Celadon flaking pre-firing

[Transfunctional]

Howdy y'all, I was wondering if you could help me with this issue I have been finding with Celadon glazes, it seems that with the 2-3 celadon glazes 

the dried coating of glaze like to flake off on its own or is just exceptionally fragile before its fired, the slightest touch of the rim can encourage it to come off during the loading process

I've attempted including macaloid or epsom salts to discourage hardpanning and encourage a bit more shrinkage as it seems the glaze coat doesnt shrink as much as the bisqueware would like it to perhaps?

I would at this point try to thin the recipe out and attempt doing multiple thin coats? but I've been encouraged/read that celadons need a rather thick glaze thickness to work properly

Is this an issue that would be solved by once firing with classic celadons? As I understand the origins of celadon glazes hail eras where bisquing was a bit less common

What're yer thoughts n' suggestions?

 

the recipe i'm using below:

custer feldspar : 66

Silica : 14.3

Whiting : 14.3

Soda Ash : 6.8

RIO : 0.25

+Macaloid : 1

[Min]

 Are you dead set on not having any clay in it? If so I would get some Magma (available at Brackers). It will both suspend the glaze plus make it more durable in the raw state. It does take longer for the glaze to dry when using it though. Is crazing an issue?

[Callie Beller Diesel]

I second the notion that the lack of clay is going to affect your application, plus how durable the dried glaze is on the pot. It looks like an odd recipe to me. If you’re married to this recipe, we can help you tailor it, or I’ve got a few old ones in my books from college if you’d like to substitute. Or Glazy is always a great resource for new stuff, and it has the benefits of pictures that my glaze book doesn’t have.

Traditional cone 10 celadons do look a lot better with a thick application. The ones I used personally were always dipped on bisque, and all contained clay. Those ones did benefit from the Epsom salts, so the drying was slowed, and application marks could smooth out. The ones I’ve used were not given to much movement in the kiln, so every drip showed. They were pretty user friendly to load though.

 If you’re talking about once firing traditional celadons that were formulated somewhere in ancient China/Japan/Korea, many kiln sites did single fire to save labour and fuel. But the recipes you’d find in North America for the last 50+ years reflect local practices and materials, and aren’t the same. 

 If you do want to try once firing though, maybe @oldlady  can give you better tips on that. She’s our local once fire person. 

 

[Transfunctional]

I actually found this recipe on glazy which is allegedly a modification of the Ice Trap celadon from John Britt's high fire glaze. I've had some good results from it in the past, very pale matte blues with nice carbon trapping.

It has always crazed in my experience- yea, the drips always show pretty clearly, the glaze applied to bisque drys slowly

speaking to the addition of Magma, isn't magma just a thixotropic additive like bentonite/veegum/macaloid and wouldn't the macaloid provide/aid the flocculation / suspension of the glaze I would want?

I'd be curious to see some recipes you've got with better application properties or if you've suggestion for additions/alterations that might help with this hellish application 

[Min]

5 hours ago, Transfunctional said:

speaking to the addition of Magma, isn't magma just a thixotropic additive like bentonite/veegum/macaloid and wouldn't the macaloid provide/aid the flocculation / suspension of the glaze I would want?

Unlike some of the other flocculants Magma will work in glazes having zero clay. It also toughens up the raw glaze coating on the pots so you don't get the fragility you mentioned and doesn't cause the glaze to "sheet" like CMC can.

[Callie Beller Diesel]

Okay. I can’t show you a sample of this glaze at the moment because the jug that I used it as a liner on is full of iced tea, lol! But it is softly matte, and does have a little carbon trapping around the rim where soda hit it. It crazed on my clay body at the time, but that may not indicate anything for how it will behave with your materials. I got this recipe from a handout in college, from Sam Kwan when he did a workshop with us.

There ARE some slight issues chemically with this recipe, but it’s a starting point, and it is fixable. As written, it’s got a flux ratio of 0.19:0.81, which isn’t ideal for durability. The silica: alumina is 9.81, so that part’s okay. My pitcher seems to be holding up, but it doesn’t get heavy use. 

Sam Kwan’s celadon (cone 10 R)

34 potash feldspar 

27 wollastonite

21 silica

15 grolleg

3 talc

add 1% turquoise stain

At the time, Sam acknowledged that the community at large considered using stain as a colourant to be “cheating” and that he really didn’t care. It got him the colour he wanted, even on stoneware. Because of the use of stain, it’s much less material sensitive than reduction celadons that use iron.

IF you go decide to alter or fix this recipe, or if you are still looking for a more “traditional” celadon that uses iron in some form as a colourant, there’s a few things to keep in mind.

Generally speaking, high fire celadons will drift more towards the blue end of the spectrum if they’re used on porcelain, and they’ll drift more towards the green end if you’re putting them on stoneware, or if you use kaolins and feldspars that have iron or titanium trace. Hence the use of grolleg, instead of the more typical EPK. When this recipe was given to me 20 years ago, the general assumption was that grolleg was “cleaner” than EPK, although we didn’t have easy access to comparative materials analyses at the time. The original recipe called for G200 feldspar which isn’t available now, but Mahavir can be substituted, and would be a better choice than Custer.

Because talc supplies have become an issue lately and new sources have more iron and titanium, I put the recipe into glazy to see what simply removing it did. The flux ratio improves a hair to 0.21:0.79. The silica:alumina ratio lowers, but only slightly and it’s still in an acceptable range and easily adjusted.  The talc may have been in the original recipe because at the time it was a common antidote to crazing. There’s other ways to do that though.