search  current discussion  categories  glazes - faults 

pinholing

updated tue 29 may 12

 

Diana Mannino on fri 5 dec 97

After a ten year clay lapse, I ve been working for three years as a
basicallly self-taught studio potter in Cortona, Italy.
I have come up against one consistent problem that I can t find the
solution for...who can possibly help me??? The problem is pinholing. I
use a buff low temp. clay which melts at 04. I apply a white slip,
(comes in dried chunks for slip casting use...max firing temp. is 03),
over leather hard pieces. I often first colour the slip with prepared
Colorobbia stains. Then I bisque to 06 in my gas kiln. I then use the
pure stains for stronger decoration, glaze with a shiny transparent
cristallina and re-fire to the maturing temp. of the glaze 09/08. I
soak for half an hour. After speaking with the owner of the clay
processing plant I began taking the bisque up to 05 and soaking for an
hour for a total of a 6 1/2 hr. firing. The glaze definately comes out
smoother and thick like butter, but I still have the pinholing. I even
began air-blowing each piece before glazing to insure dust removal. If I
don t pass a finger over the entire surface after glazing the pinholing
is worse. I m desperate!!! I ve read that dampening the piece before
immersing it into the glaze should help, but as I use underglaze
decoration I can t see how I can moisten without smudging. Any ideas
are greatly appreciated! Grazie!
Diana Mannino
Cortona, Italia

Marshia Hall on thu 3 sep 98

Hi folks;

To my deep sorrow, I've had a continuing pinholing problem with my new Olsen
16 cu ft. kiln since it was built in May. 12 firings later, and 10 different
strategies later, I found a bit of relief last firing by opening up the air
ports on the burners all the way. I fire to cone 10 reduction (slight) with a
white stoneware clay.

I have:

lowered bisque temp* fired with lid cracked in bisque to 1200F* used
different clay * used different glaze* slowed the firing * increased the soak
time at end * cleaned the bisque ware * prayed * called potter friends *
called Fred Olsen...still, pinholes persist.

Anybody got any other ideas to try besides a virgin in the volcano boogie?

Thanks ever so much for your educated response.

marshia in Tuolumne

Kris Bliss on fri 4 sep 98

>----------------------------Original message----------------------------
>Hi folks;
>
> To my deep sorrow, I've had a continuing pinholing problem with my
new Olsen
>16 cu ft. kiln since it was built in May. >
> Anybody got any other ideas to try besides a virgin in the volcano
boogie?
>
> marshia in Tuolumne
>

Dear marshia,
I too have a 16 ft. olsen, alth it's very old...
The pinhole problem seems to occur in the top 1/3 of the kiln.
My solution has been to :
a. fire longer
b. soak for aprox 20 min at the end
c. do not "clear" the kiln at the end, just close while
still in reduction.
hope this helps, and good luck.
ttfn, kris


kbliss@customcpu.com
Anchorage, Alaska

gwalker on fri 4 sep 98

Marshia,

Why did you LOWER the bisque temperature? Surely it would be wiser to
RAISE it? We have a local clay that MUST be bisqued at 1000 C or higher
or it will cause pinholing in the glaze firing.

Good luck!

Geoff.

Kathi LeSueur on sat 5 sep 98

I was plagued with pinholing in a very reliable glaze after I rebuilt my kiln.
The most significant fact in the end was that I was now firing in 11 or 12
hours instead of the usual 18. I've made a number of changes in both the way I
apply glazes and the way I fire.

Glazing:
1. Brush off the ware with a soft brush to remove dust.
2. Wipe the pieces down with a damp sponge just before dipping.
3. After the glaze has dried and before applying any brush decoration, I run
my fingers lightly over the whole surface to get rid of any possible surface
bubbles.

Firing:
1. I've stopped firing the same day that I glaze. I always wait overnight to
turn on the kiln. This is hard since I'm ALWAYS up against a deadline.

2. I make sure the kiln is in total oxidation until cone 010 bends. I think
this is the one single most important factor. It's necessary to completely
burn out the carbon in the early stages of firing. When cone 010 bends I cut
the blowers and gas back drastically to slow it down. I also do a slight body
reduction at this point.

3. When cone 05 bends I put the kiln back into oxidation and leave it that way
until cone 8 begins to bend. At that point I slow the burners even further and
put it into a medium reduction until cone 10 drops.

4. Once cone 10 drops I cut the burners back so that they are barely on
(making sure to maintain reduction) and soak for 40 minutes.

Cone 010 usually drops at about the fifth hour of firing. It's another 8 hours
to completion. From the time cone 8 starts to tip until cone 10 is down can be
as long as 3 hours. This is extreme, but I find it works for me.

I use a Bacarach co2 analyzer to measure reduction. I body reduce at 9% co2
and glaze reduce at 9 1/2 %. From cone 05 until cone 8, the analyzer usually
reads 11% co2. The higher the number the less reduction (closer to a neutral
flame).

Hope this is of some help.

Kathi LeSueur

Jandira Shelley on sun 21 feb 99

fIRING CONDITIONS:
CLAY: STANDARD #112 WITH MANGANESE, CONE 6
GLAZES: OPPULENCE GLAZES BY MID-SOUTH CERAMICS
FIRED FOR 1.5 HOURS ON LOW, 1.5 HOURS ON MEDIUM, AND 6 HOURS ON HIGH (KILN
SITTER SHUT OFF AFTER 8 TOTAL HOURS, BUT SENIOR CONE 6 HAD NOT DROPPED, SO WE
FIRED FOR ABOUT 1 HR. LONGER ON HIGH UNTIL CONE 6 HAD DROPPED,AND THEN SOAKED
FOR 1 HR. ON MEDIUM. PINHOLING OCCURRED TO SOME DEGREE IN ALL PIECES. ANY
IDEAS WHY?


Jeanne Murdock on wed 24 feb 99

At 11:26 AM 2/21/99 -0500, you wrote:
>----------------------------Original message----------------------------
Hell-o

I am using standard's dark chocolate clay. I've had the same pinhole situation.
I now fire VERY SLOWLY. That's bisque and glaze and I fire to cone 5 instead
of cone 6.
Good luck
jeanne concord, nc>


fIRING CONDITIONS:
> CLAY: STANDARD #112 WITH MANGANESE, CONE 6
> GLAZES: OPPULENCE GLAZES BY MID-SOUTH CERAMICS
> FIRED FOR 1.5 HOURS ON LOW, 1.5 HOURS ON MEDIUM, AND 6 HOURS ON
HIGH (KILN
>SITTER SHUT OFF AFTER 8 TOTAL HOURS, BUT SENIOR CONE 6 HAD NOT DROPPED, SO WE
>FIRED FOR ABOUT 1 HR. LONGER ON HIGH UNTIL CONE 6 HAD DROPPED,AND THEN SOAKED
>FOR 1 HR. ON MEDIUM. PINHOLING OCCURRED TO SOME DEGREE IN ALL PIECES. ANY
>IDEAS WHY?
>
>

matthew lettington on thu 25 feb 99

------------------
iN my expierience manganese will always give blistering or pinholling. YOu
oculd try changing the actuall glaze base that you are using
-----Original Message-----
From: Jeanne Murdock =3CDiscvrncly=40CTC.Net=3E
To: CLAYART=40LSV.UKY.EDU =3CCLAYART=40LSV.UKY.EDU=3E
Date: 1999=B3=E2 2=BF=F9 24=C0=CF =BC=F6=BF=E4=C0=CF =BF=C0=C8=C4 10:58
Subject: Re: PINHOLING


----------------------------Original message----------------------------
At 11:26 AM 2/21/99 -0500, you wrote:
=3E----------------------------Original message----------------------------
Hell-o

I am using standard's dark chocolate clay. I've had the same pinhole
situation.
I now fire VERY SLOWLY. That's bisque and glaze and I fire to cone 5 instead
of cone 6.
Good luck
jeanne concord, nc=3E


fIRING CONDITIONS:
=3E CLAY: STANDARD =23112 WITH MANGANESE, CONE 6
=3E GLAZES: OPPULENCE GLAZES BY MID-SOUTH CERAMICS
=3E FIRED FOR 1.5 HOURS ON LOW, 1.5 HOURS ON MEDIUM, AND 6 HOURS ON
HIGH (KILN
=3ESITTER SHUT OFF AFTER 8 TOTAL HOURS, BUT SENIOR CONE 6 HAD NOT DROPPED, =
SO
WE
=3EFIRED FOR ABOUT 1 HR. LONGER ON HIGH UNTIL CONE 6 HAD DROPPED,AND THEN
SOAKED
=3EFOR 1 HR. ON MEDIUM. PINHOLING OCCURRED TO SOME DEGREE IN ALL PIECES.
ANY
=3EIDEAS WHY?
=3E
=3E

Ron Roy on sun 28 feb 99

Breathing clay dust with manganese in it - and breathing fumes from firing
such clay are two excellent ways to get manganese poisoning - bad news from
any point of view.

RR

>>----------------------------Original message----------------------------
>Hell-o
>
>I am using standard's dark chocolate clay. I've had the same pinhole
>situation.
>I now fire VERY SLOWLY. That's bisque and glaze and I fire to cone 5 instead
>of cone 6.
>Good luck
>jeanne concord, nc>
>
>
>fIRING CONDITIONS:
>> CLAY: STANDARD #112 WITH MANGANESE, CONE 6
>> GLAZES: OPPULENCE GLAZES BY MID-SOUTH CERAMICS
>> FIRED FOR 1.5 HOURS ON LOW, 1.5 HOURS ON MEDIUM, AND 6 HOURS ON
>HIGH (KILN
>>SITTER SHUT OFF AFTER 8 TOTAL HOURS, BUT SENIOR CONE 6 HAD NOT DROPPED, SO
>WE
>>FIRED FOR ABOUT 1 HR. LONGER ON HIGH UNTIL CONE 6 HAD DROPPED,AND THEN
>SOAKED
>>FOR 1 HR. ON MEDIUM. PINHOLING OCCURRED TO SOME DEGREE IN ALL PIECES.
>ANY
>>IDEAS WHY?
>>
>>

Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849

Web page: http://digitalfire.com/education/people/ronroy.htm

Cindy Strnad on fri 2 feb 01


Ken,

I think, from the sound of your post, that the pinholes are likely to be the
result of out-gassing of the clay. You obviously know enough to keep the
bisque free of dust, and you've fired this glaze successfully at ^5 for some
time now. I would have said maybe you should fire to ^6, which is the temp I
take the same glaze to, but if it's been working . . . .

Try holding your bisque kiln at 1870F or so for an hour. Use a shelf cone to
make sure you don't over-fire. The idea is to keep it hot long enough to
release the gasses, but not so long that you end up firing a cone or so
higher than you intended.

You might also consider a longer hold (done in the same way) for your glaze
firing. I wouldn't think, at the speed you're firing, that this would be
necessary, but if holding the bisque doesn't work, you might try it.

Cindy Strnad
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730
USA
earthenv@gwtc.net
http://www.earthenvesselssd.com

Ken Russell on fri 2 feb 01


I have a pinhole problem and can't figure out what I'm doing wrong. =20

My clay is Tucker MidCal5 w/ mang. I apply cobalt, black copper, =
manganese, or chrome/cobalt wash to pots for under glaze color just =
after throwing.

My bisque fire schedule is:
0-200 rate 100F/hr hold 3.5 hours (for candling)
200-1000F rate 175/hr hold 0.0
1000-1891 rate 150/hr hold 0.0

Glaze is Hansen Cone 5 Base w/4% Zircopax, 1% Tin Ox

Hansen Base:

20% Silica (325)
20% Custer (325)
20% Wollastonite
20% 3134
20% China Clay (sometimes I use EPK when I can't get the English China =
Clay)

Glaze fire schedule:

0-250 @100F/hr Hold 0
250-1000F @ 250/hr Hold 0
1000-1300F @ 150/hr Hold 0
1300-1685F @ 180/hr Hold 0
1685-2199 @ 80/hr Hold 10 minutes

I fire in 5 KM1227's all ITC 100 coated. =20

The pin holes are worse (read lots on pinholes per square inch) under =
cobalt oxide, not as bad under black copper and much less on the plain =
base glazed areas. The pin holes are all VERY, VERY tiny but =
noticeable. My old clay body was Continental MidRange w/ mang and I =
didn't have any pinholing problems at all using the same firing =
schedules and base glaze. However, other things required me to change =
clay bodies. The clay is superior to anything I've ever used in the =
past in every aspect except for this weird tiny pinholing.

Any help with firing schedules, base glaze suggestions would be =
appreciated.

Ken Russell
The Russell Pottery
gone2pot@ispchannel.com

Ceramic Design Group on sat 3 feb 01


on 2/2/01 9:04 AM, Ken Russell at gone2pot@ISPCHANNEL.COM wrote:

> I have a pinhole problem and can't figure out what I'm doing wrong. =20
>
> My clay is Tucker MidCal5 w/ mang. I apply cobalt, black copper, =
> manganese, or chrome/cobalt wash to pots for under glaze color just =
> after throwing.


I think that the pinholing is resulting from the reaction of the wash with
the clay underneath it as well as the glaze over it.
The materials in the wash are basically refractory, way refractory, and are
contributing to the overall problem. I am not familiar with the clay body,
but I am sure Frank Tucker could provide you with some basic information.
>
> My bisque fire schedule is:
> 0-200 rate 100F/hr hold 3.5 hours (for candling)
> 200-1000F rate 175/hr hold 0.0
> 1000-1891 rate 150/hr hold 0.0

I find nothing wrong with this bisque firing schedule other than it could
use maybe a soak at 1000F for about half an hour. Our bisque kilns ramp at a
much faster temperature after a few hours warm up to 250F.
>
> Glaze is Hansen Cone 5 Base w/4% Zircopax, 1% Tin Ox
>
> Hansen Base:
>
> 20% Silica (325)
> 20% Custer (325)
> 20% Wollastonite
> 20% 3134
> 20% China Clay (sometimes I use EPK when I can't get the English China =
> Clay)

We have used this formula and it does work fine. There is of course some
outgasing from the Wollastonite but coupled with your overly cautions glaze
firing schedule, I don't think that the problem is the glaze.
>
> Glaze fire schedule:
>
> 0-250 @100F/hr Hold 0
> 250-1000F @ 250/hr Hold 0
> 1000-1300F @ 150/hr Hold 0
> 1300-1685F @ 180/hr Hold 0
> 1685-2199 @ 80/hr Hold 10 minutes

Incorporate a longer soak slightly below where you want cone 5 to be over,
so you are slightly underfiring the end point of the cone but using a soak
at the end to mature the glaze and have it fire to the proper end point.
>
> I fire in 5 KM1227's all ITC 100 coated. =20

No big problem here
>
> The pin holes are worse (read lots on pinholes per square inch) under =
> cobalt oxide, not as bad under black copper and much less on the plain =
> base glazed areas.

Basically you have answered your questions with these kind of "test" areas.
Black copper oxide is very refractory and is not letting the glaze on top
fully mature. Whether the pin holes are tiny or large if not the issue. The
wash under the glaze, with lots of O2 outgassing from these materials
especially chrome with is VERY refractory is a large part of your problem.
How's about using these materials, or commercial stains OVER the glaze for
whatever decorative effects you wish.

> The pin holes are all VERY, VERY tiny but =

The fact that you are having pinholing no matter the size is indicative of a
much larger problem.

> noticeable. My old clay body was Continental MidRange w/ mang and I =
> didn't have any pinholing problems at all using the same firing =
> schedules and base glaze. However, other things required me to change =
> clay bodies. The clay is superior to anything I've ever used in the =
> past in every aspect except for this weird tiny pinholing.

As I mentioned, I am not really familiar with these clay bodies, but I would
also suspect that they may be contributing to the problem. Have you tried
any white ware bodies at that temperature?
>
> Any help with firing schedules, base glaze suggestions would be =
> appreciated.

Summary: firing schedules ok with the exception of a longer soak at the end.
Clay bodies? Unknown to me. Base glaze, should not be a problem. Under the
glaze raw oxide washes? Yes, therein IMHO, is the source of the problem.

Best

Jonathan

Jonathan Kaplan, president
Ceramic Design Group
PO Box 775112
Steamboat Springs CO 80477
voice and fax 970 879-9139
jdkaplan@cmn.net
info@ceramicdesigngroup.net

Plant Location:
1280 13th Street Unit 13
Steamboat Springs CO 80487
(please use this address for all deliveries via UPS, common carrier, Fed Ex,
etc.)

"Custom design and manufacturing for the ceramic arts, giftware and pottery
industries. Molds, models, and tooling for slip casting, jiggering and
hydraulic pressing. Consultation on technical issues such as clay bodies
glazes, and kilns."

Paul Taylor on sun 4 feb 01


Dear Ken

Pinholing is a real B

When it arrives it arrives with the bad fairy that clouds the mind and
fills it with a fog of confusion . The effect is that you can't even
remember what you did before and what has changed - the more you think about
it the more the possibilities there seem to be.

We know as I expect you know it is gas that causes it. Gas can come
either from the clay or the slip (Color wash) or the glaze.

We know its the clay because you have changed it.

What is different about the clay. Firstly it could contain more carbon
and or sulphates and god knows what other nasties that are burnt off in the
biscuit. Secondly And/or the distribution of the particle size of the bits
that make up the body could have changed .

If The clay contains more carbon it is straight forward to deal with you
increase the oxygen and or firing time when the gas is burnt off and make
sure you do it before your body closes its pores and the glaze and slip
starts to seal over.

The second is a theory of mine only born out by my field experience I
have been wrong before but here goes.

Some clays have very fine particles but are mixed with particles that
are large and others may be made up of all medium sized particles - I could
give some measurements but I think we are confused enough.

What happens when you change from a clay with lots of medium particles
to say a ball clay body that has fine and large particles added as a grog is
that the fine particles conspire to close up the pores of the body earlier
especially at the body glaze/slip interface layer to trap nasties like
carbon at a lower temperatures than the more medium particled body. (YOU
will have to read that more than once sorry)

The ball clay bodies are nicer to throw with they are very plastic and
good workable strength; but the more boring gray and dull buff stonewares
are open pored at biscuit and easy to get the carbon out, even though they
may contain more carbon to start with.

Another point to this theory is that small particle size acts as a
catalyst and melts and sinters at lower temperatures especially when
compounded by a slip layer that fluxes the inter body layer more, catches
the carbon ready to release it into the glaze at a higher temp when the
glaze is trying to settle . Of coarse some glazes have little enough surface
tension and allow the gas not to unduly affect them but glazes with a higher
surface tension or at the bottom of their firing range may show pinholes.

Also ball clay bodies contain fire clay grogs which could be any floor
sweepings giving off enough "ites and ides" to worry the worried and pinhole
the glaze .

Slip body layers are terrible for trapping carbon which is why they can
be so difficult to handle - cracking off leaving a black underneath. Since
it is effecting the glaze with out a slip area we can deduce that it is
probably not the slip.

so It is either the clay is throwing off some gas at vitrification or the
inter glaze or/and slip layer is slowing down the gas and not letting it
escape in time. The trouble is that holding the biscuit and or the glaze
firing temperature at 850 centigrade might not help, because I do not know
what the gas is leaving or when he gas is leaving the slip body layer

What are you going to do.

Go back to the old clay until the problem is fixed is the first step.

Then you try a new firing with tests either soak or better fire the kiln
more slowly for the whole process. Double or triple your firing time from
600c to 1000C all round, with plenty of oxygen, biscuit and glaze, if that
cures it you are laughing. All then you have to do is find out at what
temperature the gas is best liberated by making the window that you crawl
fire smaller from 700 to 1000 etc etc . Be careful because your kiln will
not fire evenly at these temperatures so don't cut it too fine. These tests
will not effect your old ware too much but watch for porosity differences
when glazing. If the first test firing is biscuited a cone lower than you
usually go all the better.

If that does not cure the problem you are going to have to change the
recipes either drastically which can make too much of a change to the look
of the ware or a series of small adjustments to everything trying to
maintain the look you want . The trouble with making small adjustments to
every thing is that it is difficult to arrange a series of experiments that
will not take generations. This is the time we start to realize that pottery
is sooner or later a compromise and that we have to make do with what we
have.

By the by, some glazes with Zircon in love to pinhole when only slightly
under fired . You could try another five degrees it makes all the difference
to my zircon glaze. Why such a small difference I do not know. I suspect
Zircon has a similar effect as adding too allumina - increases the viscosity
and narrows the firing range ???



If sulphur gas is your problem; Some one more experienced than I may
comment on that. I do not know what to do if you can do anything. It is
difficult because you are dealing with sulphates and sulfites and a bit of
reduction helps and glazes that do not tend to pinholing.

I think there is the solution to the problem but I could be very wrong
pin holing is like that, a B - that fairy again


Regards from Paul Taylor
http://www.anu.ie/westportpottery

There are two sides to an argument - ignorance and self interest.


> From: Ken Russell
> Reply-To: Ceramic Arts Discussion List
> Date: Fri, 2 Feb 2001 10:04:45 -0600
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Pinholing
>
> I have a pinhole problem and can't figure out what I'm doing wrong.
>
> My clay is Tucker MidCal5 w/ mang. I apply cobalt, black copper, manganese,
> or chrome/cobalt wash to pots for under glaze color just after throwing.
>
> My bisque fire schedule is:
> 0-200 rate 100F/hr hold 3.5 hours (for candling)
> 200-1000F rate 175/hr hold 0.0
> 1000-1891 rate 150/hr hold 0.0
>
> Glaze is Hansen Cone 5 Base w/4% Zircopax, 1% Tin Ox
>
> Hansen Base:
>
> 20% Silica (325)
> 20% Custer (325)
> 20% Wollastonite
> 20% 3134
> 20% China Clay (sometimes I use EPK when I can't get the English China Clay)
>
> Glaze fire schedule:
>
> 0-250 @100F/hr Hold 0
> 250-1000F @ 250/hr Hold 0
> 1000-1300F @ 150/hr Hold 0
> 1300-1685F @ 180/hr Hold 0
> 1685-2199 @ 80/hr Hold 10 minutes
>
> I fire in 5 KM1227's all ITC 100 coated.
>
> The pin holes are worse (read lots on pinholes per square inch) under cobalt
> oxide, not as bad under black copper and much less on the plain base glazed
> areas. The pin holes are all VERY, VERY tiny but noticeable. My old clay
> body was Continental MidRange w/ mang and I didn't have any pinholing problems
> at all using the same firing schedules and base glaze. However, other things
> required me to change clay bodies. The clay is superior to anything I've ever
> used in the past in every aspect except for this weird tiny pinholing.
>
> Any help with firing schedules, base glaze suggestions would be appreciated.
>
> Ken Russell
> The Russell Pottery
> gone2pot@ispchannel.com

Ken Russell on sun 4 feb 01


Re: Cindy

According to my cone chart in my Skutt manual, I'm firing to cone 6 (2199=^6
at 108F/hr for the last hour in their chart. I'm using 80F/hr. Hmmm). I
also tried a 30 minute soak at the end of the glaze fire with no noticeable
difference. I'm a little scared to hold a bisque fire at that temperature
(1870F) for too long, being as I might exceed the time and temp for cone05
and head into vitrification/stoneware country. I guess I figure the
ridiculously cautious bisque ramp rate would burn the carbon and other crap
out long before reaching ^05. It certainly did with the other clay body.

Thanks for your help.

Re Jonathan

Like I mentioned to Cindy, I soaked one load (glaze fire at 2199) for half
an hour with no noticeable differences. The raw oxides beneath the same
glaze never pinholed at all with the other clay bodies, so I'm a little
suspicious that suddenly the raw oxides under the base glaze would be the
culprit. A combination of the new clay and the raw oxides may be the
problem. Nonetheless, putting them on the outside of the base glaze is not
doable (if you ever take a jaunt from Steamboat to Estes Park, stop in at
Earthwood Artisans and you'll see why I can't do it).

One guy who e-mailed privately said he had the same problem with pinholing
after a new clay change, using Hansen's base. He added 1.25% Lithium to his
base and the problem went away. What do you think about that?

The white bodies I tried from Tucker didn't seem to pinhole. Changing to a
white body now is not something 100 wholesale customers would appreciate I'm
sure, so I'd have to figure out how to make a 180 in mid-stream without
losing existing customers. I'm certainly not smart enough to figure out
that marketing/sales pretzel.

Could the manganese be causing any problems?

Thanks much for your help.

Ken Russell
The Russell Pottery

dayton j grant on mon 5 feb 01


somebody told me that if you bisque at 04 or even 03 (a nice high bisque
) that it would decrease the incidence of pinholing and if all else fails
just fire higher and higher until the glaze smooths out (just guessing)
________________________________________________________________
GET INTERNET ACCESS FROM JUNO!
Juno offers FREE or PREMIUM Internet access for less!
Join Juno today! For your FREE software, visit:
http://dl.www.juno.com/get/tagj.

dayton j grant on mon 5 feb 01


ken if you use soldate 60 mixed at varying intervals with cedar heights
earthenware you can make a claybody that is really durable and will
vitrify at any temp you like depending on the ratio of earthenware and
stoneware then you will be aware of the max temp for your bisque ...and i
dont really know for sure but someone told me that "soaking"dosent do
anything but use more fuel ... for the sake of effficiency the temp
should always be going up(fuel)or down (no fuel)
________________________________________________________________
GET INTERNET ACCESS FROM JUNO!
Juno offers FREE or PREMIUM Internet access for less!
Join Juno today! For your FREE software, visit:
http://dl.www.juno.com/get/tagj.

TUCKERS on tue 6 feb 01


Hi Ken,
Sorry to hear you're having this trouble, but pinholing isn't usually =
too big a deal to fix.
I've forwarded your post directly to Ron Roy so you'll probably hear =
from him as well, but a typical answer to this problem is:

Pinholing is caused because there was insufficient off-gasing in the =
bisque firing, hence there are materials that are trying to get out of =
the clay during the glaze firing. Your glaze is melting and slowing =
down the gases from escaping the clay, leaving these little bubbles and =
blisters.

The solutions are:
1./ try to do a better job of getting the gases out in the bisque.
2/ try to keep the glaze liquid longer.

Number 1 is generally accomplished by bisquing higher and slower -try =
only going 100F per hour from about 1300 or 1400 F to the end of the =
bisque (carbon burns out in this range), and try bisquing to about ^04 =
instead of ^05. Some people don't like to bisque too high because it =
changes how they have to apply glaze - my wife only bisques ^6 clay to =
^08, but she never goes faster than 100F per hour from about 1300F to =
the end.
Number 2 is accomplished by soaking longer - a 10 minute soak at the end =
of a glaze firing doesn't do anything - try soaking for closer to 30 =
minutes to allow the glaze to better heal over these little sores.


If any of these suggestions concern you, or you have other comments to =
share, please don't hesitate to contact me directly at either:
Tuckers@passport.ca or 1-800-304-6185.

I'm glad to hear that in other respects you are happy with the clay.

Michael Leonard
General Manager.
Tucker's Pottery Supplies



-----Original Message-----
From: Ken Russell [SMTP:gone2pot@ISPCHANNEL.COM]
Sent: Friday, February 02, 2001 11:05 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Pinholing

I have a pinhole problem and can't figure out what I'm doing wrong. =20

My clay is Tucker MidCal5 w/ mang. I apply cobalt, black copper, =
manganese, or chrome/cobalt wash to pots for under glaze color just =
after throwing.

My bisque fire schedule is:
0-200 rate 100F/hr hold 3.5 hours (for candling)
200-1000F rate 175/hr hold 0.0
1000-1891 rate 150/hr hold 0.0

Glaze is Hansen Cone 5 Base w/4% Zircopax, 1% Tin Ox

Hansen Base:

20% Silica (325)
20% Custer (325)
20% Wollastonite
20% 3134
20% China Clay (sometimes I use EPK when I can't get the English China =
Clay)

Glaze fire schedule:

0-250 @100F/hr Hold 0
250-1000F @ 250/hr Hold 0
1000-1300F @ 150/hr Hold 0
1300-1685F @ 180/hr Hold 0
1685-2199 @ 80/hr Hold 10 minutes

I fire in 5 KM1227's all ITC 100 coated. =20

The pin holes are worse (read lots on pinholes per square inch) under =
cobalt oxide, not as bad under black copper and much less on the plain =
base glazed areas. The pin holes are all VERY, VERY tiny but =
noticeable. My old clay body was Continental MidRange w/ mang and I =
didn't have any pinholing problems at all using the same firing =
schedules and base glaze. However, other things required me to change =
clay bodies. The clay is superior to anything I've ever used in the =
past in every aspect except for this weird tiny pinholing.

Any help with firing schedules, base glaze suggestions would be =
appreciated.

Ken Russell
The Russell Pottery
gone2pot@ispchannel.com

_________________________________________________________________________=
_____
Send postings to clayart@lsv.ceramics.org

You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/

Moderator of the list is Mel Jacobson who may be reached at =
melpots@pclink.com.

Randy McCall on tue 30 may 06


Thanks Ron

I am going to try your suggestions on the next bisque fire probably later in
the week.

I am going to

Turn on bottom low switch for an hour
middle low switch for an hour
top low switch for an hour

All switches on medium for six hours

Bottom switch on high, middle switch on medium, and top switch on high until
Cone 04. Any other suggestions you can think of is welcome.


I still have the feeling it may be in my materials. When I fired the test
tubes most of the tubes were on the same shelf. The commercial glazes did
not pinhole but the main two that did pinhole had 6% rutile.

I am going with your suggestions first to try to eliminate the bisque area.

Will let you know the results after the glaze fire.

Thanks for all your help.................


Randy
South Carolina
Pottery Web site

http://members.tripod.com/~McCallJ/index.html

Carol Tripp on wed 31 may 06


Hi Pat,
Dang those pinholes - I seemed to have a problem with the insides of bowls
not healing over and certain high alkaline glazes always pinholed. But then
I changed my fire-down to go really slooow after the top temp and soak. I
have the kiln going at 25C/hour down for two hours after the top and soak
and this seems to have solved my pinhole difficulties on all surfaces and
with all glazes. Plus, the glazes look really well melted - almost like
they have lead in them, which they don't. I have had to lower my top temp
and shorten the soak because the 25C/hour firedown seems to promote more
heatwork and I'd be overfiring if I didn't compensate. So, how clear is
this? Just watch your cones and jump forward to the next ramp to start the
fire down.
Best regards,
Carol
Dubai

Pat wrote, in part:
>An observation,
>When re firing vertical surfaces at 1260 * they seem to be o.k. When
>refiring convex surfaces, they pinhole -- ??
>Is it to do with the glaze failing to stretch over the curve??
>And would it be cured by a higher second firing ?
>

_________________________________________________________________
Express yourself instantly with MSN Messenger! Download today it's FREE!
http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/

Ron Roy on wed 31 may 06


HI Pat,

Sounds like your glaze needs a little more melt.

The reason pinholes seal over on vertical surfaces - the glazes slides down
a bit and helps heal over any holes.

Horizontal surfaces mean no gravity effect so holes take longer to seal over.

RR


>An observation,
>When re firing vertical surfaces at 1260 * they seem to be o.k. When
>refiring convex surfaces, they pinhole -- ??
>Is it to do with the glaze failing to stretch over the curve??
>And would it be cured by a higher second firing ?
>
>I am asking before I reprogramme the kiln because that is a major stress
>situation !
>Any theories welcolmed,
>Pat Southwood.

Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0

Pat Southwood on wed 31 may 06


An observation,
When re firing vertical surfaces at 1260 * they seem to be o.k. When =
refiring convex surfaces, they pinhole -- ??
Is it to do with the glaze failing to stretch over the curve??
And would it be cured by a higher second firing ?

I am asking before I reprogramme the kiln because that is a major stress =
situation !
Any theories welcolmed,
Pat Southwood.
Just recovering from the best Open Studios yet.

Edouard Bastarache on mon 5 dec 11


A good checklist

Cures for pinholing according to Robin Hopper:

1-lenghten the firing cycle,
2-apply the glaze less thickly,
3-add more flux to the glaze to make it more fluid,
4-decrease the content of zinc or rutile,
5-where zinc is used, try calcining half of the zinc content,
6-increase the maturing temperature of the glaze,
7-hold the kiln at the maturing temperature for a soaking
period of up to 4 hours,
8-cool the kiln slowly.
(The Ceramic Spectrum)

Gis,

Edouard Bastarache
Spertesperantisto

Sorel-Tracy
Quebec

http://www.flickr.com/photos/30058682@N00/
http://edouardbastarache.blogspot.com/
http://edouardbastaracheblogs2.blogspot.com/
http://www.facebook.com/edouard.bastarache

Mike Gordon on fri 25 may 12


Aside from the other suggestions made about slow bisque,etc. I solved
my pinhole problems that were occurring at the lower parts of pots that
had been trimmed. I would wet the area with a wet sponge and use a
metal rib to go over the area that had been trimmed. No more pin holes.
Mike Gordon

tony clennell on sat 26 may 12


Mike: I guess that's better than pinholing but it would take all the
expression out of the trimming. I use trimming to add some more gesture to
my pots. The whoppee or circle of life that I so like on the footring would
not like to be sponged or ribbed.
But, if it were pinholing and I couldn't sell them I think I switch clays,
soak or do something other than sponge and scrap. I usually smack students
that sponge their pots.
cheers,
Tony

On Fri, May 25, 2012 at 2:29 PM, Mike Gordon wrote:

> Aside from the other suggestions made about slow bisque,etc. I solved
> my pinhole problems that were occurring at the lower parts of pots that
> had been trimmed. I would wet the area with a wet sponge and use a
> metal rib to go over the area that had been trimmed. No more pin holes.
> Mike Gordon
>



--


http://smokieclennell.blogspot.com

Edouard Bastarache on sun 27 may 12


A good checklist

Cures for pinholing according to Robin Hopper:

1-lenghten the firing cycle,
2-apply the glaze less thickly,
3-add more flux to the glaze to make it more fluid,
4-decrease the content of zinc or rutile,
5-where zinc is used, try calcining half of the zinc content,
6-increase the maturing temperature of the glaze,
7-hold the kiln at the maturing temperature for a soaking
period of up to 4 hours,
8-cool the kiln slowly.
(The Ceramic Spectrum)

Plejkore,

Edouard Bastarache=3D20
Spertesperantisto=3D20

Sorel-Tracy
Quebec

http://www.flickr.com/photos/30058682@N00/
http://edouardbastarache.blogspot.com/
http://smart2000.pagesperso-orange.fr/bloggs_edouard.htm
http://www.facebook.com/edouard.bastarache

Lee on sun 27 may 12


On Sat, May 26, 2012 at 7:51 AM, tony clennell wr=
=3D
ote:

> But, if it were pinholing and I couldn't sell them I think I switch clays=
=3D
,
> soak or do something other than sponge and scrap. I usually smack student=
=3D
s
> that sponge their pots.

Terra sig works.

A Mungyeong pot, nicely crawled on the foot (they go to great lengths
to "achieve" this "fault":

http://bit.ly/JnNteZ

I traded this Ki-seto winter bowl for the Ido bowl above:

http://bit.ly/LrYXlC


--
=3DA0Lee Love in Minneapolis
http://mingeisota.blogspot.com/

=3DA0"Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=3D9=
7that is, =3D
"The
land of eternal youth is behind the house, a beautiful land fluent
within itself." -- John O'Donohue