please help!! no matter what i do, my mugs craze :( getting really defeated

[kt717]

hi!

i am using amaco white art clay 25. 

i underglaze, bisque to cone 04, then use amaco lg-10 clear transparent to make them food safe. then fire to cone 05.

what am i doing wrong? 

[Chilly]

Hello @kt717  Welcome to the forum.  You will probably get lots more questions as the majority of our members will be waking up soon.  In the meantime, here are a couple of questions to start:

 

3 hours ago, kt717 said:

amaco lg-10 clear

This advice is from a local (to me ) supplier

""Cone 05. AMACO Gloss Glazes fire to a smooth, glossy finish at a witness Cone 05 (1915°F, 1046°C). For best results, slow fire lead free glazes. Amaco Gloss Glazes flow slightly during firing to a high gloss finish, while correcting most application imperfections. Good results can be obtained on all AMACO ceramic clay or slip.
AMACO® Gloss Glazesare formulated for brushing application. They may also be adjusted to work in pouring, dipping, and sponging applications. They are available in liquid (pint or gallon) or one pound dry.
LG-10 is a clear, all-over covering glaze that produces a smooth, high gloss finish at a mature witness Cone 06 (1911°F, 1044°C). Two coats of LG-10 is usually sufficient to achieve a smooth glossy finish.""

 

Are you slow firing as above?.

3 hours ago, kt717 said:

then fire to cone 05.

Have you verified your firing by using cones.

[Bill Kielb]

I think I would call Amaco and ask about compatibility. The clay fires to cone 3 and the glaze to 05 so there is a significant difference when each matures. Crazing is a difference in the coefficients of fired expansion (COE). So are we to fire the clay to cone 3 then the glaze to 05 and they match better?

Generally a thick layer of glaze will highlight the mismatch so thin applications may help with immediate crazing. Fire slowly? Generally firing slow or medium will not affect the fired  COE and firing to maturity establishes repeatability. Amaco may have worked out a schedule with this clay and glaze that makes it work in the short term.

I Just  have no idea of slow, medium, fast, it’s a relative term, is 400 degrees per hour fast or slow? Bartlett uses this in their cone fire schedule as slow.

I think your best bet, call Amaco. I notice their test tiles do not appear to be done using this clay, I find that interesting. The normal advice would be find a different clear that has a COE that matches closer or change your clay if that is not possible. All need to be tested in the real world to see if they match though. There is still No substitute for testing first.

Absorption for this clay fired to 04 is listed at 13.7%, so to be waterproof and not weep the glaze must be in good shape. No crazing, no imperfections else the pot will likely weep. I suggest test it on a suitable surface first before ruining your finest wood.