search  current discussion  categories  glazes - cone 04-06 

low fire glaze failed the vinegar test

updated tue 23 may 00


Rachael Rice on sun 21 may 00

We had been experimenting with low fire glazes at school this semester.
I turned several white earthenware bowls which I experimented with many
different combinations of commercial undergalzes & glazes . A few of my
bowls came out beautiful but I didn't trust their food safety so I put
vinegar in them and found that after just several hours they had a white
ring around them and the beautifulness of the bottom was gone.
Do I assume this is not a combination I can use on functional pottery?
Here is what I did. I painted apple green underglaze on the bowl and
then dipped it in a commercial Campbell's turquoise and royal blue
glaze. I dipped the rim in Campbell's gloss black glaze. Then I dipped
the bowl in a low fire copper matte glaze that a teacher mixed up.
Here's the formula:

Gerstely Borate 380 grams
Lithium 100 grams
NepSy 50 grams
Silica 420 grams
EPK 50 grams
Cu 20 grams

It was fired to cone 04. We used this matte alone on bowls and found
that oils from food stained the surface and decided if we put it on over
a commercial gloss or majolica it sealed it better. Any advise would be