Kelly Young on thu 12 feb 98
I fired my kiln last night and some of the pots had pinholes. Not all the pots.
Pots in top, bottom and middle of the kiln so that was not the problem. All
the pots were bisqued at the same time so that is not the problem. Mainly it
was one glaze, possibly two, I can't be sure because of layering. One peculiar
problem: One pot was a lided pot, single glaze inside and out. The inside of
the pot was beautiful, not one pinhole. The outside had a lot of pinholes.
Any ideas? Can pinholes form from cooling a pot too fast? The reason I ask is
every time I looked at the pots they seemed to have more pinholes than the time
before. I probably did unload my kiln too soon (cone 7 electric fire, opened
15 hours after it shut off, I know , I know) as I could hear dunting noises.
But I just couldn't wait......
TIA,
Kelly
Stephen Mills on fri 13 feb 98
Kelly
This sounds like slight underfire (glazes not quite finished gassing),
the comment about the inside of a pot being ok but not the outside gives
the clue (kiln within a kiln therefore hotter). Are you firing cones or
controller? If cones: slow down the firing a tad. If controller: check
it with cones, could be reading fast.
Steve
Bath
UK
In message , Kelly Young writes
>----------------------------Original message----------------------------
>I fired my kiln last night and some of the pots had pinholes. Not all the pots
> Pots in top, bottom and middle of the kiln so that was not the problem. All
>the pots were bisqued at the same time so that is not the problem. Mainly it
>was one glaze, possibly two, I can't be sure because of layering. One peculiar
>problem: One pot was a lided pot, single glaze inside and out. The inside of
>the pot was beautiful, not one pinhole. The outside had a lot of pinholes.
>Any ideas? Can pinholes form from cooling a pot too fast? The reason I ask is
>every time I looked at the pots they seemed to have more pinholes than the time
>before. I probably did unload my kiln too soon (cone 7 electric fire, opened
>15 hours after it shut off, I know , I know) as I could hear dunting noises.
>But I just couldn't wait......
>
>TIA,
>Kelly
>
--
Steve Mills
Bath
UK
home e-mail: stevemills@mudslinger.demon.co.uk
work e-mail: stevemills@bathpotters.demon.co.uk
BPS website: http://www.bathpotters.demon.co.uk
Ray Carlton on sat 14 feb 98
hi kelly,,,in answer to your Q> cooling too fast does not cause
pinholing... what may be causing it however is underfiring...pinholing is
caused by volatile gasses escaping throught the glaze in its molten
state...generally if you give it a bit longer at top temp, say another
30-40 minutes the craters that form when these volatiles escape will heal
over leaving no trace, you may find your glazes look a little better and
the problem will hopefully disappear...another approach is to adjust you
glaze a bit so that it matures at a slightlky lower temperature...do you
know these glazes well?? I have the impression that you may be fairly new
to all this....I would suggest perhaps if this is the case some great
references are available in particular "Clay and glazes for the potter" and
"porcelaine and stoneware" both by Daniel Rhodes are absolute treasure
troves of information about all aspects of our craft and even after 22
years i still find myself referring to these volumes...
good luck with it kelly
cheers :) Ray Carlton
McMahons Creek Victoria Australia
Mert & Holly Kilpatrick on tue 28 dec 99
------------------
The following glaze was posted a few years ago by Diane Woloshyn, and it is =
a
really nice offwhite matt (=5E6 electric). The one thing I would like to =
change
about it, where it gets thick, such as pooling in the bottom of something, =
it
tends to pinhole a little. Would it help to add a little frit? Can someone
give me a tip about a useful line of experimentation to try? I don't really
want to change the mattness, that's the trouble.
Nepheline syenite 35
Dolomite 14
Whiting 8
Zinc oxide 7
EPK 20
Flint 16
100
Analysis:
Na2O 0.14
K2O 0.05
MgO 0.19
CaO 0.40
ZnO 0.22
Al2O3 0.41
SiO2 1.97
Al:Si=3D1.00:4.79
A:N:A=3D1.00:0.41:1.97
Expansion: 76.5
Holly
Mark & Pauline Donaldson-Drzazga on wed 29 dec 99
----- Original Message -----
From: Mert & Holly Kilpatrick
To:
Sent: 28 December 1999 20:46
Subject: Pinhole question
----------------------------Original message----------------------------
------------------
The following glaze was posted a few years ago by Diane Woloshyn, and it is
a
really nice offwhite matt (^6 electric). The one thing I would like to
change
about it, where it gets thick, such as pooling in the bottom of something,
it
tends to pinhole a little. Would it help to add a little frit? Can someone
give me a tip about a useful line of experimentation to try? I don't really
want to change the mattness, that's the trouble.
Nepheline syenite 35
Dolomite 14
Whiting 8
Zinc oxide 7
EPK 20
Flint 16
100
Analysis:
Na2O 0.14
K2O 0.05
MgO 0.19
CaO 0.40
ZnO 0.22
Al2O3 0.41
SiO2 1.97
Al:Si=1.00:4.79
A:N:A=1.00:0.41:1.97
Expansion: 76.5
Holly
Dear Holly & Fellow Clayarters,
I had just made up a transposed (from 1215c to 1185c) glaze and tested well
but I thought I needed the blue to be a little more purple so I changed the
Potash Feldspar for Neph Syn. Guess what happened?, the glaze appearance
only changed by pinholing somewhat.
My answer would be to just replace the Neph Syn with Feldspar as a starting
point, and do any other balancing (if required) after testing this straight
swap. My amounts were also 35% of Neph Syn for Feldspar. Give it a shot as I
think it will answer your problem as it caused mine.
Happy potting Marek http://www.moley.uk.com
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