Mary O'Connell on thu 30 jan 03
Dear Clayarters,
I am experiencing pinholing in the below listed recipe for Titanium =
White, can anyone run it through a glaze calc. program and let me know =
what is up? It leaves pinholing on many of the claybodies we use at the =
Art and Craft Center I teach at (porcelain - stoneware). I am thinking =
of substituting Wollastonite for the Whiting (per Ron/John's book) but =
don't quite know where to go with it.
TITANIUM WHITE (cone 6, oxidation)
Custer Feldspar 41.3
Whiting 16.9
Zinc Oxide 12.0
Kaolin (EPK) 4.0
Flint 26.9
Titanium 5.0
Thanks to those who respond.
Regards,
Mary O'Connell
moconnell@inil.com
Ron Roy on fri 31 jan 03
Hi Mary,
There can be a number of reasons for pinholes - I'll provide a short list
and we can go from there.
1. Stiff glazes - like those high in alumina - cannot easily flow enough to
seal over the natural bubbles that form when glazes melt - taking out
alumina or holding temperature longer to give them time to seal over would
be my usual recommendation. This is not the cause in your glaze - the
alumina is quite low for a cone 6 glaze - and probably not very stable in
use because of that.
2. If bisque firing is too fast and/or not enough oxygen is present to burn
out impurities during the bisque firing - certain bodies - especially those
with iron - will over fire - producing gases which result in blistering
and/or pinholing. This could be your problem - if the pinholes get worse on
refiring.
3. Some bodies are not well formulated and are overfired - even at the
temperature they are said to work at. Many clay manufactures do not test
there clays and the natural variation of the raw materials we make our
clays out of can conspire to over fire. This could also be your problem -
same as #2.
4. Glazes high in Zinc oxide (like this one) are well know to promote pin
holing - because - zinc oxide is very easily reduced, it turns to the metal
zinc which melts at 419C and boils at 925C. The result is bubbles of
vaporized zinc in the glaze - in fact being lost to the glaze - and it's a
flux - loss of flux means stiffer glaze - stiffer glaze means bubbles have
a harder time healing over. Read the Hamer section on Zinc - it's all
there.
So how can it get reduced - if bisque firings are not "clean" some organics
are still in the clay - that can reduce the ZnO - if bisque firings are
done quickly - the products of combustion can permeate the brick and can be
there for subsequent glaze firings. Then there is the wax burning off
during the glaze firing. A kiln vent goes a long way to avoid this because
of the constant supply of oxygen being drawn into the kiln during both
bisquing and glaze firing.
5. Some potters have experienced problems with new supplies of rutile -
which is a frequent source of TiO2.
What to look for - is the pin holing happening more with the stoneware clay
as opposed to the porcelains? Is there still smoke coming out of the bisque
kilns at shut off - is there any smoke around during the glaze firings. Did
the problem start happening when you got a new batch of TiO2 or rutile? Has
anyone altered the firing schedules. Are the ducts from your vent leaking
so they are not working properly?
Subbing wolastonite will not fix the problem if I am correct by the way -
so by all means try it. Here is the altered recipe. By the way - the
original recipe totals 106.1 - hope I am working with a full deck
here????????? It is alway a good idea to include the total when posting
recipes - even if you are just keeping track of your own - just in case you
ever to have questions about the accuracy - it is so easy to make errors
when copying.
Titanium white (cone 6) rr revised
Custer - 40.5
Wolastonite - 23.5
ZnO - 13.0
EPK - 4.5
Silica - 18.5
TiO2 - 5.0
Total 105.0
Let us know the results please Mary - RR
>I am experiencing pinholing in the below listed recipe for Titanium White,
>can anyone run it through a glaze calc. program and let me know what is
>up? It leaves pinholing on many of the claybodies we use at the Art and
>Craft Center I teach at (porcelain - stoneware). I am thinking of
>substituting Wollastonite for the Whiting (per Ron/John's book) but don't
>quite know where to go with it.
>
>TITANIUM WHITE (cone 6, oxidation)
>
>Custer Feldspar 41.3
>Whiting 16.9
>Zinc Oxide 12.0
>Kaolin (EPK) 4.0
>Flint 26.9
>Titanium 5.0
>
>Thanks to those who respond.
>
>Regards,
>
>Mary O'Connell
>moconnell@inil.com
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
David Hewitt on fri 31 jan 03
In answer to your question of substituting Wollastonite for Whiting, the
reformulated recipe would read as follows:-
Custer feldspar 41.94
Wollastonite 19.87
Zinc oxide 12.16
EPK 4.02
Flint 16.94
Titanium dioxide 5.07
_____
100.00
I notice that your recipe adds up to 106.1. I have taken your figures
and assume that they are correct.
Have you tried firing to just a little higher temperature?
David
In message , Mary O'Connell writes
>Dear Clayarters,
>
>I am experiencing pinholing in the below listed recipe for Titanium White, can
>anyone run it through a glaze calc. program and let me know what is up? It
>leaves pinholing on many of the claybodies we use at the Art and Craft Center I
>teach at (porcelain - stoneware). I am thinking of substituting Wollastonite for
>the Whiting (per Ron/John's book) but don't quite know where to go with it.
>
>TITANIUM WHITE (cone 6, oxidation)
>
>Custer Feldspar 41.3
>Whiting 16.9
>Zinc Oxide 12.0
>Kaolin (EPK) 4.0
>Flint 26.9
>Titanium 5.0
>
>Thanks to those who respond.
>
>Regards,
>
>Mary O'Connell
>moconnell@inil.com
--
David Hewitt
David Hewitt Pottery
7 Fairfield Road, Caerleon, Newport,
South Wales, NP18 3DQ.
Tel:- +44 (0) 1633 420647
Fax:- +44 (0) 870 1617274
Web:- http://www.dhpot.demon.co.uk
Ababi on fri 31 jan 03
Hello Marry
When a recipe has numbers like
>Custer Feldspar 41.3
>Whiting 16.9
>Kaolin (EPK) 4.0
>Flint 26.9
I expect it will finish in 100
Here is yours:
TITANIUM WHITE
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
Cone 6 1222 deg.C. -
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
Custer feldspar 41.00
Calcium Carbonate 16.90
zinc oxide 12.00
EPK Kaolin 4.00
Titanium Dioxide 5.00
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
Seger Weight%
KNO 0.169 7.50%
CaO 0.443 13.12%
MgO 0.000 0.01%
ZnO 0.388 16.68%
Al2O3 0.221 11.88%
P2O5 0.000 0.01%
SiO2 1.325 42.07%
TiO2 0.207 8.72%
K2O 0.116 5.78%
Na2O 0.053 1.73%
Al:Si 6.00
Expan. 9.54
ST 388.05
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
I will note deal with the expansion because or pinholes because I do not have enough
of these problem to be able to learn how to overcome them.
The Zinc is very high,- but I love zinc. You can add 1-2 nickel to get yellow green or
remove the titanium and add nickel and get blue.
The silica and alumina are too low.
I try to see what to do in the two ways, your glaze as it is and the glaze if there was
100 means: 21.1 flint
As it is
TITANIUM WHITE1
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
Cone 6 1222 deg.C. -
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
Custer feldspar 42.00
Wollastonite 23.40
zinc oxide 12.80
EPK Kaolin 16.40
Titanium Dioxide 5.40
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
Seger Weight%
KNO 0.161 5.67%
CaO 0.434 10.18%
MgO 0.022 0.37%
ZnO 0.383 13.02%
Al2O3 0.330 14.07%
P2O5 0.001 0.04%
SiO2 1.978 49.70%
TiO2 0.208 6.94%
K2O 0.111 4.37%
Na2O 0.050 1.30%
Al:Si 5.99
Expan. 8.29
ST 389.65
If there was more flint:
Still it has too low alumina silica I will add them slightly to keep it's character.
and change as you have offered the whiting into Wollastonite.
TITANIUM WHITE WITH FLINT1
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
Cone 6 1222 deg.C. -
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
Custer feldspar 20.40
Wollastonite 21.40
zinc oxide 11.70
EPK Kaolin 13.20
Titanium Dioxide 5.50
Flint 14.90
frit 3110 13.00
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
Seger Weight%
KNO 0.171 5.09%
CaO 0.446 10.02%
MgO 0.021 0.34%
ZnO 0.362 11.82%
Al2O3 0.232 9.46%
P2O5 0.001 0.03%
B2O3 0.012 0.34%
SiO2 2.320 55.89%
TiO2 0.219 7.01%
K2O 0.064 2.43%
Na2O 0.107 2.66%
Al:Si 10.02
Expan. 8.08
ST 373.39
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
Suggestions:
Read my article
http://members4.clubphoto.com/ababi306910/912566/
Try to apply on the last recipe a higher alumina blue glaze or any higher alumina glaze
with some colorants like opal blue floating blue, whatever!
Ababi Sharon
Glaze addict
Kibbutz Shoval Israel
ababisha@shoval.org.il
http://members4.clubphoto.com/ababi306910/
http://www.milkywayceramics.com/cgallery/asharon.htm
and also
http://www.israel-ceramics.org/membersGallery/personalpage.asp?MID=507
---------- Original Message ----------
>Dear Clayarters,
>I am experiencing pinholing in the below listed recipe for Titanium White, can anyone
run it
>through a glaze calc. program and let me know what is up? It leaves pinholing on
many of
>the claybodies we use at the Art and Craft Center I teach at (porcelain - stoneware).
I am
>thinking of substituting Wollastonite for the Whiting (per Ron/John's book) but don't
quite
>know where to go with it.
>TITANIUM WHITE (cone 6, oxidation)
>Custer Feldspar 41.3
>Whiting 16.9
>Zinc Oxide 12.0
>Kaolin (EPK) 4.0
>Flint 26.9
>Titanium 5.0
>Thanks to those who respond.
>Regards,
>Mary O'Connell
>moconnell@inil.com
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
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>settings from http://www.ceramics.org/clayart/
>Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
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