Expert: Leisha Hiester - 6/29/2008

Question
QUESTION: Sorry to keep asking, but if it was a miss match of glaze and clay then would you get some pieces coming out o.k? She said that she had started adding something to the earthenware to keep it smoother for longer. potash? something like that. She had wondered it this was a problem. As I sell my work I'm desperate to find the answer. But as she is very helpful I don't want to ask her about too much she is just as puzzled as I am so I would think that she would have made sure that she was doing the right thing. It is a earthen ware glaze. She must be overlooking something though.
As the crazing comes from the sides could it be that the glaze applied to the e sides of the piece is causing a build up and therefore over glazing? I use one coat just along that strip so effectively a small strip of three coats would occur. But unsure why the 3 fire would fix this problem.

cheers
thanks for the kind words about my pendant

ANSWER: Kerry,
No problem, I enjoy figuring out a problem and helping in any way I can. Is she making her own clay? That may explain some. If you're sure you're using earthenware glaze, make sure she's making/using an earthenware clay.
Usually, if you've applied too much clear glaze it will bubble versus crackle.
Leisha

---------- FOLLOW-UP ----------

QUESTION: No I think she buys slip in for pouring her molds and then adds the potash or something like that to keep it a smooth runny consistency for longer.

I didn't mention this but also in the last lot that was fired with the gare glaze I ended up with a few raised bumps like that from a stilt but finer on some of my pieces, any idea?

I'm beginning to think that it must be under firing problem as that is the only reason I can think of why when the crazing appears you can fire it again and the crazing goes away. Its a tile from a mold that I'm using instead of pieces of stretched(?) clay. I'm going to see what happens with the higher firing and if still no joy will ask you a few more questions if that's o.k

cheers thanks for the help

Answer
Kerry,
She may be over flocculating the slip. That is hard to correct. Do you know if she uses a hydrometer and viscometer? She should also be checking for uniformity by testing for set up time and pour out times of the molds. If you pour a piece and cut it in half the thickness should be the same at the top and bottom. There's a lot more to pouring molds than many realize to get it right. If you're selling your work, you may want to purchase your own to get it right eventually.

No problem, ask away. I'll enjoy knowing you got this corrected.

Leisha