Terrible pinhole problems in oribe glaze

[thiamant]

Ok, can you guys help me adjusting the firing schedule to incorporate this drop and soak idea? Should I reduce the speed in the last segment?

[Bill Kielb]

1 hour ago, thiamant said:

Ok, can you guys help me adjusting the firing schedule to incorporate this drop and soak idea? Should I reduce the speed in the last segment?

60c per hour is generally a good speed from the middle column of the Orton cone chart.  The rule right on the chart is the last segment at 60c per hour in about the last 100c of the firing. So cone 9 for you is 1260 minus 100c means the last segment starts at 1160c and fires at 60c per hour to 1260c. This should get your cone 9 cone to bend fairly close to the predicted. From there you added a 30 minute hold to get your heatwork close to cone 10 I believe,  and a drop and hold to try would be drop 100c and hold at 1160c for 20-30 minutes.

The concept is the fired surface tension of a particular glaze is too high at peak temperature for the glaze to heal so dropping some amount and holding or soaking gets the glaze to a point that it still flows but now heals as the surface tension reduces. Finding the best drop and best hold time takes some experimentation for a particular glaze.

Some folks just use it for most of their glazes to avoid issues with a particular glaze. I think @Hulk detailed his earlier in this thread and digital fire has a generic one or two. Folks usually develop what works best for them, their glaze, and their firing temperature by trial, improvement and more trial,  so a standard one likely does not exist.

Intuitively many think higher temperatures should make the glaze flow more freely, but often it actually makes the pinhole or healing problem worse. Just counter intuitive so it’s good to be aware of and use in your tool chest of possible solutions. Incidentally I have never cured pinholes with a higher temp for longer. Doesn’t mean anything, just never has worked for me and most often made things worse.

[thiamant]

On 3/22/2021 at 11:21 AM, Bill Kielb said:

60c per hour is generally a good speed from the middle column of the Orton cone chart.  The rule right on the chart is the last segment at 60c per hour in about the last 100c of the firing. So cone 9 for you is 1260 minus 100c means the last segment starts at 1160c and fires at 60c per hour to 1260c. This should get your cone 9 cone to bend fairly close to the predicted. From there you added a 30 minute hold to get your heatwork close to cone 10 I believe,  and a drop and hold to try would be drop 100c and hold at 1160c for 20-30 minutes.

The concept is the fired surface tension of a particular glaze is too high at peak temperature for the glaze to heal so dropping some amount and holding or soaking gets the glaze to a point that it still flows but now heals as the surface tension reduces. Finding the best drop and best hold time takes some experimentation for a particular glaze.

Some folks just use it for most of their glazes to avoid issues with a particular glaze. I think @Hulk detailed his earlier in this thread and digital fire has a generic one or two. Folks usually develop what works best for them, their glaze, and their firing temperature by trial, improvement and more trial,  so a standard one likely does not exist.

Intuitively many think higher temperatures should make the glaze flow more freely, but often it actually makes the pinhole or healing problem worse. Just counter intuitive so it’s good to be aware of and use in your tool chest of possible solutions. Incidentally I have never cured pinholes with a higher temp for longer. Doesn’t mean anything, just never has worked for me and most often made things worse.

I see. I'm trying to design a new firing schedule, but I have to speed up the firing at some point because otherwise the total time will exceed 11 hours and I think it was already too much... 

[Bill Kielb]

1 hour ago, thiamant said:

I see. I'm trying to design a new firing schedule, but I have to speed up the firing at some point because otherwise the total time will exceed 11 hours and I think it was already too much... 

Ok something like:

65c per hr to 120c              (~1.5 hrs)         Dry out slowly

275 c per hr to 1160c        (~3.8 hrs)         Midfire to 100c less than cone

60c per hr to 1260c            (~ 1.6 hrs)        Final segment to maturity

                                                          (~ 7 hrs)           Prox. Total fire time without soaks and holds

Your 30 minute hold at 1260c to get to cone 10                      Your soak to get to the next cone

drop 100c degrees and hold at 1160c for 20 minutes          Drop and hold that works for you (trial and error part)

If that’s not fast enough add some speed to your midfire segment say 300c per hour to trim 1/2 to 1 hour.

your final segment, your thirty minute soak to go to the next cone, and any drop and hold likely will amount to about three hours so that’s going to be about 25-35% of your total time. How much time is too much?

 

[thiamant]

Up to 10 hours would be fine I guess, Maybe that midfire segment is a bit too fast? 

What about this?

100C/h to 200c (~2h)

200C/h to 1160 C/h 

60 C /h to 1260 C /h

30 min hold at 1260

STEP down to 1160

20 min hold at 1160

total time ~9h

[Bill Kielb]

2 hours ago, thiamant said:

Up to 10 hours would be fine I guess, Maybe that midfire segment is a bit too fast? 

Seems fine to try in my view. It’s interesting to see what is perceived as too fast or too slow. You clay, construction and glaze outcome will really determine that. Production tile goes from room temp to cone 10 and back in hours. Clay is pretty tough, I don’t think I have fired to cone 10 in a gas kiln in more than 9 hours actually and average probably 8 hours. Our midfire segment can go up to 570f, or 300c per hour without issue so not I am sure how fast is fast these days.

[thiamant]

You are absolutely right, however my electric kiln might suffer a bit so I dont want to push it too hard. Just to extend its life as much as possible. If I was only considering the clay I would go all the way for sure, its also more convenient to have faster firings...

[Bill Kielb]

2 hours ago, thiamant said:

dont want to push it too hard. Just to extend its life as much as possible.

That’s an interesting point. Peak temperature definitely forms new cracks in the oxide of the elements and seems to be the most influential in element life. Time to fire has some effect and the longer you fire the longer shell losses or standby losses will actually increase the overall on time of the elements and the energy use by some fraction. Firing faster at lower temps could actually be slightly less wear.

Cone six definitely way better than cone ten  in this regard though if you can find a suitable claybody.

[Mark C.]

I use oribe  in a cone 10 reduction firing every few weeks. It can pinhole but its not much of an issue as its only occasionally a problem.

Now my fires are slow at the top end  temps which lays bubbles down and its slow cool as well.

Custar feldspar    -29.3

Silica 325 mesh.    -24.

whiting                       -21.2

talc-I use serria lite  -7.4

EPK                               -11.9

Bone ash.                  -1.0

Black copper oxide -5.2

This goes on just a bit thick and can run if to thick

-I use white glaze as an overglaze 

[Callie Beller Diesel]

1 hour ago, Mark C. said:

use oribe

This is the same recipe I posted, except you’re use black copper, rather than the green.

 

[shawnhar]

My green glaze gets those blisters if it is too thin. I added some epsom salt solution to my glaze and the blisters went away.

[Callie Beller Diesel]

If you add epsom salt to a glaze with bone ash in it, you’re going to get a gelled mess. It’s worse than Gerstley Borate for that.

[shawnhar]

Yikes! Strike my comment from the record.

[Callie Beller Diesel]

It’s not really common as a glaze ingredient. There’s limited reasons to use it, outside of bone china.  It’s not used in glazes below cone ten, because there’s other ways to get colloidal iridescent effects that are more user friendly. 

[neilestrick]

5 hours ago, Callie Beller Diesel said:

It’s not used in glazes below cone ten

It's used in iron red glazes for the phosphorous.

[neilestrick]

6 hours ago, Callie Beller Diesel said:

If you add epsom salt to a glaze with bone ash in it, you’re going to get a gelled mess.

I've never experienced this. Is it only true for real bone ash, not synthetic?

[Callie Beller Diesel]

@neilestrickI’ve only used the synthetic stuff to my knowledge. There’s a noticeable effect in the bucket. I understand the real stuff is more pronounced.

 

[neilestrick]

1 hour ago, Callie Beller Diesel said:

@neilestrickI’ve only used the synthetic stuff to my knowledge. There’s a noticeable effect in the bucket. I understand the real stuff is more pronounced.

 

Maybe I've just never used epsom salt in my iron reds. They tend to stay suspended pretty well. I'll pay closer attention next time I mix a batch.

[Callie Beller Diesel]

1 hour ago, neilestrick said:

They tend to stay suspended pretty well.

Exactly!

Edited to add:

1% in a glaze really does make sure you don’t have to worry about anything resembling hardpanning. I have the remains of a batch of that oribe that I haven’t used in 5 or more years, since I switched to cone 6. It’s still easily stirred.

I think it’s when you get into larger percentages like 5% it can play havoc.

[thiamant]

On 3/29/2021 at 3:46 AM, Mark C. said:

I use oribe  in a cone 10 reduction firing every few weeks. It can pinhole but its not much of an issue as its only occasionally a problem.

Now my fires are slow at the top end  temps which lays bubbles down and its slow cool as well.

Custar feldspar    -29.3

Silica 325 mesh.    -24.

whiting                       -21.2

talc-I use serria lite  -7.4

EPK                               -11.9

Bone ash.                  -1.0

Black copper oxide -5.2

This goes on just a bit thick and can run if to thick

-I use white glaze as an overglaze 

 

On 3/29/2021 at 5:08 AM, Callie Beller Diesel said:

This is the same recipe I posted, except you’re use black copper, rather than the green.

 

Have you tried adding 1% RIO to obtain a hint of red/brownish color on the edges?

[Mark C.]

I have had my bag of bone ash forever (maybe 35 years) and I'm sure its not synthetic . I do not use Epson salts in it as it stays floating just fine-the glaze is always a bit thick anyway.

Never added iron to it. It can turn red on its own in spots

[Callie Beller Diesel]

1 hour ago, thiamant said:

Have you tried adding 1% RIO to obtain a hint of red/brownish color on the edges?

I did not, no. Here’s an image of a piece I made almost a decade ago. It’s on a very white stoneware. The glaze surrounding it is a shino. If you notice, the shino did pick up some flashing from the oribe. Perhaps if you tried it on a less clean stoneware, the effect would be more pronounced. 
 

edited to add photo. 

[Callie Beller Diesel]

I’m later to the game than Mark is, so my bone ash is likely synthetic. Adding epsom salt is very unnecessary for this glaze. It suspend all by itself.

[thiamant]

Just got the new test out of the kiln. New body, drop and soak firing to cone 9.

Less pinholes but still got some. There are plenty of them on the inside of the pot. 

I guess I will just discard this glaze. I was overconfident and made a whole bucket of it. Damn.

[neilestrick]

Start adding equal parts silica and koalin in 2% increments. It may just need a little stabilizing since these high copper glazes are often over-fluxed. At some point it will mess up the look of the glaze, but it may stabilize it before that happens. It's worth a try before you toss it. You'll have to estimate the % based on your original batch, but you can pull out a cup or two at a time for testing and math it out for the whole batch.