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Cone 5 B-Mix


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#1 Laurie

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Posted 22 August 2013 - 02:54 PM

I am having problems with my cone 5 b-mix cracking wide open on all of my larger pieces.  I have kept them under plastic to slow drying, but to no avail. When I go back to uncover them, they are split wide open.  So disheartening. I have lost so many big pieces in the last couple of days. Does any one else make large thrown, or slab pieces, that have been having this problem too, and how do you remedy it? I have a ton of it that I need to use up. I do like how my glazes look on the b-mix is why I have tried working with it. Is there another clay that does not react this way that someone can recommend?  I also am having problems with the glaze crawling on some of the pieces, not all of them though.  I'm guessing that I am not getting all of the dust off after the bisque firing. Anyone else dealing with this?



#2 perkolator

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Posted 22 August 2013 - 04:51 PM

got a pic of how it's cracking?  like cracking from the lip?  i've used b-mix plenty of times, never really had any issues.  sounds like your issue could be due to a lack of compression or maybe oversaturation of the clay body when throwing.  hard to say without seeing where/how it's cracking.



#3 mregecko

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Posted 22 August 2013 - 06:29 PM

I have a long history, spanning many different studios and different batches of clay, with ungrogged B-Mix (Cone 5/6 and Cone10) cracking.

 

Never mattered how much I compressed my bottoms, how slowly I dried, etc.

 

I always had a huge problem with anything over ~8 inches cracking.

 

Bowls would crack in a half-moon where the foot meets the wall, with a radial crack up to the lip.

 

Platters would get S cracks that radiate to the edge of the foot.

 

I had to stop using it.



#4 OffCenter

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Posted 22 August 2013 - 06:41 PM

Along with other clays, I use B-Mix 5 (which is really a cone 6 clay), B-Mix 10, and B-Mix Woodfire and have not had problems with cracking. It is unlikely, but possible that both of you got a bad batch of B-Mix 5. Laguna sometimes screws up their clays. I got a bad batch of Frost 5 once and had to go to great extremes (adding a little paper) to fix it and warned lots of people away from Frost because of cracking only to discover when someone here pointed out to me that she had just made a complete dinner set out of Frost with no cracking problem, that I had bought a bad batch of Frost.

 

Jim


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#5 Laurie

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Posted 22 August 2013 - 07:13 PM

Thank you to everyone who replied.  Everything that is cracking of course, are large pieces. It is the tension between the sides of the platters and the bottoms of the platters. Everything that is cracking is over 10" wide. I don't have a problem with cracking with the tall, or small pieces that I make., only the large pieces.  The piece starts cracking almost as soon as they are taken off the bat., even if I cover them in plastic. The pieces crack whether it is thrown on the wheel, or rolled on the slab roller.  I might mention that I live in Colorado, where it is hot and dry. 



#6 Biglou13

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Posted 22 August 2013 - 07:22 PM

No. 5 Ball Clay 50.00
Silica 20.00
Feldspar 30.00

Found this supposed to be the recipe of b mix cone 10. I imagine the feldspar is upped to make it a cone 5/6.

I don't think a screw up in the recipe will make it any more or less prone to cracking. While drying.

If it is a bad batch what could have gone wrong to make it bad? What would make a clay more prone to cracking while drying.

Laurie pictures will help.
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#7 bciskepottery

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Posted 22 August 2013 - 07:35 PM

Try placing the wares to dry on a sheet of newsprint or plastic . . . something that will allow the ware to move while shrinking and not get snagged on the surface of a ware board. Also, watch for differences in the thickness of the wares -- thinner walls/sides vs. thicker bottoms or bases . . . that will cause uneven shrinking.

#8 Laurie

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Posted 22 August 2013 - 08:04 PM

Percolater and biglou13, the cracks are wide usually, and pretty much straight across the whole bottom of the pot. That is on the ones that I have thrown.  The slab platters, most generally just split along the edges.  I know that the edges are drying faster than the bottoms, causing tension. It happens sometimes so soon after I have made them, sometimes taking several days, whether the pot is covered with plastic or not. I just have to learn a way to keep that from happening. I think to take them off the bat asap and flip them over would help, but some of my big bowls and platters have handles, which doesn't make that so easy. Thanks for your help.



#9 Laurie

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Posted 22 August 2013 - 08:17 PM

Try placing the wares to dry on a sheet of newsprint or plastic . . . something that will allow the ware to move while shrinking and not get snagged on the surface of a ware board. Also, watch for differences in the thickness of the wares -- thinner walls/sides vs. thicker bottoms or bases . . . that will cause uneven shrinking.

Thank you for your input. I am going to try that.  Also, I am wondering about throwing on plaster bats.  Do you have info on making plaster bats?  My guess is that the pot will come off of it earlier, and then I would be able set it on the plastic sooner.  I have already lost over $1000.00 worth of pots in the last day or so, I need to figure this out soon. I have been careful about the thicknesses, for sure.



#10 Laurie

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Posted 22 August 2013 - 08:21 PM

got a pic of how it's cracking?  like cracking from the lip?  i've used b-mix plenty of times, never really had any issues.  sounds like your issue could be due to a lack of compression or maybe oversaturation of the clay body when throwing.  hard to say without seeing where/how it's cracking.

It's not cracking from the lip. It's cracking from one side of the pot, on the bottom, all the way across to the other side., and it happens on slab pieces too.



#11 Mark C.

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Posted 22 August 2013 - 09:07 PM

I knew a potter who made his living with b-mix cone 10- for about 20 years.  He worked about 12 tons a year during this period.It is really prone to cracking and he fought large forms cracking for many years until he went out of business ( from other issues)

I use about 500 #s of B-mix over about a 5-7 year period-mostly for large vases and super tall pots (market is really slow for them now)

I am a porcelain  production potter mostly now (except for salt pots)

I gave up large flat forms with it in the 80's-

I suggest only using it for smaller work which you have zero trouble with-why fight it?

B-mix dries super uneven (lips) so you need to even it out.

Bad batches come and go with all clay makers and I doubt thats the issue-Can you tell from the numbers on boxes to see if there are several different  batches involved?? You can call John Pacinni at laguna west with the box numbers if you really want to know about bad batches. Many potters do not pay attention to these box numbers ( or even seee them) but they are the only tracking you can do. I know which ton I'm on by them and which is the oldest clay in shed by them to use it 1st.

When you buy in many tons at a time you learn that the numbers make sense in even tons and old to newer clay as the numbers increase.

This body has always been a cracker on large flat forms-platters-baking dishes etc--common stuff for us in the business-Try a better body witch can hold up to flat stuff stress.

I use a body from Laguna for flat slab work called Half and half WC382 cone 10. it can be streched pulled twisted and handled with no cracking-its half Daves porcelain and half WSO bullet prove-I do not throw it.They sell two kinds on this. one is finer tighter  with sand if I recall or finer grog?. I use the WC 382 almost like a porcelain body with a little grog

 

The most invincible clay I know is wso-its more like some non clay thing but it cannot be foiled by large flat or uneven drying-I do not like my glazes on it so thats my main issue with it as well. If I wanted to say make a 3x2 foot fish for the wall I use this WSO and have with zero issues.

I do not fire midrange so cone 6 users will have to add some of thier bodies to this list-life is short and crappy cracking issues is something you should not fight with as we old timers have moved thru it in our past. Try a new body

Mark


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#12 Biglou13

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Posted 23 August 2013 - 04:31 AM

Have you tried wedging in some grog/grit..?
Do,you live in arrid environment?
What has changed from when your pots were not cracking?
What surface are you drying your pots on?
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#13 Denice

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Posted 23 August 2013 - 10:58 AM

I'm about to start a new mural and was thinking about using B-Mix with fine grog but your giving me second thoughts on that.  I have try B-Mix before for handbuilding and hated it but I thought with the grog in it it might be strong enough for large tiles.  I think I'll buy a box of it and do some tests before I buy it for a large project. Denice



#14 Wyndham

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Posted 23 August 2013 - 11:44 AM

It seems to me at least, that the weight of the piece may well be causing the cut off separation to heal back over on the turned pieces. I would try running the cutoff wire under the piece several times to keep it from re-adhering to the bat. 

Several possible solutions, use plaster bats for the turning(you may already be doing this). On the slab try placing a sheet of newspaper on the bottom. One other thing to try on the slab is to lightly coat the form with cornstarch, this will help relieve the stress as it starts to dry.

Then again, this may not help, but worth a try.

I hope this helps

Wyndham

\

 

Edit:

on the multiple cut off passes, I would wait for some time to pass, 10 or 20 min just a guess before passing the cutoff wire again.



#15 Mark C.

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Posted 23 August 2013 - 02:42 PM

I have thicker cut off wires for larger forms-this keeps them from reattaching.

Mark


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#16 Roberta12

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Posted 23 August 2013 - 03:12 PM

Laurie, I have not been a fan of  cone 5/6 Laguna b-mix.  I also had problems with cracking, (thrown work).   I was convinced by a person who sells Aardvark clay to try their B-mix.  I have to say that I have not had the problems with that.  No cracking problems.  Just thought I would share that.   I live in Colorado also and there is now an Aardvark dealer on the western slope and I think a couple of places on the eastern slope that sell it.    For handbuilding I have become a fan of Laguna Whitestone and 1/2 and 1/2.  Both are nice to work with, little warping, very strong. 

 

Roberta



#17 Wyndham

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Posted 23 August 2013 - 03:37 PM

B mix is also thixotropic. I have had a bag of older bmix that any other clay would be too stiff to wedge and throw and bmix wedged beautifully. I threw well and held it's shape and did not s crack. Bmix will absorb water very quickly compared to other clays so throwing with less water helps. Also check your slab thickness, too thick can cause problems.

Do a test batch with several 8in x 10in slabs at different thicknesses to see if that's the issue.

Wyndham



#18 Laurie

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Posted 28 August 2013 - 10:12 PM

Try placing the wares to dry on a sheet of newsprint or plastic . . . something that will allow the ware to move while shrinking and not get snagged on the surface of a ware board. Also, watch for differences in the thickness of the wares -- thinner walls/sides vs. thicker bottoms or bases . . . that will cause uneven shrinking.

Thank you for your response. I will try putting my slab ware on some newsprint or plastic.  What I realized today, was that most of the problems were with large pieces thrown on the wheel, and then a handle added later.  I did have several large slab platters crack too, though, just not as bad as the other thrown pieces. I appreciate your help.



#19 Laurie

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Posted 28 August 2013 - 10:20 PM

B mix is also thixotropic. I have had a bag of older bmix that any other clay would be too stiff to wedge and throw and bmix wedged beautifully. I threw well and held it's shape and did not s crack. Bmix will absorb water very quickly compared to other clays so throwing with less water helps. Also check your slab thickness, too thick can cause problems.

Do a test batch with several 8in x 10in slabs at different thicknesses to see if that's the issue.

Wyndham

Thank you for your input.  That could very well be a large part of my problem, I have been throwing with too much water.  I didn't realize that it absorbed water like that.  I was trying to make my pots which were open baking casseroles a little thicker so that they would be better for baking in.  Guess that could have also been a downfall. Thank you for your time.



#20 Laurie

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Posted 28 August 2013 - 10:21 PM

I have thicker cut off wires for larger forms-this keeps them from reattaching.

Mark

Good idea! Thanks, I will try that also.  I usually use a real thin cut off wire.






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