Terrible pinhole problems in oribe glaze

[thiamant]

I tried this glaze on test tiles before without much problems. When applied to a bigger piece (same body, same glaze) a lot of pinholes show up.... This is an oribe glaze with black copper oxide, I was warned that it had a tendency to produce pinholes. But this is a bit crazy isnt it?

Glaze recipe:

https://glazy.org/recipes/133488

 

 

Same glaze applied on top of a white glaze, this time no pinholes:

[Hulk]

Hi again Thiamant,

Your work area (background), so neat and clean!

The defects - looks more like craters than pinholes; do the openings go all the way to bare clay?

My guess would be that the defects are related to the clay, firing, and how well the glazes heal over:

  clay - big craters, bare clay at bottom may indicate that the clay was gassing (expelling gasses); same batch/bag of clay may matter here, and thorough bisque firing

  firing - a bit hotter, and/or more time at peak may generate more gassing - a bit lower peak might help; a drop and soak might also help - I drop 100F from peak and hold for half hour

  glaze - the white glaze may stay melted longer, flowing back together after the clay stops fizzing

One more idea - is the problem piece thicker than the test tiles and the tumbler?

I'm curious to see what others may offer. Please do post back updates on your findings!

[oldlady]

thiamant,   since you have that pot available, you might want to test the glaze for leaching.   i do not know what recipe was used to get that green but i used to use a very widely available recipe called Oribe Green.  when i tested it by putting part of my test in vinegar overnight, it changed colors.  the test was a flat disc and i put it into a plastic bag with half of the disc in the vinegar and the top half was not covered with the vinegar.   the test showed that the glaze leached chemicals and was not good for food use.  a dark sandy residue was in the bottom of the bag.  i stopped using it because we never know what kind of food might get put on our plates.  i know your vase will not be used that way but it will not hurt to test your glaze.

[Callie Beller Diesel]

All of the cone 10 oribe glazes I’ve ever worked with were very fluid, and it seems like this example is no exception. In addition to not having much alumina in this recipe, both iron and copper will act as additional fluxes, although most glaze software doesn’t incorporate that into their calculations. Your glaze is, like many oribe glazes, probably over fluxed, so it’s blistering because it’s too hot.

I notice that the white glaze that you’ve layered the oribe with is a matte of some sort. I’d say the oribe glaze is borrowing enough silica and alumina from the glaze underneath to balance itself out a bit, and be less of a problem child.

I have to second Oldlady’s opinion about not using this one for food vessels. Barium carbonate in that quantity, insufficient alumina and copper in that saturated level will often cause glazes to be soft.  I only mention it because it looks like that cylindrical piece is of a size to be used as a beer cup.

[thiamant]

First of all thank you for your support and help!! 

I think the openings go all the way into the clay, maybe you can check the picture below. Probably it's overfired, I fire it slow up to 1260ºC with a 30 minutes soak at the end.

200        100 º/h
1.050        142 º/h
1.175        100 º/h
1.264        60 º/h
1.264    000:30 soak   
 

I'm suspecting the body might be also responsible, since I just noticed a small number of pinholes in other glazes I tried, like the temmoku showed below and also the white. This clay body has 40% very fine grog.  Maybe that contributes too. What should I try first? Changing clay body ? adding silica/alumina to the glaze? how much would you add?

By the way, I'm not using any of the oribe pieces for functional ware, I'm aware of the toxicity problems of barium carbonate and copper oxide.

[thiamant]

1 hour ago, Callie Beller Diesel said:

 

I notice that the white glaze that you’ve layered the oribe with is a matte of some sort. I’d say the oribe glaze is borrowing enough silica and alumina from the glaze underneath to balance itself out a bit, and be less of a problem child.

 

Yeah, a very nice semi matte, very simple 50 soda feldspar, 30 kaolin, 20 dolomite

[liambesaw]

Lots of gassy ingredients in the recipe too.  Calcium carbonate, barium carbonate, bone ash, all have high loss on ignition and are sources for bubbles.

[thiamant]

1 hour ago, liambesaw said:

Lots of gassy ingredients in the recipe too.  Calcium carbonate, barium carbonate, bone ash, all have high loss on ignition and are sources for bubbles.

To be fair those are fairly common materials used in glazes, even as a group.

[Callie Beller Diesel]

Off-gassing materials is less of a problem at cone ten than it is at cone 6. It was one of the things I really had to adjust to when I switched from firing high temp to mid range. Because cone 9-10 firings are usually hotter and longer, the carbonates and other materials have longer to leave the proverbial building. It’s more forgiving that way. 

I think you have 3 things going on here. The grog is probably contributing to the problem, which is why you have some tiny but much less significant pockmarks in the tenmoku. I’d have to see the recipe to confirm. 
 

I suspect your matte glaze is a cone ten glaze, the oribe is a cone 8, which is common for the type, and you’re firing to cone 9. The matte glaze looks a little underdone by itself, the oribe is overdone, and together they work it out amongst themselves by trading materials. 
 

Also, I have a nice oribe glaze recipe that doesn’t have the barium if you’d like it. 

[liambesaw]

48 minutes ago, thiamant said:

To be fair those are fairly common materials used in glazes, even as a group.

Indeed, but not at those levels.

[thiamant]

34 minutes ago, Callie Beller Diesel said:

Off-gassing materials is less of a problem at cone ten than it is at cone 6. It was one of the things I really had to adjust to when I switched from firing high temp to mid range. Because cone 9-10 firings are usually hotter and longer, the carbonates and other materials have longer to leave the proverbial building. It’s more forgiving that way. 

I think you have 3 things going on here. The grog is probably contributing to the problem, which is why you have some tiny but much less significant pockmarks in the tenmoku. I’d have to see the recipe to confirm. 
 

I suspect your matte glaze is a cone ten glaze, the oribe is a cone 8, which is common for the type, and you’re firing to cone 9. The matte glaze looks a little underdone by itself, the oribe is overdone, and together they

Also, I have a nice oribe glaze recipe that doesn’t have the barium if you’d like it. 

The matte glaze is looking great on other bodies. Like the one on the cylinder. But yeah it looks like overfiring might be the problem for the oribe.

Sure please share I will test it when I have time! I wanted to make oribe teapots (at least on the outside) so having no barium might be good idea. I will also  test my oribe on a different clay body with much less grog, and see what happens. 

[thiamant]

5 minutes ago, liambesaw said:

Indeed, but not at those levels.

Tbh I dont even know why there is so much barium in this glaze.

By the way, the temmoku is Leach 4321 with 10% RIO.

Such a shame, it looked so good on this test tile.

 

[liambesaw]

At cone 10 reduction barium is a very good glassy flux

[Callie Beller Diesel]

Carolina Oribe

29 Custer (potassium feldspar)

24 silica

21 whiting

12 EPK (China clay)

7 talc

1 bone ash

5 copper carb. 

 

I've mostly used it in reduction. It does get some nice crystals, and can shift towards the blue end of the spectrum where especially thick. I think it stays more green in oxidation. 
 

Leach 4321 was one of my go-to’s, but as a celadon, not a tenmoku. It never gave me any grief. Yeah, test your other clay body and see if that affects things. 

[neilestrick]

It definitely looks over-fluxed to me. I'd try adding equal parts kaolin and silica in 3% each increments. At some point it's going to affect the color and look of the glaze. You may or may not get it to be stable before that happens, but it's worth testing. 

There are a lot of Oribe glazes out there that don't have barium, and are able to hold their copper pretty well. Personally, I'd ditch this recipe and find a better one.

[Bill Kielb]

17 hours ago, thiamant said:

Same glaze applied on top of a white glaze, this time no pinholes:

 

It is interesting if you look at that recipe on Glazy you find the owner says it’s a new glaze and he is currently testing. If you look at the Stull chart it appears in an area within Stull that is typically not predictable and basically not good as a stabile glaze. Regionally  most glazes in that area are intended for a lower cone or if fired higher intended to run over another glaze for decoration or perhaps crystalline,

So it has very little silica and alumina and seems to fire in an area we are accustomed  to lowfire and earthenware firing temperatures or ........ a glaze that is guaranteed to run at cone 10 so just apply it to rims over existing glazes and let it go..

I take the author for his word and expect he will continue testing and post pictures when he is done. For now I would expect this glaze to run. So for cone 10 use maybe let it run over existing glazes for affect.

Another interesting observation in your firing schedule seems to be fire to cone 9 with a thirty minute hołd at the top. Is your intention to drive this to cone 10?

 

[thiamant]

Actually I am the one who posted this. A friend gave me the recipe and I uploaded it to check stull chart etc. This is supposed to be a 1260C glaze.  

[Bill Kielb]

3 minutes ago, thiamant said:

This is supposed to be a 1260C glaze.  

What makes it a 1260 glaze? Si:al. Very low for high fire stabile glaze.

[thiamant]

13 hours ago, Bill Kielb said:

What makes it a 1260 glaze? Si:al. Very low for high fire stabile glaze.

I think this is a feature of oribe glazes. 

 

[Bill Kielb]

2 hours ago, thiamant said:

think this is a feature of oribe glazes. This is from John Britt's high fire glazes book:

Yeah, have the book somewhere here, and have actually met John and had interesting conversations with him, nice guy.   I would not expect the firing range of this glaze to be cone ten and durable nor it be a trouble free composition from its chemistry and placement in Stull as well as comparing it with other similar glaze formulas or even limits. 
 

To be fair It does look like his focus here is color though not necessarily durability, stability, ease of use, melting range.  Having said all that, the next step would be to test for which you have begun and likely are concluding that this glaze needs research to fire in this range or some range effectively. Eventually once  that is figured out then testing durability of the successful formulations would likely be your next thing I guess. So you are on the testing pathway.

Still curious why a thirty minute top temperature soak was added to your firing schedule though.

[Callie Beller Diesel]

@Bill Kielb Oribe glazes are a Japanese style of glazes and work that have a long and interesting history dating from the 16th century. There are still potters making Oribe wares today in Japan, and it’s part of a wider aesthetic there. When the Leach/Hamada influence hit the western world, the glazes were brought over and incorporated into a lot of college lexicons, often without a lot of context. (Helloooo colonial attitudes!) Lots of westerners looked at the runny green glaze that pools blue, and said some variation of “oooh! Pretty!” And proceeded to use them, or to reformulate with more local materials, or simply tried to recreate the effects to use in their own work. The main characteristics that people seem to hold to is that the glaze is a high temperature one, a copper saturate, and is very fluid/low in alumina. Crazing isn’t considered a deal breaker with them either. No, they don’t hold up to Stull chart durability standards, and many of them are easily altered with an acid test. That doesn’t mean that they’re not lovely, or that people aren’t inclined to use them in an artistic practice. I personally wouldn’t use them as a liner glaze, but they do have places in decorative areas.

[Bill Kielb]

4 minutes ago, Callie Beller Diesel said:

I personally wouldn’t use them as a liner glaze, but they do have places in decorative areas.

Absolutely agree. Many folks I know use them for their decorative runny nature  over other glazes. They get very good at knowing just how far a rim dip will travel over some of their goto glazes. Pretty impressive actually and often beautifully decorated work. Occasionally find them grinding the bottom of a pot and muttering under their breath though.

[thiamant]

10 hours ago, Bill Kielb said:

Still curious why a thirty minute top temperature soak was added to your firing schedule though.

A couple of reasons. It helps me ensure that the top temperature reaches all the pieces in the kiln. I get 0.5 cone almost cone 10 without having to push to the 1280C range. And also I heard it helps healing pinholes. 

[liambesaw]

7 minutes ago, thiamant said:

A couple of reasons. It helps me ensure that the top temperature reaches all the pieces in the kiln. I get 0.5 cone almost cone 10 without having to push to the 1280C range. And also I heard it helps healing pinholes. 

Drop and hold helps with pinholes better than a top soak.  Don't ask me why, I'm unsure. Maybe some carbonate or sulfate in the clay stop dissociating when the temperature drops 100⁰f, or maybe it's just magic, but it works much better in my experience with dirty clays.

[Bill Kielb]

24 minutes ago, thiamant said:

A couple of reasons. It helps me ensure that the top temperature reaches all the pieces in the kiln. I get 0.5 cone almost cone 10 without having to push to the 1280C range. And also I heard it helps healing pinholes. 

There are times when it actually makes the pinhole problem worse. A bit counterintuitive I know but definitely worth googling digital fire for a good read.

As far as the heatwork issue, definitely holds add heatwork and moves your firing upward. As far as same top temp everywhere, sort of ignores the value of heatwork really as pieces that see the radiation get more heatwork. I am not convinced holding at the top temperature for evening things out is better than a slow final rate really.  Just something to think about.