David Hendley on wed 22 dec 99
Ingeborg , thanks a lot for these test results.
This is the kind of "in the trenches" work that is
required to really find out what is happening with
glazes.
The results from increasing the tin oxide are very
interesting. Has anyone else ever run line blends
of tin oxide in copper red glazes?
The results confirm my belief that a good copper
red glaze does not need to be crazed or runny.
The original Pete's Red is deficient in both alumina
and silica and has a very high expansion, and I would
suggest that the "revisions" are not revisions at all,
but are, in fact, "new" glazes. Shall we call them
"Ron's Cranberry Red"?
I hope you will put your tests in several firings of your
kiln to see if the results are consistent from firing
to firing. I will put some tests in my next couple
of firings to see what I get.
It can be very difficult to detect crazing in some glazes,
like alumina matts and copper reds, and I recommend
a 30X lighted magnifier for this. These things use a
single AA battery that lasts for years and are only about
$10 or so. Several years ago Radio Shack had them.
--
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com/
----------------------------Original message----------------------------
------------------
I have completed my first round of tests on the revision to Pete's
Cranberry.
The tests were performed on 4 different claybodies--all ^10. One was a gray
body, one white, and the other two a cream/buff. While there are
differences
between the clay bodies, the glaze results are surprisingly similar. My
report
to the list is only on the glaze test results. All of the samples were fired
to
^10 with propane in a reduction atmosphere.
Original Recipe
Pete's Cranberry Altered ^9,10,11 ( PCA186) R
a.. Custer Feldspar 74
b.. Gerstley Borate 10
c.. Whiting 11
d.. Flint 5
Add:
a.. Copper Carb .35
b.. Tin Ox 1.0
Very Red, True Cranberry color, Great depth, high gloss, breaks white on
rims
and ridges. Runs badly when thick. Crazes badly.
----------------------------------------------------------------------------
----
Ron Roy's Revision to Pete's Red ^9,10,11 ( RRRPR193) R
a.. Feldspar G-200 53
b.. Frit 3134 15
c.. Whiting 10
d.. EPK 10
e.. Silica 12
Add:
a.. Copper Carb .35
b.. Tin Ox 1.0
Results: Glossy, Less Fluid, color more brown than red, Not bright clear
as
original, no apparent crazing on upright test. Flat tile similar. Does not
break at rims
----------------------------------------------------------------------------
----
RRRPR193
Add:
a.. copper carb .35
b.. Tin OX 2.0
Results: Glossy, smooth bright red with darker flecks, no apparent crazing,
does not break at rims. Is fluid but probably OK. with care. Upright and
flat
tile are similar.
----------------------------------------------------------------------------
----
RRRPR193
Add:
a.. copper carb .35
b.. Tin OX 3.0
Results: Glossy , smooth, bright red with flecks, nice depth, does not
appear
to break at rims. Is fluid but not excessive Does not appear to be crazed.
Is
very similar in color to the original PCA186. Upright test and flat tile are
very similar.
----------------------------------------------------------------------------
----
RRRPR194
a.. Feldspar G200 49.5
b.. Frit 3134 15.
c.. Whiting 10
d.. EPK 10
e.. Silica 15.5
Add:
a.. copper carb .35
b.. Tin ox l.0
Results: Smooth, Not runny, no visible crazing, color red/brown, upright
test
similar to flat tile.
----------------------------------------------------------------------------
----
RRRPR194
Add:
a.. copper carb .35
b.. tin Ox 2.0
Results: Smooth , Not runny, no visible crazing, color red/brown, upright
and
flat test similar
----------------------------------------------------------------------------
----
RRRPR194
Add:
a.. copper carb .35
b.. tin ox 3.0
Results: Smooth, bright, clear , no visible crazing, color bright red with
good
depth. dark flecks , both flat and upright tests similar.
appears to be fairly stable.
----------------------------------------------------------------------------
----
Findings: RRRPR194 is less fluid than RRRPR193. with 3.0 tin ox it is
very
close to the original Pete's Cranberry minus the running and crazing. It
would
be a very good substitute and deserves further testing.
The versions with 1.0 and 2.0 tin oxide are not as attractive even though
they
are stable. The color is definitely not bright clear read but brown red
running
close to that dreaded liver color.
RRRPR193 is more fluid, however, an improvement on the original Pete's
Cranberry. The colors might be a bit brighter in the lower tin ox range,
however,the 3.0 tin oxide is clearly superior in color compared to the 1.0
and
2.0.
I carefully examined all samples for crazing (in good lighting and with a
magnifying glass) however, I can't be positively certain there is no
crazing.
It appears there is none, However, on as small test piece which is
saturated
with color, it is surprisingly difficult to detect crazing.
On the samples that came out brown/red and dead looking...one could say that
part of the kiln received more reduction (i.e.carbon) which in turn muddied
the
samples. It is certainly a possibility. The kiln load consisted of 50%
Copper
Reds, all of the pots came out in their full red splendor in every part of
the
kiln. I also separated the flat test tiles from the upright tiles having
them
located in different parts of the kiln.
In conclusion:
Both tests RRRPR193 & RRRPR194 with 3.0 tin oxide are very good substitutes
for
the original Pete's Cranberry. I intend to further test these two in larger
quantities and on actual pots. Thanks Ron for your help.
Ingeborg Foco
Ron Roy on wed 29 dec 99
Hi again Ingaborg,
About the breaking on the rim - reducing the alumina in 194 will eventually
result in the breaking. Alumina is at the top of the list for viscosity of
the molten glaze and second highest for surface tension.
Just leave out the EPK and use OM#4 at 12, 10, and 8 - the lower the OM#4
the higher the expanasion gets so keep an eye out for crazing. There might
be a point where you get the break and not too much running. It will still
be a fairly well balanced glaze although the KNaO is high and could be a
problem with some acid foods - it would be interesting to have it tested
when you get down to the one you like - just ask to have it tested for
copper release. I am sure it will not be a problem because there is so
little copper to start with but testing is the only way to tell for sure.
RR
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
Ingeborg Foco on thu 30 dec 99
Hi Ron,
I'm sorry it has taken me so long to perform the "boiling freezing test" on
the samples. Unfortunately, it only took one turn into the boiling pot and
one plunge into ice water for all of the samples to craze. In good light
(we've been having spectacular sunny days) it was pretty easy to see the
crazing. Since I had 4 different clay bodies, there was a difference in the
craze pattern, i.e. some were quite large and others smaller and tighter.
So, back to the Laboratory for more testing. Will perform the tests per
your specs.
Ingeborg
----- Original Message -----
From: Ron Roy
To:
Sent: Wednesday, December 29, 1999 9:46 AM
Subject: Re: RR's Revision to Pete's Red
> ----------------------------Original message----------------------------
> Hi again Ingaborg,
>
> About the breaking on the rim - reducing the alumina in 194 will
eventually
> result in the breaking. Alumina is at the top of the list for viscosity of
> the molten glaze and second highest for surface tension.
>
> Just leave out the EPK and use OM#4 at 12, 10, and 8 - the lower the OM#4
> the higher the expanasion gets so keep an eye out for crazing. There might
> be a point where you get the break and not too much running. It will still
> be a fairly well balanced glaze although the KNaO is high and could be a
> problem with some acid foods - it would be interesting to have it tested
> when you get down to the one you like - just ask to have it tested for
> copper release. I am sure it will not be a problem because there is so
> little copper to start with but testing is the only way to tell for sure.
>
> RR
>
> Ron Roy
> 93 Pegasus Trail
> Scarborough
> Ontario, Canada
> M1G 3N8
> Evenings 416-439-2621
> Fax 416-438-7849
>
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