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Chemistry basics for potters?



 
 
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  #11  
Old October 9th 07, 12:31 PM posted to rec.crafts.pottery
Bubbles_
external usenet poster
 
Posts: 81
Default Chemistry basics for potters?


"DKat" wrote in message
...
The first thing I would have recommended you do is to go to these sites
and

- snip loooong list of wonderful links and suggestions -

While I really like this room it is for the most part relatively quiet
(one of the reasons I like it). I think you would do better posting your
questions in the other room. They have first class support there who
check in regularly.


I also appreciate this room because it is quiet. As you might have noticed,
I don't stop in very often these days, so the fewer things to catch up with,
the better. Also, because it is a newsgroup, I can mark threads to ignore or
follow, and I can view only new posts. That way, it is wayyyy simpler to get
caught up with what interests me.

P.S. I checked the site where you get your glaze and clay and still have
not been able to figure out what is what. They are not going to share the
recipe of their glazes however so there is no way to help with the
chemistry of your glazes. It would be good to know if you are underfiring
your glaze but I can't find it from what you gave us. As I said however,
any commercial glaze should not be giving you this problem if you are
firing to the correct temperature.


I am firing the glazes to the temperature ranges required by the
manufacturer, so the problem doesn't lie there. I've added a little "ps" to
my bubbling post, as I had a thought that aluminium might cause the
problem - or at least make it worse.

I have also talked with my clay/glaze supplier, and have tried his
suggestions without luck. But I had a couple of pots a couple of years ago
that also bubbled badly - and he refired them at a slightly higher
temperature and they turned out wayyyy better. I try the same here, and I
have no luck - so it could also be something with my kiln - maybe it is too
small so that the circulation is bad? I dunno. I'm running out of ideas and
getting more and more pretty pieces that are impossible to use :-(

Hope you are well from that flu you had and happily jumping around doing
your things again!

Marianne


Ads
  #12  
Old October 9th 07, 01:29 PM posted to rec.crafts.pottery
Bob Masta
external usenet poster
 
Posts: 96
Default Chemistry basics for potters?

On Tue, 9 Oct 2007 13:09:02 +0200, "Bubbles_"
wrote:

Is there a table anywhere on the internet that shows the Celcius scale next
to the cone scale? I read cone this and cone that and still don't have a
clue what temp they are - and the cone 6 and cone 06 stuff is really
confuzzling!


The best source for this sort of information that I know of comes from
Orton, who manufacture the cones most USA potters use. If you
go to this page
http://www.ortonceramic.com/resources/
you'll find Wall Charts on the right side of the page. These are in
PDF format for you to print out. By Googling for "Orton Cone Celsius"
I found
www.nmclay.com/Kilns/coneCchart.htm
which is a browser-friendly version.

Note that you must pay careful attention to heating rate when
you use these cone-to-Celsius conversions. There is a column for
the degrees per hour for the last 90-120 minutes of firing (or
whatever your chart says). You'll notice that for any given cone,
the corresponding temperature is lower for the slower heating
rates, since there is more time for the heat to work on the clay.

I tend to use the 15C/hour rate, occasionally 60C/hr.
I haven't looked at the latest Orton chart, but the one from nmclay
above doesn't have a 15C/hour rate, just 60 and 150. If your kiln
is topping out near the cone temperature, the heating rate will be
much slower than 60... and in fact a slow rate is probably what you
want anyway, if your goal is to avoid bubbling. So if the wall chart
on the Orton site no longer has this rate, let me know and I will
see if I still have an old file around.

There has been a series called "Back To Basics" by Pete Pinnell
running in Clay Times. The latest installment (Part 4) is called
"Making Sense of Unity Formulas". Covers the bascis well,
and gives good advice.


I am assuming that Clay Times is an American publication? It would cost me a
fortune to get hold of issues of that. I do subscribe to the British
magazine Ceramic Review, though, and that has had some seemingly good
articles, but, as I said above, my knowledge is wayyyy to lacking as yet.

The big problem is that it's a long way from normal chemistry
to understanding what will make a glaze stiff or runny, glossy
or matte, etc. Most of this comes down to us as "rules of thumb"
which, although they do have a scientific basis, may be better
than trying to figure things out from scratch. There are just
too many variables, especially when you include the firing
schedule, to do any serious prediction "de novo". But once
you have a starting point, it is much easier to say "keeping
everything else the same, more alumina will make this glaze
less runny", or whatever.


I do get what you mean, but then I would be winging it and not able to
understand a little of WHY those substances do what they do. And that would
mean that I would have less intuition about what else I could try to achieve
what I want.


Sorry, what I meant to imply is that it's probably not reasonable to
expect to be able to look at a recipe and predict all its fired
properties. It's worthwhile to develop an intuition of the
"character" of each of the players, so that you'll know which ones to
add more or less of when you want to change a recipe. The books
are good for that. But it isn't really very much like "chemistry",
in the sense that you don't find precise formulas like you might
for a standard compound. In pottery we are dealing with *mixtures*,
and we are interested in melting points (among other things).
These don't come down to neat answers; instead the best you can
hope for is eutectic melting graphs for a couple of components,
which are pretty useless when you have many more than that.
So we use the Unity Formula instead, which is numerical but it's
more like a starting point for you to make adjustments from.

Best regards,


Bob Masta

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Signal Generator
Science with your sound card!
  #13  
Old October 9th 07, 05:06 PM posted to rec.crafts.pottery
DKat
external usenet poster
 
Posts: 141
Default Chemistry basics for potters?

Sorry about top posting but I just don't buy that the other is more polite -
if you haven't kept up, the old message is there for reference - otherwise
why should you have to read it all to get to where you are going... Sorry
about the rant but I have never understood the etiquette of bottom posting
(I'm not referring to your proper behaviour by the by but my improper
behavior - so I'm not ranting at you but defending myself).

I'm all over the flu - just living with the lack of air from asthma due to
allergies (I'm really hoping it snows soon). Which makes me cranky - which
explains the above silly rant. Thanks for remembering and thinking of me.

How does this glaze behave over or under other glazes? If they have sold
you a glaze that is not maturing at the temperature they claim then bad on
them (you should not have to fire higher than what they say it fires to).
Is there a reason you are sticking with this glaze when it is behaving
badly? The reason I ask these questions is that depending on why you are
keeping this glaze and how it behaves with other glazes - there might be
short term fixes.

Donna

P.S. I also like this room better because you are more likely to get a
response (even if it is maybe more likely not to be corrected if it is
wrong) and you can easily follow threads. I hate the inability to keep a
thread together in Clayart. I posted your original question there and never
did get a response. There is quite a bit of chatter though on all sorts of
odds and ends I would never want to follow. Still, if you can at least do
searches there, I think you would find it useful and that is where you would
pick up the pearls by the experts. As it turns out really - most questions
you would ever ask have already been asked and the ones that haven't are
usually impossible to answer.


"Bubbles_" wrote in message
...

I also appreciate this room because it is quiet. As you might have
noticed, I don't stop in very often these days, so the fewer things to
catch up with, the better. Also, because it is a newsgroup, I can mark
threads to ignore or follow, and I can view only new posts. That way, it
is wayyyy simpler to get caught up with what interests me.

P.S. I checked the site where you get your glaze and clay and still have
not been able to figure out what is what. They are not going to share
the recipe of their glazes however so there is no way to help with the
chemistry of your glazes. It would be good to know if you are
underfiring your glaze but I can't find it from what you gave us. As I
said however, any commercial glaze should not be giving you this problem
if you are firing to the correct temperature.


I am firing the glazes to the temperature ranges required by the
manufacturer, so the problem doesn't lie there. I've added a little "ps"
to my bubbling post, as I had a thought that aluminium might cause the
problem - or at least make it worse.

I have also talked with my clay/glaze supplier, and have tried his
suggestions without luck. But I had a couple of pots a couple of years ago
that also bubbled badly - and he refired them at a slightly higher
temperature and they turned out wayyyy better. I try the same here, and I
have no luck - so it could also be something with my kiln - maybe it is
too small so that the circulation is bad? I dunno. I'm running out of
ideas and getting more and more pretty pieces that are impossible to use
:-(

Hope you are well from that flu you had and happily jumping around doing
your things again!

Marianne



  #14  
Old October 9th 07, 05:21 PM posted to rec.crafts.pottery
Dewitt
external usenet poster
 
Posts: 14
Default Chemistry basics for potters?

On Tue, 9 Oct 2007 12:06:42 -0400, "DKat"
wrote:

P.S. I also like this room better because you are more likely to get a
response (even if it is maybe more likely not to be corrected if it is
wrong) and you can easily follow threads. I hate the inability to keep a
thread together in Clayart.


I have my Clayart email, as well as most my other email lists, sent to
my gmail (google email) account. gmail automatically threads
conversations. I simply filter my different email lists into separate
folders. Oh, and gmail is free.

If anyone wants an invitation to get a gmail account, send my private
email and I'll send you one. Posting such a request to the group,
however, will get you scorn and ridicule. :-)

deg
  #15  
Old October 9th 07, 07:00 PM posted to rec.crafts.pottery
DKat
external usenet poster
 
Posts: 141
Default Chemistry basics for potters?

I'm real confused (again) - you just go to goggle to get a gmail account
don't you? Or are you referring to belonging to a group?

I tried having clayart emailed to me and was soon so overwhelmed with emails
that I just gave up on it. Clayart does have some mapping to threads but
they are frequently broken off depending on how people answer the posts. So
you can have dozens of threads with the exact same title. Since Clayart is
a list and not a group it behaves in a very different and archaic way than
what you now find in newsgroups.

"Dewitt" wrote in message
...
On Tue, 9 Oct 2007 12:06:42 -0400, "DKat"
wrote:

P.S. I also like this room better because you are more likely to get a
response (even if it is maybe more likely not to be corrected if it is
wrong) and you can easily follow threads. I hate the inability to keep a
thread together in Clayart.


I have my Clayart email, as well as most my other email lists, sent to
my gmail (google email) account. gmail automatically threads
conversations. I simply filter my different email lists into separate
folders. Oh, and gmail is free.

If anyone wants an invitation to get a gmail account, send my private
email and I'll send you one. Posting such a request to the group,
however, will get you scorn and ridicule. :-)

deg



  #17  
Old October 9th 07, 10:31 PM posted to rec.crafts.pottery
Dewitt
external usenet poster
 
Posts: 14
Default Chemistry basics for potters?

On Tue, 9 Oct 2007 19:10:35 +0100, Rob Morley
wrote:

It used to be you had to receive an invitation to get a Google mail
account (phased introduction of a beta product or viral marketing?) but
now you can just go there and sign up.


Didn't know that. They still have an "send invite" function on my
gmail page. It was probably viral marketing, but it worked really
well!

deg

  #18  
Old October 10th 07, 01:23 PM posted to rec.crafts.pottery
Bob Masta
external usenet poster
 
Posts: 96
Default Chemistry basics for potters?

On Tue, 9 Oct 2007 14:00:16 -0400, "DKat"
wrote:

I'm real confused (again) - you just go to goggle to get a gmail account
don't you? Or are you referring to belonging to a group?

I tried having clayart emailed to me and was soon so overwhelmed with emails
that I just gave up on it. Clayart does have some mapping to threads but
they are frequently broken off depending on how people answer the posts. So
you can have dozens of threads with the exact same title. Since Clayart is
a list and not a group it behaves in a very different and archaic way than
what you now find in newsgroups.


I finally gave up on Clayart last year, even though I was getting the
Digest format just to avoid the above-mentioned Email blizzard.
The problem is (was?) that the moderator just didn't have control
of the Listserv, and apparently nobody was really administering it
who knew what they were doing.

The kicker for me was that Clayart insisted on posting all messages to
the archives, with your Email address clearly visible to bots. So I
was getting several dozen spams a day just due to that. (I had a
separate account for Clayart, never used for anything else, so I knew
that's where they came from.) Other lists "munge" the addresses in
the archives, to make bot harvesting tougher. (Munging is where
you replace " with something like
"MyNameatMynospamHostdotcom", which any human can
figure out but is tougher for a bot.)

(As an aside, the moderator also was getting hit with
tons of spam to the list itself. This is an easy problem for a
Listserv administrator to fix, but the moderator couldn't do it
and didn't want to bother the (nominal) administrator that
was hosting the list for free. So he spent hours each day
dealing with it himself.)

Anyway, when my workload got high enough that I was no
longer willing to put up with the spam, or with wading through
personal and philosophical monologues to get to clay stuff,
I let it go. I guess I'll give it another look if and when things
calm down... maybe they will have gotten the administration
squared away by then!

Apologies for the diatribe...




Bob Masta

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Signal Generator
Science with your sound card!
  #19  
Old October 10th 07, 08:22 PM posted to rec.crafts.pottery
WJS
external usenet poster
 
Posts: 8
Default Chemistry basics for potters?

Bob and all:
Clayart is indeed going through some growing pains.
It is "owned" by the American Ceramic Society, and is being moderated
by volunteers who have absolutely NO control over what ACerS chooses to do
or not do.
in that, Bob is right. The moderators have little control, all they can do
is approve or disapprove posts to the list
make minor changes etc..
The software being used is also completely outdated. Clayart is being run
on a server
using Listserv software version 1.8, while the newest version is 18.0. That
should tell you something.

In addition, until very recently, ACerS was changing their IT staff more
often than I change socks.
Here today, POOF!, gone tomorrow...no one seemed to know what the
administration password is, etc.
But, things are looking up. There are some very dedicated experienced
volunteers working on the IT problems now,
as well as new staff at ACerS, and some progress is being made. It will get
straightened out.

Remember that Clayart is a group of potters, around 3000 of us, worldwide.
(Our latest member is a
ceramic studio/center in Cambodia, which is amazing to me.) And it's free,
so I tend to overlook a lot of the
problems in exchange for the information and world view that I receive.
Yes, there is a LOT of e-mail,
(3000 people have a tendency to do that g) and so I have learned to delete
threads in which I am not interested.
With Clayart, your delete key is your friend g.
Still, it is worth joining Clayart for the information contained in the
archives
alone, which date back over 12 years now. If you can think of a ceramic
problem, chances are you will
find the answer in the archives. If not, post the question to the list, and
you'll have your answer.

I guess I don't have to say that I'm an enthusiastic supporter. One of the
things for which I will always
appreciate Clayart is the presence of its memebers at NCECA's annual
conference (National Council on Education for the Ceramic Arts).
The conference is held yearly, a different city each year (next March it
will be in Pittsburgh Pennsylvania).
Of the 6000 attendees for the last conference held in Louisville Kentucky,
over 2500 were members of Clayart.
We had our own hotel (which sold out) for that conference
and we are also getting our own hotel (The Omni William Penn) for this one.
That says something about the power of numbers (of crazy potters g).
Not only do you get to learn from some of the largest "names" in ceramics
online with Clayart, you actually get to go meet
them, share meals, go out on the town, learn, etc..
It's more a big "family". A big, talkative family. And I am thankful to be
a part of it.

Best,
Wayne Seidl
Vice President,
Potters Council of the American Ceramic Society 2007-2008

"Bob Masta" wrote in message

I finally gave up on Clayart last year, even though I was getting the
Digest format just to avoid the above-mentioned Email blizzard.
The problem is (was?) that the moderator just didn't have control
of the Listserv, and apparently nobody was really administering it
who knew what they were doing.

The kicker for me was that Clayart insisted on posting all messages to
the archives, with your Email address clearly visible to bots. So I
was getting several dozen spams a day just due to that. (I had a
separate account for Clayart, never used for anything else, so I knew
that's where they came from.) Other lists "munge" the addresses in
the archives, to make bot harvesting tougher. (Munging is where
you replace " with something like
"MyNameatMynospamHostdotcom", which any human can
figure out but is tougher for a bot.)

(As an aside, the moderator also was getting hit with
tons of spam to the list itself. This is an easy problem for a
Listserv administrator to fix, but the moderator couldn't do it
and didn't want to bother the (nominal) administrator that
was hosting the list for free. So he spent hours each day
dealing with it himself.)

Anyway, when my workload got high enough that I was no
longer willing to put up with the spam, or with wading through
personal and philosophical monologues to get to clay stuff,
I let it go. I guess I'll give it another look if and when things
calm down... maybe they will have gotten the administration
squared away by then!

Apologies for the diatribe...
Bob Masta



  #20  
Old October 11th 07, 12:43 PM posted to rec.crafts.pottery
Bubbles_
external usenet poster
 
Posts: 81
Default Chemistry basics for potters?


"Bob Masta" wrote in message
...

The best source for this sort of information that I know of comes from
Orton, who manufacture the cones most USA potters use. If you
go to this page
http://www.ortonceramic.com/resources/


Thanks! I found one there with both C and F on it. Will print it out and
have a closer look.

-snip-

is topping out near the cone temperature, the heating rate will be
much slower than 60... and in fact a slow rate is probably what you
want anyway, if your goal is to avoid bubbling. So if the wall chart
on the Orton site no longer has this rate, let me know and I will
see if I still have an old file around.


I have tried stretching the heating rate up to top temp (1250). I have a
bunch of stuff ready for a glaze firing, and I think I will try a longer
time to top-temp this time.

-snip-

Sorry, what I meant to imply is that it's probably not reasonable to
expect to be able to look at a recipe and predict all its fired
properties. It's worthwhile to develop an intuition of the
"character" of each of the players, so that you'll know which ones to
add more or less of when you want to change a recipe. The books
are good for that. But it isn't really very much like "chemistry",
in the sense that you don't find precise formulas like you might
for a standard compound. In pottery we are dealing with *mixtures*,
and we are interested in melting points (among other things).
These don't come down to neat answers; instead the best you can
hope for is eutectic melting graphs for a couple of components,
which are pretty useless when you have many more than that.
So we use the Unity Formula instead, which is numerical but it's
more like a starting point for you to make adjustments from.


I do understand about the mixtures.What I want to achieve with my studies is
to better understand the properties of the substances I am using and better
know if I can try similar substances and know how to identify those similar
substances.

You write about maturation of the clay. The clay fires really well, as far
as I can tell. It is this darned glaze that is irritating me to bits! ;-)

Thanks Bob!

Marianne


 




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