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Pin-Holing In Standard 112, But Not B-Mix - Help And Opinions!?

pinholing 112 bmix

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#1 grype

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Posted 13 July 2014 - 04:14 PM

I am having an issue with standard 112 brownspec. I have been using the clay for about a month now and I have fired 3 kiln loads, each time changing my firing process by 1 or 2 steps. So far I have been unable to solve the pinholing problem in this clay body.

 

Firing 1. Bisque to ^06 / Glaze to ^6, top peephole out till 1500F then plugged in both bisque and glaze firing. - Had several pinholes on the 112 body, but none in the bmix body.

 

Firing 2. Bisque to ^05 / Glaze to ^6 (held 5 minutes), top peephole out till 1800 then plugged in both bisque and glaze firing. - Had same pinholing on the 112 body but again none in the bmix body.

 

Firing 3. Bisque to ^04 / Glaze to ^6 (held 5 minutes), top peephole out the entire time and then plugged after kiln completed. - Still the same pinholing on the 112 but again none in the bmix body.

 

I love the way 112 looks in the ^6 finished product. I am making some bowls where I only glaze the inside of the bowl and I love the beautiful color and speckles on the outside of the bowl. However I cannot for the life of me get rid of pin holing. 

 

I have read a lot of the threads about pinholing and most people say it has to do with the bisque firing, so some more details about my bisque. I do not stack anything inside of the bisque. I know this is less efficient but I wanted to start out with less and stack more if my first firing came out great. Since it hasn't I haven't increased my load. I use the same exact load in the bisque as I do the glaze firing so plenty of room for gasses to get out.

 

After bisque cools I take out all the pieces and wipe them with a damp sponge. I let them dry about 1 hour after wiping, then I proceed to brush on glaze while waiting an hour between each coat for the glaze to dry. I wait for the glazes to dry completely about 4-5 hours then I glaze fire.

 

In my final product it seems most of the pinholing is inside of a speckle. Is this a common place for a manganese speckled clay? Or am I just using glazes that really don't fit my clay body well? 

 

Here are some pictures showing a few of the pinholes, most of them are inside of the speckle:

 

Attached File  WP_20140713_002.jpg   44.9KB   3 downloads

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Attached File  WP_20140713_004.jpg   44.76KB   0 downloads

Attached File  WP_20140713_005.jpg   51.62KB   0 downloads

 

I really like the speckled clay a lot, but I am debating on changing to a different clay.

 

I am thinking about Highwaters Little Loafers or Red Stone. I thought about Red Rock, but it has speckles added so I am not sure if want to go through the same thing.

 

My plan for this coming up week is to by 25 lbs of Little Loafers, Red Stone, Red Rock, and Brown Stone. Then throw a cylinder, a bowl, and a small plate in each clay and apply the same glaze to each one and then bisque to ^05, glaze to ^6 (5 minute hold). 

 

Does this seem like the thing to do?

 

I know 112 is a super popular clay, so I can't imagine I am the only person having this problem, yet I can't seem to find other people having issues with 112! Any help or ideas would be appreciated, my kiln is pretty small so I can test stuff very fast. I already have a lot of pieces ready for the next round of testing that are bone dry sitting on the shelves.

 

Edit: After a much closer look at my first load vs my 3rd the pinholing is definitely less prevalent than in the first firing. So I am on the right path to fixing the solution but I just haven't gotten there yet. 



#2 Wyndham

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Posted 13 July 2014 - 04:35 PM

There have been post about the goldart clay used in some of the different brownstone clay bodies. It seem that some may have more organics/coal particles in the clay than it used to. This may or may not be true. One idea is to create a bisk firing schedule that allows longer burnout time in the 1100 deg f to 1600 or 1700 degrees range.

You might look at your kiln controller manual and find what the bisk schedule is and make one with longer firing times between these 2 temperature areas.

If the program calls for 200 deg/hr in this area, make a custom ramp/hold that slows it down to maybe 100 deg/hr.

I'm sure others here may have a better heat ramp suggestion than I.

Just a few ideas

Wyndham



#3 grype

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Posted 13 July 2014 - 04:41 PM

That is a good idea I haven't thought about trying that yet. Thanks.

 

Here is what my kiln is currently doing :  http://hotkilns.com/easy-fire-programs

 

I think I might try a slow bisque to 06 instead of a fast bisque to 04. I don't think the final temperature is making much difference compared to the speed of the bisque after looking at the charts. There is a drastic difference between a slow bisque to 06 and a fast bisque to 04 in the times between the crucial burn off periods.



#4 JBaymore

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Posted 13 July 2014 - 04:58 PM

Do you have a local pickup ventilation unit running on that electric bisque kiln?

 

best,

 

...................john


John Baymore
Immediate Past President; Potters Council
Professor of Ceramics; New Hampshire Insitute of Art

http://www.JohnBaymore.com

#5 grype

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Posted 13 July 2014 - 05:03 PM

Do you have a local pickup ventilation unit running on that electric bisque kiln?

 

best,

 

...................john

 

I do not have any type of vent kit installed. I just fire with the top peephole out (kiln is 2 sections). I am kinda regretting not getting a vent kit now and I might purchase one in the future.



#6 JBaymore

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Posted 13 July 2014 - 05:51 PM

That's where I'd start...... for more than just this pinholing reason.

 

best,

 

...................john


John Baymore
Immediate Past President; Potters Council
Professor of Ceramics; New Hampshire Insitute of Art

http://www.JohnBaymore.com

#7 grype

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Posted 13 July 2014 - 06:46 PM

That's where I'd start...... for more than just this pinholing reason.

 

best,

 

...................john

 

I guess that I will get one, you think it will be the answer to this particular problem and prevent others from happening in the future?



#8 JBaymore

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Posted 13 July 2014 - 06:50 PM

The "classic" issue of pinholing is from materials that require oxygen not getting oxidized during the bisque firing. Without active local pickup vents.... even with spy holes open...... there is poor circulation of air within the chamber .

 

That being said.... diagnosing the issue from afar with limited information and no chance to see all of the pieces in person..... it isw hard to say if it is a "classic" case or not.

 

Generally, dark bodies have more carbonaceous material than white bodies... so the fact that the BMix is fine and the darker clay is not is one "clue".

 

best,

 

...................john


John Baymore
Immediate Past President; Potters Council
Professor of Ceramics; New Hampshire Insitute of Art

http://www.JohnBaymore.com

#9 grype

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Posted 13 July 2014 - 07:59 PM

John,

 

Thanks so much for your help. I think I am just going to move to a less carbonaceous clay body until I get a vent kit installed. 



#10 grype

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Posted 13 July 2014 - 08:09 PM

Looking at these vent systems, I have my kiln in my garage I wonder if it will be ok to just mount the fan onto the wall and then run another pipe out to the garage door, so when I am running it I just put that pipe outside the door.

 

Edit: Looking at the vent blueprints, there really isn't much to a vent. I think I could probably build something like this myself for much cheaper than 400 dollars for the kit. 



#11 grype

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Posted 13 July 2014 - 08:49 PM

I found this: http://www.hotkilns....re-instruct.pdf. My brother is a welder, so I am just gonna fabricate this basically myself for much cheaper.

 

Thanks for all your help John and others. Can't wait to figure this out.

 

I just need to fabricate a box for the bottom based off the ventsure diagram and I found the same type of blower if not the exact one. It has the exact same specs:

 

http://www.northland...TDP7_p_907.html

 

Wooo! I will post results here after I finish building this thing this week.



#12 oldlady

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Posted 15 July 2014 - 11:49 PM

standard ceramics will help you with the pinhole problem.  they replaced 16 boxes of 112 for me years ago when the tiny specks came out of the bag as large blobs instead.  it is in their interest that you are satisfied.  ask them for help.


"putting you down does not raise me up."

#13 grype

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Posted 18 July 2014 - 07:34 PM

Well I built my vent kit for $180 partially homemade. I read the manual for the L&L one and kinda did the same thing but with what fits my situation. I bought the L&L box that goes on the bottom, then bought an inline fan instead of the squirrel box fan. I mounted the fan on 2x10 on the floor then ran venting out the garage door. I pull it back in when its not running. I drilled the 1/4 inch hole in the bottom of the kiln and checked it with the fan on, it definitely is sucking air down. I am pretty excited, going to do a bisque firing tomorrow and then a glaze firing right after. I will update with details and hopefully no pin holes! 

 

Does anyone have any recommendations on how much to leave the L&L vent box hole open. I read in the manual it says start at 1/2 and adjust. My fan is a little bit stronger than the fan that comes with the L&L kit, so I think I am gonna start with 1/2-3/4 open. I don't wan't to suck to much air out of the kiln right?

 

Fun stuff! 



#14 neilestrick

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Posted 18 July 2014 - 09:21 PM

 

 

Does anyone have any recommendations on how much to leave the L&L vent box hole open. I read in the manual it says start at 1/2 and adjust. My fan is a little bit stronger than the fan that comes with the L&L kit, so I think I am gonna start with 1/2-3/4 open. I don't wan't to suck to much air out of the kiln right?

 

Fun stuff! 

 

Start up the fan with the kiln closed and hold a smoking match at a gap in the lid, or if you drilled a hole in the lid, next to the hole. Adjust the damper on the collection box to where it sucks the smoke in. Test again during a firing if the lid gap opens up.


Neil Estrick
Kiln Repair Tech
L&L Kilns Distributor
Owner, Neil Estrick Gallery, LLC
www.neilestrickgallery.com

neil@neilestrickgallery.com


#15 grype

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Posted 18 July 2014 - 09:35 PM

Neil, thanks. I didn't drill a hole in the lid because there is plenty of room around the lid for air to get in. I will do this right now, thanks for tip.



#16 grype

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Posted 18 July 2014 - 09:41 PM

I just tested. It didn't seem to pull a lot, but a little amount went in when the box was closed the nearly entire way. Maybe my kiln is sealed tighter than I thought. 

 

EDIT: I went back and lit some paper so that the smoke would last longer. I went around the kiln till I found a place where it went in for sure.

 

I found that once I moved the collection box anywhere past halfway it stops sucking in. So I left it at the point right where it starts sucking the smoke in. Thanks for your help. 



#17 grype

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Posted 31 July 2014 - 05:48 AM

Well I think I finally have a batch of pots with little to no pinholes. I can't be certain yet. Kiln is at 600F. I looked through the peepholes with a flashlight, glazes look glassy with no visible pinholes so far. I think the combination of a new clay + slowly increasing the vent kit's air flow through the kiln solved the issue. This was my 3rd glaze firing since installing the kit, each time I increased(closed) the vent box slightly.

 

I will post results tonight when I get to open the thing! I'm dancing in my garage! Thanks for the help folks.

 

If it is 100% fixed I will post my changes, and firing info.



#18 grype

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Posted 31 July 2014 - 05:46 PM

Well, pots came out with less pinholes, but still some there. I held the kiln for 10 minutes, which made the pots that were red rock clay have boils in it. So obviously it got to hot for that clay body. The little loafers did superb with 0 pinholing. The brown speckle did well, but had minor pinholing. I think I am putting my glazes on too thick. Going to try a thinner glaze application soon. I am also just going to switch to the white body for now. I want to get some good results to boost my morale and then maybe I will revisit the colored clays again. 







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