Jump to content


Photo
- - - - -

What Made Plates Break?


  • Please log in to reply
14 replies to this topic

#1 Mark369

Mark369

    Advanced Member

  • Members
  • PipPipPip
  • 67 posts
  • LocationLouisville,Ky & Indiana

Posted 23 May 2014 - 03:19 PM

4 of 5 plates in 08 firing Broke ???  Why????  

 

Plates where purchased bisque, glazed with commercial 06 clear fired ok.

Color glaze and under glaze applied and re-fired to 08 and they broke!   Any clue???Attached File  IM002255.jpg   103.06KB   5 downloadsAttached File  IM002256.jpg   124.19KB   3 downloadsAttached File  IM002257.jpg   143.14KB   2 downloads


Everything tastes better with cat hair in it !

 

Curiosity may have killed the cat, but it died knowing something! :wacko:


#2 Mark369

Mark369

    Advanced Member

  • Members
  • PipPipPip
  • 67 posts
  • LocationLouisville,Ky & Indiana

Posted 23 May 2014 - 03:22 PM

Here is the fourth plate. Attached File  IM002258.jpg   136.77KB   2 downloads

 

The one that did not brake was the top plate in the kiln. 6 hours to fire. Let it cool 48hr.


Everything tastes better with cat hair in it !

 

Curiosity may have killed the cat, but it died knowing something! :wacko:


#3 Wyndham

Wyndham

    Advanced Member

  • Members
  • PipPipPip
  • 444 posts
  • LocationSeagrove NC

Posted 23 May 2014 - 03:41 PM

Refiring too quickly will crack/break/ screwup  pieces.

You've got too much heat too quickly and the fired piece can't relieve the stress the heat puts on the piece. There is a temp range between 900-1200 deg f that the glaze.glass and the claybody go through quarts inversion. This is the critical temp but there are other temps lower to consider.

Wide plates & uneven temp will also bust'em up

Long and slow 200 deg/hr to 900 deg then 100 deg/hr till 1200 then back t0o 200deg/ hr to end for refires and still you may loose some.

You don't know how the bisk was made or fired so there might also be issues there as well.

Chalk it up to learning.

Wyndham



#4 neilestrick

neilestrick

    Neil Estrick

  • Members
  • PipPipPip
  • 2,841 posts
  • LocationGrayslake, IL

Posted 23 May 2014 - 03:57 PM

Probably from refiring too quickly.


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

neil@neilestrickgallery.com


#5 Pres

Pres

    Retired Art Teacher

  • Moderators
  • 2,110 posts
  • LocationCentral, PA

Posted 23 May 2014 - 04:33 PM

The others have pretty much nailed it I believe. You need to slow your firing time down.

 

I did take a minute to edit your title so that the search engine would have an easier time with it in the future.

 

Best,

Preston


Simply retired teacher, not dead, living the dream. on and on and. . . . on. . . .                                                                                 http://picworkspottery.blogspot.com/


#6 Mark369

Mark369

    Advanced Member

  • Members
  • PipPipPip
  • 67 posts
  • LocationLouisville,Ky & Indiana

Posted 23 May 2014 - 05:18 PM

I will try again and slow the firing time way down. I will update next week when done.  Thanks  I figured it was a stress issue, but not sure what.  Makes sense now.  I will be making my own plates soon with a hump mold. 

  Tired of learning in this manner. But I guess it will stick with me more profoundly.


Everything tastes better with cat hair in it !

 

Curiosity may have killed the cat, but it died knowing something! :wacko:


#7 Babs

Babs

    Advanced Member

  • Members
  • PipPipPip
  • 1,159 posts

Posted 23 May 2014 - 05:33 PM

 

  Tired of learning in this manner. But I guess it will stick with me more profoundly.

There has been a lot written on firing schedules and the reasons for them. If you read up on these it would be a mere start only.... The kiln is a hard teacher, stuff up a little, change something and it will get you! Guys here who have been in the field for decades would be first to say there are no absolutes in this field .



#8 Mark C.

Mark C.

    Advanced Member

  • Members
  • PipPipPip
  • 3,119 posts
  • LocationNear Arcata Ca-redwood rain forest

Posted 23 May 2014 - 07:35 PM

(Tired of learning in this manner)

Well thats the way with ceramics-experience trumps all other forms

Making mistakes often is the only way other than taking some advanced courses and even then ceramics will bite you. Its a long curve no matter how you slice it. Its lasts your whole life-trust me on this one.

Mark


Mark Cortright
www.liscomhillpottery.com

#9 Mark369

Mark369

    Advanced Member

  • Members
  • PipPipPip
  • 67 posts
  • LocationLouisville,Ky & Indiana

Posted 28 May 2014 - 08:36 PM

Slowed 08 firing down to 11 hours and put plugs in peep holes when shut off to slow cooling down.

3 plates broke and a bowel cracked one plate make it.

 In looking at them I noticed the bowel cracked in the base and not on edges.

I think it is Dunting during cooling (sharp edged crack) from not being glazed the same on both sides.

Will try again next week and see if that corrects it.   This is getting costly time wise.


Everything tastes better with cat hair in it !

 

Curiosity may have killed the cat, but it died knowing something! :wacko:


#10 Min

Min

    Advanced Member

  • Members
  • PipPipPip
  • 596 posts
  • LocationCanada

Posted 28 May 2014 - 10:12 PM

I think you have a couple things going on here. So just to clarify, you use bought bisque, glaze fire to ^06, apply underglazes and (coloured) glazes and refire to ^08. You put the plugs in when the kiln shuts off.

 

From looking at the star pattern of cracks on 2 of the plates plus the chunks of rim cracking off my thought would be you have too thick a glaze layer plus the kiln is cooling to quickly resulting in dunts.

 

You didn't say how long your kiln takes to cool down to approx a couple hundred degrees? If you have a rapidly cooling kiln then a firing down program might be necessary through the inversion temp zones.

 

You can put the plugs in the kiln once it is around 1100 (orange glow). You don't need to wait until the firing is complete.

 

just my 2 cents worth



#11 oldlady

oldlady

    single firing an electric kiln to cone 6

  • Members
  • PipPipPip
  • 1,067 posts
  • Locationharpers ferry west va and pinellas park fl

Posted 28 May 2014 - 11:17 PM

dumb question..............why are you first glazing to 06 with a clear glaze at all?  why are you not just using underglaze and covering everything with clear and firing it together?

 

(I haven't done low fire work in 30 years so I do not know if this is normal today)


"putting you down does not raise me up."

#12 Babs

Babs

    Advanced Member

  • Members
  • PipPipPip
  • 1,159 posts

Posted 29 May 2014 - 12:33 AM

I'm with you on this one Old Lady, only ever fired the underglaze and glaze together unless underglaze applied to raw ware.

What do the edges of the broken ware look like? Sharp?

If they are coming thro fine with te commercial clear glaze, why not try the underglaze, glaze and then fire routine, still require a slow firing, at least till equivalent of approx  600 d.Centigrade

In a glaze firing I put bungs in after wax is burnt off...

Do you know the clay body they are made of?



#13 Mark369

Mark369

    Advanced Member

  • Members
  • PipPipPip
  • 67 posts
  • LocationLouisville,Ky & Indiana

Posted 29 May 2014 - 06:52 AM

The edges of cracks are sharp.  The Bisque ware is from China. Who knows how it is fired or what is in it. It is supposed to be a substitute until I can make some plates.

Putting the under glaze and design glaze  over clear is easier to correct mistakes in application than on raw bisque. Putting the clear glaze over red glaze was burning out the red on smaller items. Clear glaze is poured on. Kiln takes about 16 hr to cool down to touch ware. First time using under glazes. Have now read up on proper application.


Everything tastes better with cat hair in it !

 

Curiosity may have killed the cat, but it died knowing something! :wacko:


#14 Babs

Babs

    Advanced Member

  • Members
  • PipPipPip
  • 1,159 posts

Posted 29 May 2014 - 07:54 PM

Sorry thought the red was an underglaze. Could apply underglaze, fire to  06 to set then glaze for the first time and fire.

May have to consider firing down.

ANy manufacturing instructions for firing this ware?

Any local press molded stuff you could run a comparison to?

Could mention cheap imports :) but I wont :ph34r:



#15 alabama

alabama

    Advanced Member

  • Members
  • PipPipPip
  • 93 posts
  • LocationSlapout

Posted 30 May 2014 - 04:06 PM

Hey,

     It looks (in my limited experience in this) that the clay body of the Chinese plates just failed.  We had students throw cone 10 Amaco clay from

Hobby Lobby fail somewhat in this same manner.

     I've had some success going to Thrift shops, buying 25 cent white china plates, decorating them with cobalt cone 06 underglazing and firing to cone 06.

When things go right the underglaze fires to the bright shiny glaze its suppose to. 

     Plates and platters seem suicidal and look for a reason to crack. 

Hope this helps,

Alabama






0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users