves so the thing can breathe. Doing a downdraft makes them work the best.

I'm surprised your kiln is cooling that quickly. Yesterday I fired my electric kiln of that size empty to cone 6 to calibrate my thermocouples, and it took a good 12 hours to get down to 400F. Make sure your flue opening is sealed tight at the end of the firing to keep air from flowing through. If you can seal the burner port(s) do that as well.