Dan Saultman on wed 24 oct 07
My previous posting asking for help eliminating a slight milkiness in a
04 clear glaze (when applied thickly) has only resulted in 2 replies.
So, I will try again...
I need the application to be thick (it's for a shower enclosure). So
applying thinner is not an option. A long soak is not an option since I
fire these pieces with my regular bisque firing. It is being sprayed
on.
The glaze is almost there. It just needs a little tweaking. I have a
hunch that the milkiness comes from the EPK in the recipe. The other
components are frits and flint. So I will cut back on the EPK in one of
my tests.
This seems to be a common problem with 04 and cone 6 clear glazes.
Surely someone has worked this problem out.
My 04 recipe is:
Frit (Ferro) 3134....................42.4
Frit (Ferro) 3195....................42.4
Flint......................................6.5
EPK (Kaolin) ........................8.7
........................................100.00
add colorants and stains at 3.3
for saturated colors.
Thank you
Dan
Dan Saultman
Fine-Art Pottery
Detroit
http://www.saultman.com
May Luk on wed 24 oct 07
Hello Dan;
Although impossible to say with certainty without close examination, it is possble that the thick glaze is just full of tiny entrapped bubbles. At any rate, a quick fix is low sol lead frit. If lead oxide makes you nervous, you can find other strategy to get rid of this glaze fault in Ceramic Science for the Potter by W.G. Lawrence and R.R. West (Chapter 11) and Understanding Glazes by Eppler and Obstler (Chapter 15). I can fax you the pages if you are keen.
Regards
May
Kings County
Ivor and Olive Lewis on thu 25 oct 07
Dear Dan Saultman,
I think your problem arises from the overburden of Boron Frit in your =
glaze. These bring with them a considerable mass of Boron which, in the =
form of Boric oxide, is a glass former.
Your recipe is deficient in Flint which is the foundation of the glass =
structure of pottery glazes.
By creating two glasses you will always get phase separation where two =
liquids are immiscible or mutually insoluble. This manifests itself as =
opacity. Migration of Silica from your clay body counteracts this when =
your glaze is applied thinly.
For a quick fix, tweaking if you like, I would line blend your dry glaze =
mixture with Silica omitting the end members. I would also do the same =
thing with Kaolin and Aluminium Hydrate just as a learning exercise.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
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