Jump to content
  • Announcements

    • Jennifer Harnetty

      Moderators needed!   12/08/2017

      Ceramic Arts Network is looking for two new forum moderators for the Clay and Glaze Chemistry and Equipment Use and Repair sections of the Ceramic Arts Network Community Forum. We are looking for somebody who is an active participant (i.e. somebody who participates on a daily basis, or near daily) on the forum. Moderators must be willing to monitor the forum on a daily basis to remove spam, make sure members are adhering to the Forum Terms of Use, and make sure posts are in the appropriate categories. In addition to moderating their primary sections, Moderators must work as a team with other moderators to monitor the areas of the forum that do not have dedicated moderators (Educational Approaches and Resources, Aesthetic Approaches and Philosophy, etc.). Moderators must have a solid understanding of the area of the forum they are going to moderate (i.e. the Clay and Glaze Chemistry moderator must be somebody who mixes, tests, and has a decent understanding of materials). Moderators must be diplomatic communicators, be receptive to others’ ideas, and be able to see things from multiple perspectives. This is a volunteer position that comes with an honorary annual ICAN Gold membership. If you are interested, please send an email outlining your experience and qualifications to jharnetty@ceramics.org.
Sign in to follow this  
Dave K

Causes For Cracks

Recommended Posts

I have recently been making 8-9 pound pots. I am having a problem with the bottoms cracking. I think I am compressing the bottom correctly and getting any excess water out. The last two to crack seemed totally dry before bisque firing and I do a 3 hour preheat. I don't think the bottoms are overly thick or thin. One was starting to show a small crack before bisque firing and the other one nothing. Coming out of the bisque firing the were both cracked enough to see light through them. I am using stoneware. Does anyone have thoughts to what I am doing wrong?

 

Share this post


Link to post
Share on other sites

It's a thickness issue usually. If the bottom of the pot isn't close to the same thickness as the walls you'll get cracking. Also make sure the bottom is uniform thickness throughout. If the bottom on the inside curves upward, the bottom on the outside must also curve upward. Also make sure the wall near the bottom isn't too thick. All those variations can cause uneven drying and cracking.

D.M.Ernst likes this

Share this post


Link to post
Share on other sites

I use Standard 240. Neil, you are probably correct about the same thickness throughout. I am not use to throwing that much clay and am struggling in most aspects of it. I will have to keep trying and be more aware of the consistence of overall thickness. Thanks to everyone for the help.

Share this post


Link to post
Share on other sites

Before trimming, take a needle tool and measure the thickness of your bowl before trimming it. Measure it right in the center of the bottom, and in the area where you plan to establish a foot ring. Just knowing this in advance gives you a much better chance of getting even thickness when trimming. Don't worry, the act of trimming will seal up the needle holes. I have been throwing for 20+ years, and am now a full time professional, and I still do this when trimming large bowls.

florence w likes this

Share this post


Link to post
Share on other sites

Another way slightly different to get even bottom thickness is to make one of these depth measuring pin tools. Tap a sewing needle or pin into the bottom of a hardwood dowel, chopstick, paintbrush handle, whatever, then snip it off with side cutters to the depth you want the base. For wide items you use it in a few spots across the base. (this one is for a no trim base on wide pots, the needle is fine so it's kinda hard to see)


 


post-747-0-54919100-1474385880_thumb.jpg

post-747-0-54919100-1474385880_thumb.jpg

bciskepottery and Rae Reich like this

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×

Important Information

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