Fraley on wed 1 may 02
I've got this engobe that is giving me problems. Most times it works
fine but about 5% of the time it either has small patches that flake
off after a cone 04 bisque or has hair line cracks (made visible from an
oxide wash) that peel off during the cone 6 firing. The problem areas
are localized and like I said it works well most times but I want to get
rid of this 5% loss rate.
I apply the engobe at the leather hard stage but I've ran some tests on
almost bone dry clay to see if that would cause the flakes but it didn't
fail. I think I read about someone adding borax to help it adhere to the
clay body but I don't recall a percentage. Here are the details if
anyone can help.
Dense White Engobe (I think Alisa may have posted it) fired in oxidation
applied to Laguna's white cone 6 stoneware (#66 I think) at the leather
hard stage
Frit 3124 10%
Neph Sy. 20%
OM 4 Ball 30%
Zircopax 40%
The Zircopax is adjusted with oxides and stains for color variations.
Thanks for any help any of you may be able to give.
Toby Atticus Fraley
Ron Roy on tue 7 may 02
Hi Toby,
This slip has only 30% plastic material - the OM4 - if you check out your
clay body - measuring the shrinkage from leather hard to bone dry and
bisque - you can then adjust the shrinkage (measured in the same way) of
the slip and make adjustments to it.
There may also be an adhesion problem - the smoother the ware is the more
likely the slip will not be able to "grab" on. Perhaps roughing the surface
to be covered will do the trick.
I would also try adding a small amount of vinegar to the slip before
application - it seems to help stick clay together.
RR
>I've got this engobe that is giving me problems. Most times it works
>fine but about 5% of the time it either has small patches that flake
>off after a cone 04 bisque or has hair line cracks (made visible from an
>oxide wash) that peel off during the cone 6 firing. The problem areas
>are localized and like I said it works well most times but I want to get
>rid of this 5% loss rate.
>I apply the engobe at the leather hard stage but I've ran some tests on
>almost bone dry clay to see if that would cause the flakes but it didn't
>fail. I think I read about someone adding borax to help it adhere to the
>clay body but I don't recall a percentage. Here are the details if
>anyone can help.
>
>Dense White Engobe (I think Alisa may have posted it) fired in oxidation
>
>applied to Laguna's white cone 6 stoneware (#66 I think) at the leather
>hard stage
>
>Frit 3124 10%
>Neph Sy. 20%
>OM 4 Ball 30%
>Zircopax 40%
>
>The Zircopax is adjusted with oxides and stains for color variations.
>Thanks for any help any of you may be able to give.
>Toby Atticus Fraley
Ron Roy
RR #4
15084 Little Lake Road
Brighton
Ontario
Canada - K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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