Ron Roy on tue 9 jun 09
Hi Sabra,
The first cracks to happen are called primary crazing - I read once that if
you could magnify the cracks enough you would see they are quite open - the=
n
- as the secondary crazing happens those wider cracks close up a bit - as
the tension is relieved.
The bigger the spaces between the cracks the easier it will be to cure the
crazing. If you decide to just add silica you will probably see an increase
in gloss - it's not the best way to cure crazing - subbing in lower
expansion oxides at the expense of the higher ones is a better way - you ca=
n
keep the silica/alumina ratio the same which helps to keep the texture of
the glaze the same.
Anyway it's quite easy to do with calculation software - send me a couple o=
f
the ones you like and tell me how fine the crazing is.
Even the primary crazing will turn to fine crazing with time by the way.
Shivering (glaze winds up too big for the clay) can sometimes resemble
crazing - look for spiral singe cracking and check sharp edges for fracture=
s
and missing glaze. Pouring hot water into a frozen pot (do it in the sink)
will show up glazes that are too "big" for the clay.
Anyone need an explanation of crazing and shivering let me know.
RR
On Sun, Jun 7, 2009 at 5:14 PM, nori wrote:
> Hi, everyone.
>
> i need help understanding crazing patterns.
>
> i'm testing a bunch of clear glazes, and they're crazing to varying
> degrees.
>
> i want to pick the one that is the best of the worst fit to work on.
>
> so...
>
> i read up on crazing in every book i have.... and found discussion about
> primary crazing & secondary crazing.
>
> seems that primary are the big, curving lines of craze.
> and secondary are the smaller lines that break it into tiny sections.
>
> so... would i be correct in assuming that a glaze with only primary
> craze lines is a better fit than one with lots of primary AND secondary?
>
> in other words, the bigger the areas of uncrazed glaze surface, the bette=
r?
>
> thanks in advance
>
> sabra
> --
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>
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--
Ron Roy
15084 Little Lake Road
Brighton, Ontario, Canada
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