Laguna WC-391 B3 Brown Clay

[Norm Stuart]

Has anyone previously used Laguna WC-391 B-3 Brown Clay?

We bought one box to try out and the first person to use this clay made a slab construction of  about 3/8 inches thick.

This clay bloated in a Cone 6 firing, due to some part of the clay that is off-gassing.  The ware was previously bisque fired to Cone 04 and had a thin layer of clear glaze on it.

http://www.lagunaclay.com/clays/western/wc391.php

This clay is listed by Laguna as Cone 5, but I've never seen this problem in a Cone 5 clay fired to Cone 6.

[Norm Stuart]

You'd certainly hope a slow bisque to cure many problems later.

But many clays bloat, melt or experience other defects when fired hotter than their temperature range as the components of the clay decompose at these temperatures much hotter than bisque.. 

Unfortunately some batches of clay will also bloat when fired under their maximum temperature range due to raw material additions which don't meet specifications.

[Darthe Hues]

I watched this video on YouTube: http://youtu.be/tq7TdWkICZ0

The teacher said that doing a very slow bisque firing to higher temperature would take care of a lot of flaws that would come later in the glaze firing like pinholing, etc. because it allows more time for the gases to work their way to the surface. Especially with thicker pieces.

[Norm Stuart]

Thanks.  I'll try some WC-391 tiles myself when the rains stop.  I'll see if the bloating is from the thickness of his slabs or the Cone 6 firing.  It's not something I'd expect when bisquing to cone 04 with a 20 minute hold.

[Robert Coyle]

Just did some thin test tiles (1/4") . Looked OK but only fired to cone 5. Glazes seemed to strike in more than usual.