Corinne Null on wed 9 oct 96
I know we have covered pinholing exhaustively, but I am still having a
problem with 2 glazes. Is there a way to adjust the recipes to help?
I have 2 glazes that are pinholing each on their own, and together. It seems
to happen mostly in the electric kiln, but occassionally in the gas
reduction firings. Have tried smoothing with a finger before firing,
soaking at peak, and going slow midway through the firing. Any other
suggestions? Here are the cone 9 glazes, they're on Amherst Z clay. Would
going to cone 10 cause it? HELLLLLLPPPPPPP :0 !
TH Blue
potash feldspar 42.8
flint 26.6
whiting 22.1
epk 8.5
cobalt carb 1
blk nickel ox 1
titanium diox 3
Dark Shiny Blue
Kona F4 44.2
flint 23.6
whiting 15.4
ball clay 3.7
cornwall stone 22.7
cobalt carb 2.75
copper carb 4.38
TIA.
Corinne Null
Bedford, NH
cnull@mv.mv.com
Jeff Lawrence on wed 9 oct 96
>----------------------------Original message----------------------------
>I know we have covered pinholing exhaustively, but I am still having a
>problem with 2 glazes. Is there a way to adjust the recipes to help?
>
I read in Magic of Fire that whiting can be a pinholing offender. if you get
your CaO from wollastonite instead and reduce your flint, you shouldn't
affect your fired formula much, and may alleviate the pinholing. I dinked
around in Insight on your TH Blue to find that 26 wollastonite and 14 Flint
(versus 22.1 whiting and 26.6 Flint) get you essentially the same formula.
Good luck!
I hate those peksy little craters, too.
Jeff
Jeff Lawrence
jml@sundagger.com
Sun Dagger Design, Route 1 Box 394L, Espanola NM 87532
vox/fax: 505-753-5913
"Humor is the oil of civilisation."
Nils Lou on wed 9 oct 96
Sometimes pinholing is exacerbated by packing too tightly. Give your pots
room to breathe, at least one inch between surfaces. Nils Lou
On Wed, 9 Oct 1996, Corinne Null wrote:
> ----------------------------Original message----------------------------
> I know we have covered pinholing exhaustively, but I am still having a
> problem with 2 glazes. Is there a way to adjust the recipes to help?
>
> I have 2 glazes that are pinholing each on their own, and together. It seems
> to happen mostly in the electric kiln, but occassionally in the gas
> reduction firings. Have tried smoothing with a finger before firing,
> soaking at peak, and going slow midway through the firing. Any other
> suggestions? Here are the cone 9 glazes, they're on Amherst Z clay. Would
> going to cone 10 cause it? HELLLLLLPPPPPPP :0 !
>
> TH Blue
>
> potash feldspar 42.8
> flint 26.6
> whiting 22.1
> epk 8.5
> cobalt carb 1
> blk nickel ox 1
> titanium diox 3
>
>
> Dark Shiny Blue
>
> Kona F4 44.2
> flint 23.6
> whiting 15.4
> ball clay 3.7
> cornwall stone 22.7
> cobalt carb 2.75
> copper carb 4.38
>
> TIA.
>
> Corinne Null
> Bedford, NH
>
> cnull@mv.mv.com
>
Sue Davis on wed 9 oct 96
Hi, I work in Majolica but had pinholing problems galore! The solution was to
run the glaze through a 120 mesh seive. For this I had to buy a Talisman
seive but the extra cost was worth it. The potter who passed on this
information said it also corrected pinholing at higher temps: ie cone 6
through ^10. Hope this helps you.
Sue
Sunny Florida is finally getting some cooler weather.
Patsy Catsos on thu 10 oct 96
Bisque firing to a higher temp helped me once. Dampening pots before
applying glaze might help. Patsy
David Hewitt on sat 12 oct 96
In message , Corinne Null writes
>----------------------------Original message----------------------------
>I know we have covered pinholing exhaustively, but I am still having a
>problem with 2 glazes. Is there a way to adjust the recipes to help?
>
Before altering the recipe, which may alter the glaze in some respect,
have you considered the following:-
1) Increasing the biscuit firing temperature in order to burn out more
of the volatile material which may be giving rise to gas bubbles that
are causing the pinholing.
2) Soaking for longer at the maximum firing temperature, say 30 minutes
longer, whatever you are now doing.
3) Cool the glaze more slowly for the first 100 C down from top
temperature.
4) A thinner glaze application in general gives less pinholing but too
thin can change the glaze appearance / colour and may not be an option.
Avoid it being too thick.
If none of these help, please come back again.
David Hewitt
David Hewitt Pottery Caerleon, Tel:- 01633 420647
7 Fairfield Road, Caerleon, Newport, South Wales, UK.
URL http://digitalfire.com/magic/hewitt.htm
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