Jump to content

Recommended Posts

I fired 20 4"x4" raku tiles today and all but 4 broke either during the firing or as soon as they were removed from the kiln. I did fire them propped vertically on ceramic brick so I could remove them with tongs. They were hand built tiles with leaf impressions using Standard Ceramics 239 Raku clay. They  cracked in half or close to in half. What caused them to crack? (I have been doing raku firings for 40 years).

Diane

Edited by Diane Pontoriero
provide more info

Share this post


Link to post
Share on other sites

The tiles were 1/4" thick and roughly 4"x4" square. They were bisque fired to cone04. We had been raku firing for about 3 hours when the tiles were ready to go in the kiln. I warm them on the top of my Olympic Raku Kiln before putting them in. Then slowly increase the temp in the kiln. By that time the pieces were maturing in 20-30 minutes. I use Standard Ceramics 239 raku clay. I am thinking that by resting them vertically on the hot fire brick caused stress and they cracked. May have to fire them flat and figure out how to pick them up.

Diane

Share this post


Link to post
Share on other sites
3 hours ago, Diane Pontoriero said:

The tiles were 1/4" thick and roughly 4"x4" square. They were bisque fired to cone04. We had been raku firing for about 3 hours when the tiles were ready to go in the kiln. I warm them on the top of my Olympic Raku Kiln before putting them in. Then slowly increase the temp in the kiln. By that time the pieces were maturing in 20-30 minutes. I use Standard Ceramics 239 raku clay. I am thinking that by resting them vertically on the hot fire brick caused stress and they cracked. May have to fire them flat and figure out how to pick them up.

Diane

Done in 20 to 30 minutes is 3600 - 5400  degrees per hour. You might want to try slowing it down a bit and see if you can still leave them vertically stacked. Even with normal wares if I make temp in 20 minutes some things seem to crack more than if I slow things up a bit. Might be worth a try for the tiles.

Share this post


Link to post
Share on other sites

When you say "resting ... on the fire brick," are you using soft IFB brick or hard brick as the support? I used to put a cool shard of broken kiln shelf (of which I have a whole bucket, just for this purpose) on the hot shelf before loading each piece of ware on it to alleviate the initial thermal shock. Then I "discovered" setting an IFB brick on the shelf and loading the ware on it - don't have to swap out the brick for each new piece despite it looking like it is red hot.  When I have a leaning piece such as yours, I set another IFB brick on edge to lean against. Now most of my breakage is due to poor construction of the joints, not body.

Share this post


Link to post
Share on other sites

Yes, I am using soft IFB brick. I will definitely try your suggestion and slow down the firing. I will also have my student have her tiles ready for the first couple of loads so I can heat them up slowly. Thank you. I will report on our next firing. I agree up until these tiles, the only breakage would be construction issues.

Share this post


Link to post
Share on other sites

My bet is that you are putting the tiles on hot brick, and the thermal shock is what is cracking them during firing. Try using cold brick to rest the tile on and see if that helps.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.