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chalky test tiles & iron?

updated sun 29 jun 03


clifton wood on sat 28 jun 03

hi, everyone.

well, i've built up a collection of duncon concepts underglazes.

and i was so proud of myself... decided to stop relying on the colors shown in the
booklet, and make some tiny text tiles for real, live color chips.

i made every tile the same, fired all to the same cone, included in stoneware bisque
firings. i fit into different firings, as i forced myself to complete them.

they all look fine - great colors, glossy surface, etc.


for the ones that just came out...

the colors look fine - but they are ALL non-glassy, almost chalky, but nothing rubs
off. very dry matte.

the only difference in the firings?

i had 3 toad houses, with fairly thick coatings of sieved native red clay from n

could the presence of this clay - maybe the iron? - account for this?


here's my real panicky question...

i can always redo these tiles if i feel it's really necessary.

but in the same firing were about 30 test cups. these are part of a group of 110
test cups for a cone 6 glaze project we are starting. the other 80 cups were fired

is there any chance that these test cups were affected in any way by whatever hit my
color chips?

or can i be reasonably confident that they won't perform any differently than the
other 80 cups, once they are glazed & fired to cone 10?

thanks so much for your help.

Snail Scott on sat 28 jun 03

At 06:20 AM 6/28/03 -0400, you wrote:
>...test tiles for real, live color chips...
>[last firing]...very dry matte.

Seems unlikely that the other items in the firing
are to blame. Try refiring the load. Do you use
witness cones? It sounds like that last load was
simply underfired.

I wouldn't worry too much about your bisqued test
cups, though. If they were indeed underfired, they
may soak up a little more glaze than the others,
but it probably won't greatly affect the outcome.
Refiring them with the test tiles might still be a
good idea, if you don't need the kiln space for
other stuff.