Robert A. Fox on sat 30 apr 11
Hi, I have a cone 10 glaze that I use with 5% rutile, but it often develo=
=3D
ps
pinholes near the top of the piece.=3D20
Would changing the rutile to titanium help any with the pinholes? Any oth=
=3D
er
ideas on how to get rid of them?=3D20
The glaze I use is a little bit runny and I tend to only get the pinholes=
=3D
at
the very tops of pieces. Also, I have noticed that if I have a decorative=
=3D
piece and don't glaze the inside, I do not get the pinholes.
Thanks
KATHI LESUEUR on sat 30 apr 11
On Apr 30, 2011, at 12:54 PM, Robert A. Fox wrote:
> Hi, I have a cone 10 glaze that I use with 5% rutile, but it often =3D
develops
> pinholes near the top of the piece.=3D20
>=3D20
> Would changing the rutile to titanium help any with the pinholes? Any =3D
other
> ideas on how to get rid of them?=3D20
>=3D20
> The glaze I use is a little bit runny and I tend to only get the =3D
pinholes at
> the very tops of pieces. Also, I have noticed that if I have a =3D
decorative
> piece and don't glaze the inside, I do not get the pinholes.
>=3D20
> Thanks
>=3D20
Robert,
This topic has come up a number of times on the list. I have a glaze =3D
that uses titanium and if I'm not careful I get pitting. The only thing =3D
I've come up with to stop it is to wash the pots before glazing to =3D
remove any possibility of dust. After glazing run you hand over the =3D
glaze surface even if you don't see any bubbles. Works for me.
KATHI LESUEUR
http://www.lesueurclaywork.com
David Hendley on mon 2 may 11
I have found that rutile or titanium, at concentrations over 5% can make
a glaze prone to pinholing. It makes no difference which is used.
Of course the usual advice for avoiding pinholes can be tried, such as
rinsing ware before glazing or soaking at top temperature so the pinholes
can smooth out.
I suggest you try reducing the percentage of rutile in the glaze. Perhaps
it will work and look similar with 3 1/2 or 4% rutile rather than 5%.
David Hendley
david@farmpots.com
http://www.farmpots.com
http://www.thewahooligans.com
----- Original Message -----
Hi, I have a cone 10 glaze that I use with 5% rutile, but it often develops
pinholes near the top of the piece.
Would changing the rutile to titanium help any with the pinholes? Any other
ideas on how to get rid of them?
Greg Marshall on wed 4 may 11
I use a Rutile blue glaze that contains 6% Rutile. Many years ago I was=3D=
20=3D
having problems with pinholes in the glaze. Jim McKinnell suggested I ad=
=3D
d 10%=3D20
gerstley borate to the glaze and I rarely have had pinholes since.
Robert Santerre on sat 7 may 11
Hi Robert,
I use a 7.5% rutile glaze as an overglaze layered on top of various base
glazes (a Tenmoku, a Celadon, etc.), firing to cone 10. Several years ago =
I
was also having serious pinholing problems. Tom Buck (in an unrelated
Clayart e-mail) mentioned that whiting can cause pinholing because CO2 is
evolved late in a cone 10 firing and suggested wollastonite could be
substituted for the whiting. I enlisted Ron Roy's help to reformulate my
glazes with wollastonite. Turned out that removing whiting from the rutile
glaze did NOT help, but removing whiting from all the base glazes had a
wonderful result ... no more pinholes! Conclusion: The whiting in my base
glazes was evolving CO2 that was bubbling up through the rutile overglaze
and causing the rutile pinholing. The titanium in rutile is quite
refractory and apparently quite viscous at cone 10 so the CO2 bubbles don't
heal over well at cone 10.
If you re-fire a piece, you'll note that the pinholes go away (are repaired=
)
and new ones do not appear ... all the CO2 (assuming you have whiting in
your glazes) is evolved in the first firing and the second firing acts
essentially like firing to a cone higher (cone 11) so the rutile melts more
and the pinholes are repaired.
Prior to stumbling (credit to Tom Buck and Ron Roy) onto this fix, I tried
firing to a higher bisque temp (from 06 to 04), carefully washing my bisque=
d
pots and soaking at cone 10 ... none of those procedures helped a bit
(actually the cone 10 soaking did help the pinholing, but my clay body was
getting over-fired and that caused blistering ... so I was just swapping on=
e
problem for another). I have not tried Greg Marshall's suggestion to add
Gerstley borate. My guess is that this addition lowers the melt temp of th=
e
rutile so it might work to heal over your pinholes. I should give it a try
... GB is a lot cheaper than Wollastonite ... and wollastonite (Vanisil W20=
)
is a bit difficult to work with. It does not mix well and you have to
essentially brush or hand rub the large particles through an 80 mesh screen
to get a good glaze mix (it may be that I'm too impatient here ... letting
the glaze mix set overnite might help this mixing problem ... gotta try
that).
Good luck, Bob
Bob & Ginny Santerre
Arrowsic Island Pottery
344 Old Stage Road
Arrowsic, ME 04530
(207) 443-5858
aipots@gwi.net
http://www.arrowsicislandpottery.com
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/
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-----Original Message-----
From: Clayart [mailto:Clayart@LSV.CERAMICS.ORG] On Behalf Of Robert A. Fox
Sent: Saturday, April 30, 2011 12:54 PM
To: Clayart@LSV.CERAMICS.ORG
Subject: Rutile and pinholes question
Hi, I have a cone 10 glaze that I use with 5% rutile, but it often develops
pinholes near the top of the piece.
Would changing the rutile to titanium help any with the pinholes? Any other
ideas on how to get rid of them?
The glaze I use is a little bit runny and I tend to only get the pinholes a=
t
the very tops of pieces. Also, I have noticed that if I have a decorative
piece and don't glaze the inside, I do not get the pinholes.
Thanks
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