Lois Ruben Aronow on sun 29 jul 07
How timely that this has come up.
I have been using F4 for ages in my base glaze. I called my ceramic
supplier, as the bag of F4 they recently sent me was marked "Feldspar NC4".
The told me they changed suppliers, and NC4 was what this new supplier
called F4.
I was mixing up some glaze on Friday for a commission, using the new bag of
spar. I wisely (thankfully!!) did a test before glazing up half of a very
large dinner set. I noticed that on my shelf I had kept the original test I
did (I am doing a custom color), so I threw in a shard glazed with the
original batch. I fired them next to each other on the kiln shelf.
OK, you guessed it - the new one is somewhat different, and I'm assuming it
is the spar. The only other fresh material I am using is the mason stain,
and they tend to be incredibly consistent. The original batch was more
transparent, and the new batch is more opaque, and a little paler in color.
SO......how different is NC4 from F4, and should I kick my ceramic supplier
in the ass for telling me they are the same?
I am really glad that I only need to tweak the glaze, and not remake the
work. I am also happy I buy this particular chem by the 50lb bag. Any less
and it would have had a nice label on it that said "F4", and I would have
been banging my head against the wall trying to figure out where I went
wrong. The only "bad" news is I'm on a very tight deadline.
Any and all help is appreciated.
...Lo
**********
Lois Aronow Ceramics
Brooklyn, NY
www.loisaronow.com
www.craftsofthedamned.blogspot.com
> -----Original Message-----
> From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of
> claystevslat
> Sent: Sunday, July 29, 2007 3:15 AM
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Re: NC-4/G-200
>
> Chuck --
>
> They are close, but not identical.
>
> Digital fire gives NC-4 as
>
> CaO 1.400
> K2O 4.100
> MgO 0.050
> Na2O 6.800
> Al2O3 18.850
> SiO2 68.150
> Fe2O3 0.070
>
> And G-200 as
>
> Fe2O3 0.080
> SiO2 66.300
> Al2O3 18.500
> Na2O 3.040
> K2O 10.750
> MgO 0.050
> CaO 0.810
>
> The biggest difference is in the sodium/potassium mix.
> G-200 is more potash intensive, NC-4 relies more on sodium.
>
> My (very crude) rule of thumb on this kind of sub is if the
> feldspar makes up less than 1/5 of the glaze and is more or
> less what I'm looking for, I do a 1 for 1 sub first and then
> fix it if I don't like the outcome on a test. If it's more
> than that, I will try to correct up-front.
>
> Remember all feldspars are subject to minor changes in
> composition. Except for the K/Na, I wouldn't expect the
> differences to be significant in most glazes ...
> but the Li-rich glazes I've been experimenting with of late
> are all 'tippy' and a change of 1/2 of a percent in anything
> -- even silica -- will change the glaze appearance (and,
> possibly, durability).
>
> Good luck -- I'd be interested to know how things turn out --
> Steve Slatin
>
> --- In clayart@yahoogroups.com, Chuck Wagoner wrote:
> >
> > Great information basin of Clayart,
> >
> > Could someone confirm for me that NC-4 feldspar is equal to G-200?
> I have
> > two bags of it and would like to use it.
> >
> > We can dig up a lot of clay here in Indiana, but no feldspar in my
> back
> > yard.
> >
> > Thank you,
> >
> > Chuck
>
> ______________________________________________________________
> ________________
> 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.
John Hesselberth on mon 30 jul 07
On Jul 29, 2007, at 5:03 PM, Lois Ruben Aronow wrote:
> SO......how different is NC4 from F4, and should I kick my ceramic
> supplier
> in the ass for telling me they are the same?
Hi Lois,
If your supplier had said they are "close, but test" he probably
wouldn't deserve a kick, but I vote for giving him one. The analyses
I have says NC4 has 1% less K2O, almost 1% less Al2O3, and 2% more
silica. Other oxides are much closer. But given that we are dealing
with ground up rocks it is not inconceivable that a new bag of F4
might vary that much also. But F4 and NC4 may also be ground to a
different mesh size or have other impurities that could affect their
behavior in a glaze. If the feldspar is a minor component in your
glaze you probably would never see the difference. If it is a major
component you might. You were very wise to test first.
I have been hearing off an on for a year or so that F4 is no longer
available. But that is often what our suppliers say when they change
suppliers themselves. It may not be that it is not available--it may
just be that the price went up and they have decided to substitute
something cheaper. Does anyone have any "from the horse's mouth"
information on availability of F4?
John Hesselberth
www.frogpondpottery.com
"Man is a tool-using animal....without tools he is nothing, with
tools he is all" .... Thomas Carlyle
Lois Aronow on mon 30 jul 07
My supplier - the despicable Ceramic Supply of NY/NJ told me it was the
same, just a different name. I tested first because it is for a large,
expensive custom dinner set. I worked with the client for a long time
to develop some colors I don't usually do. sent them chips and
everything. It is personally important to me because it is a colorway I
generally run like hell from, but i really think this is going to be
spectacular, and may be a new direction for me. It really is a
testament to working side-by-side with a customer.
I would love to give myself a pat on the back (maybe I deserve one
anyway) because I kept the original glaze tests and compared them to the
new batch. I did't glaze the pots with the new batch, in part because i
am just really busy now. I chalk it up to luck, but maybe I have
learned something after all these years ;-)
Is the feldspar really a small component if it is 47% of the glaze?
Anyhow, I'm doing another round of testing today, with fingers crossed,
and several different bases.
John, I do have pics if you're interested.
----- Original Message -----
From: John Hesselberth
Date: Monday, July 30, 2007 8:46 am
Subject: Re: NC-4/G-200 - also Kona F4 question
To: CLAYART@LSV.CERAMICS.ORG
> On Jul 29, 2007, at 5:03 PM, Lois Ruben Aronow wrote:
>
> > SO......how different is NC4 from F4, and should I kick my ceramic
> > supplier
> > in the ass for telling me they are the same?
>
> Hi Lois,
>
> If your supplier had said they are "close, but test" he probably
> wouldn't deserve a kick, but I vote for giving him one. The analyses
> I have says NC4 has 1% less K2O, almost 1% less Al2O3, and 2% more
> silica. Other oxides are much closer. But given that we are dealing
> with ground up rocks it is not inconceivable that a new bag of F4
> might vary that much also. But F4 and NC4 may also be ground to a
> different mesh size or have other impurities that could affect their
> behavior in a glaze. If the feldspar is a minor component in your
> glaze you probably would never see the difference. If it is a major
> component you might. You were very wise to test first.
>
> I have been hearing off an on for a year or so that F4 is no longer
> available. But that is often what our suppliers say when they change
> suppliers themselves. It may not be that it is not available--it may
> just be that the price went up and they have decided to substitute
> something cheaper. Does anyone have any "from the horse's mouth"
> information on availability of F4?
>
> John Hesselberth
> www.frogpondpottery.com
>
> "Man is a tool-using animal....without tools he is nothing, with
> tools he is all" .... Thomas Carlyle
>
>
______________________________________________________________________________
> 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.
John Hesselberth on mon 30 jul 07
On Jul 30, 2007, at 10:23 AM, MissLo@nyc.rr.com wrote:
> Is the feldspar really a small component if it is 47% of the glaze?
No, that is really large. You need to be very careful when buying
feldspar. Might want to buy a lifetime supply when you find what you
like. 10% or less is small in my way of thinking.
Below is what Tony Hansen has on his web site regarding these two
materials. Doesn't sound like the person(s) who wrote those
paragraphs thought they were identical. But maybe Ron Roy or Craig
Martell who know far more about feldspars than I will chime in with
some additional info.
> NC-4 feldspar is a high quality sodium / potassium / calcium
> aluminum silicate ground to 170, 200 and 250 mesh, for ceramic
> applications. Carefully beneficiated and controlled for quality,
> NC-4 feldspar offers high alkali content and low iron oxide content
> per unit of alumina. Its various grinds are tailored for specific
> applications
> This material (F4) is prized as a porcelain ingredient because of
> its low iron content. It is used in casting and throwing porcelains
> of all types. At cone 6 for example, it is possible to make a
> vitreous body using 50-60%. However to get enough plasticity in
> such bodies, it is necessary to use ball clay or bentonite which
> can darken the color. If high plasticity is not essential, Macaloid
> and plastic kaolins can be used.
John
John Hesselberth
www.frogpondpottery.com
"Man is a tool-using animal....without tools he is nothing, with
tools he is all" .... Thomas Carlyle
Craig Martell on mon 30 jul 07
Lois was saying:
>My supplier - the despicable Ceramic Supply of NY/NJ told me it was the
>same, just a different name.
Hello Lois:
All I can say about the above is the ever colloquial; Bullshit! My
analyses confirm what John H. has already said so all I will add is that
the Si/Al ratio is important too and f-4 is: 5.79/1.0 and NC4 is:
6.24/1.0. This would normally mean that a direct sub using NC4 would give
a brighter, glassier melt but since NC4 is lower in KNaO this is not the case.
I don't know if F-4 is totally gone from the market but I can't seem to get
it any longer. I've found from analyses and fusion buttons that Unispar
50, a soda spar from Unimin Specialty Minerals, Spruce Pine, NC is damn
near identical to Kona F-4. I've done direct subs in 3 different glazes
with excellent results.
regards, Craig Martell Hopewell, Oregon
claystevslat on mon 30 jul 07
Lois --
NC-4 is this -- at least in theory.
CaO 1.400
K2O 4.100
MgO 0.050
Na2O 6.800
Al2O3 18.850
SiO2 68.150
Fe2O3 0.070
F-4 is this -- same caveat.
CaO 1.700
K2O 4.800
MgO 0.050
Na2O 6.900
Al2O3 19.600
SiO2 66.800
Fe2O3 0.040
They are much closer than NC-4 and G-200
are, and should be generally substitutable.
Of course if they are very prominent in a
glaze, the difference in Si:Al (and concentrations
of the two ions) could be significant.
It's always hard to tell when comparing
a clearer glaze with a less transparent
one what the difference is. If you have
a loupe or other magnifier, get the test
pieces together and get a good light and
check them out. Are the surfaces similar,
or is the more opaque one less regular,
possibly with a superficially reticulated
surface? This can 'dull down' a color and
make a glaze less transparent.
In my experience, this can result from a
change in the Si:Al ratio.
Another possibility worth looking at is the
prevalance of bubbles in the glaze. (They
can also dull down a color and opacify a
bit.) This is often related to LOI, with
more lossy materials being more bubbly, and
in this case it seems your more lossy test
was the more glossy, so it's unlikely that
loss is an issue. Particle size can be an
issue, but I have very little experience
with these frits and have used only one bag
each, so I don't know how consistent they
may be. I do know that NC-4 is used comercially
in different grinds. What fineness is specified
on the bag? Similar to your F-4?
Sorry I can't help more with this. Even if
you have a matching bag, though, sometimes the
contents will differ enough for this kind of
a change.
Best wishes -- Steve Slatin
--- In clayart@yahoogroups.com, Lois Ruben Aronow wrote:
>
> How timely that this has come up.
>
> I have been using F4 for ages in my base glaze. I called my
ceramic
> supplier, as the bag of F4 they recently sent me was
marked "Feldspar NC4".
> The told me they changed suppliers, and NC4 was what this new
supplier
> called F4.
>
> I was mixing up some glaze on Friday for a commission, using the
new bag of
> spar. I wisely (thankfully!!) did a test before glazing up half of
a very
> large dinner set. I noticed that on my shelf I had kept the
original test I
> did (I am doing a custom color), so I threw in a shard glazed with
the
> original batch. I fired them next to each other on the kiln shelf.
>
> OK, you guessed it - the new one is somewhat different, and I'm
assuming it
> is the spar. The only other fresh material I am using is the mason
stain,
> and they tend to be incredibly consistent. The original batch was
more
> transparent, and the new batch is more opaque, and a little paler
in color.
>
>
> SO......how different is NC4 from F4, and should I kick my ceramic
supplier
> in the ass for telling me they are the same?
>
> I am really glad that I only need to tweak the glaze, and not
remake the
> work. I am also happy I buy this particular chem by the 50lb
bag. Any less
> and it would have had a nice label on it that said "F4", and I
would have
> been banging my head against the wall trying to figure out where I
went
> wrong. The only "bad" news is I'm on a very tight deadline.
>
> Any and all help is appreciated.
>
> ...Lo
Cindy Bracker Sturm on tue 7 aug 07
I would second John's vote for a kick.
NC-4 is a Resco product (parent compay of Cedar Heights - the same =20
company that mines Redart, Goldart and the like) Kona F-4 is from =20
Hammill & Gillespie, the US importer of Grolleg etc. Bracker's just =20
got 3 skids of Kona in May and there was no information about it =20
being discontinued at that time. We carry both because they are =20
different enough to make a difference in a glaze or clay body. We =20
also carry both Custer AND G-200 in the potash feldspar category for =20
the same reason.
Personally, I can't imagine a supplier making a substitution of any =20
kind without first contacting the customer to discuss it!
Sorry for the delay in response. I took 2 days off work last week to =20=
do a home improvement project. I still don't understand how 2 days =20
off takes 2 weeks to make up for! :)
Cindy Bracker Sturm
Bracker's Good Earth Clays, Inc.
Celebrating 25 years of helping potters!
888-822-1982 =95 http://www.brackers.com
Clay Ain't Dirt!
Since June 28th, 1982
On Jul 30, 2007, at 10:25 AM, clayart@yahoogroups.com wrote:
> 10.1.
> Re: NC-4/G-200 - also Kona F4 question
>
> Posted by: "John Hesselberth" hesselberth@MINDSPRING.COM
>
> Mon Jul 30, 2007 5:55 am (PST)
>
> On Jul 29, 2007, at 5:03 PM, Lois Ruben Aronow wrote:
>
> > SO......how different is NC4 from F4, and should I kick my ceramic
> > supplier
> > in the ass for telling me they are the same?
>
> Hi Lois,
>
> If your supplier had said they are "close, but test" he probably
> wouldn't deserve a kick, but I vote for giving him one. The analyses
> I have says NC4 has 1% less K2O, almost 1% less Al2O3, and 2% more
> silica. Other oxides are much closer. But given that we are dealing
> with ground up rocks it is not inconceivable that a new bag of F4
> might vary that much also. But F4 and NC4 may also be ground to a
> different mesh size or have other impurities that could affect their
> behavior in a glaze. If the feldspar is a minor component in your
> glaze you probably would never see the difference. If it is a major
> component you might. You were very wise to test first.
>
> I have been hearing off an on for a year or so that F4 is no longer
> available. But that is often what our suppliers say when they change
> suppliers themselves. It may not be that it is not available--it may
> just be that the price went up and they have decided to substitute
> something cheaper. Does anyone have any "from the horse's mouth"
> information on availability of F4?
John and Judy Hesselberth on tue 7 aug 07
On Aug 7, 2007, at 2:55 PM, Cindy Bracker Sturm wrote:
> Bracker's just got 3 skids of Kona in May and there was no
> information about it being discontinued at that time. We carry
> both because they are different enough to make a difference in a
> glaze or clay body
Thanks for chiming in Cindy. You gave us exactly the kind of "horse's
mouth" info I was hoping for. For those who haven't met Cindy, she
and Bracker's are one of the best suppliers around. They know their
stuff and give straight answers. They are also great Clayart friends.
Regards,
John
| |
|
