Daniel Sommerfeld on thu 23 aug 07

Ivor,

I have tried this with various copper carbonate based glazes and engobes.
I usually work with oribe or a glaze called "water blue" when I want this
to occur. I will try to get some images posted better illustrating this
effect.

Thanks,

Dan Sommerfeld
www.byhand.us

Ivor and Olive Lewis on fri 24 aug 07

Dear Daniel Sommerfeld,=20

Thank you for the information about your glaze.

I have great difficulty accepting that some of the compounds we use are =
able to volatilise so readily when their melting points are in the same =
temperature range as our firing temperatures and their boiling points =
when they would freely give a vapour are way off the scale that we can =
measure. Pure copper metal melts at 1084 deg C and boils at 2580 deg C.

To get back to your ingredients. I think it is plausible that Basic =
Copper carbonate, double compound of Copper hydroxide and Copper =
carbonate, could dissolve in to some degree in water that was slightly =
acid. The solution which forms would then move through porous bisque. If =
it reaches the outer surface very little would be needed to create a =
pale blush of pink.

An interesting problem.

Best regards,

Ivor=20

Paul Herman on sat 25 aug 07

Steve and Ivor,

I imagine copper would volatilize at different temperatures,
depending on what glaze it's in.

Doesn't that sound reasonable, that if the copper in question is
mixed with fluxes, it would affect the way it fumes?

Looking at the melting temperature of copper metal only shows you one
thing.

best,

Paul Herman

Great Basin Pottery
Doyle, California US
http://greatbasinpottery.com


On Aug 25, 2007, at 6:11 PM, claystevslat wrote:

> I know little of this matter, but I do believe that it
> is erroneous to anticipate a direct relationship between
> volatilization temperature and boiling point. Certainly
> the effects on our pots indicates this. And the evidence
> of our senses at the temperatures where our bodies can
> survive shows that volatilization generally exists in
> some extent even well below boiling temperatures. That's
> why it's so easy to smell melting solids long before they
> reach their boiling temperatures.
>
> Best wishes -- Steve Slatin
>

Michael Wendt on sun 26 aug 07

It has been demonstrated repeatedly in physics classes
that liquids begin to give off molecules far below
their
boiling points. Water evaporates near freezing and
depending upon atmospheric pressure will sublime
from the solid state as well.
Reason?
Temperature in materials is a construct for our
convenience. What is actually happening is a larger
variety of molecular motions than we realize owing to
the superposition effect.
When heat is added to a mass, it increases molecular
motion similar in fashion to masses connected by
perfect
springs (springs which transmit motion without loss).
Harmonics exist that result in some waves adding,
others canceling and some at various other values.
Think of the extreme values as occasional events with
most of the motion near the middle of the bell shaped
velocity curve whose median values we assign the name
"temperature".
Now think of the odd molecule (even in a heated solid)
that is near the surface and reaches escape velocity.
All that is needed is for the sum of the vectors to
be in the correct direction and to be more than the
molecular bonding forces holding it in.
The reason it is neglected in most texts is it is too
small
to measure but with kilns and pottery, we get actual
physical proof that solids of all types exert vapor
pressure at temperatures near their melting points
at low atmospheric pressures ( for in the scheme of
things 14.7 psi is nearly a vacuum when compared
to the early earth's 500-1000 times greater pressures).
Side note:
Regarding material expansion with respect to heating
One of my physics texts (I can't find the reference
now)
explains that the ideal molecular model posits that
solid materials should not expand or contract when
heated or cooled and the theory that explains thermal
size change is also a superposition effect due to
irregular
spacings and incomplete structures that interrupt and
alter
the spacings between atoms in the molecules.
Some Lithium materials like Petalite have this
idealized
atomic radius which keeps molecular chaotic motion
to a minimum and, when mixed with the correct
proportion of Kaolin exhibit zero expansion
or contraction when heated or cooled.
Some day we may know for sure.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave.
Lewiston, Id 83501
U.S.A.
208-746-3724
wendtpot@lewiston.com
http://www.wendtpottery.com
http://UniquePorcelainDesigns.com

Timothy Joko-Veltman on sun 26 aug 07

I would add that materials do not need to be at boiling point to
become vapours. Witness water, for example. It boils at 100C, and
though my body temperature is a fairly homogenous 36.8C, I lose water
continually - especially in extremely dry weather such as we are
having here in Brasilia. So do my plants - even my ice plant, which
is cool to the touch even at midday. Another example - isopropyl
alcohol boils at 82.3C, yet we all know from experience that it
evaporates readily even in a cool room.

The Wikipedia article on Evaporation
(http://en.wikipedia.org/wiki/Evaporation) has an excellent discussion
of the phenomenon.

Regards,

Tim

Bill Merrill on sun 26 aug 07

Volatized copper does happen. Put a copper red pot next to a celadon or
base glaze with the copper red base and wallllyaaaaaaaaaaaa There is a
peach bloom effect on the pot next to the copper red pot. You can paint
raw copper on a stilt or broken piece of hard brick and control the
flashing. Try making a saggar that surrounds the pot to be fired and
paint the interior of the saggar with raw copper. You'll get a beach
bloom effect.

If you use a celadon and add a very small amount of copper to the glaze,
you can achieve a pot that is copper red and blue green and there can be
some clear where the pot wasn't reduced or the copper volatized into the
kiln. This usually happens if your burners produce a slow lazy flame.
This can be done deliberately, but the kiln will usually not be evenly
reduced due to the kiln damper belt open some during the reduction
cycle.

One of the most brilliant Copper red glazes is a "Chun " of Carlton
Ball. The formula is in his book 'Making Pottery without a wheel".
There is only 17 grams of copper in a 2000 gram batch of base. This
glaze is able to produce many different hues. All of the glazes in that
book should be tried.

These copper red glazes are called trans-mutation glazes for a reason.
They must be in a highly alkaline base glaze. Paint copper over a
hi-alumina matt glaze and a soft pink is made. Paint copper a
hi-calcium glaze a muted more muddy red is produced. The are many
exceptions and complications to reduction fired glaze work, That is part
of the charm of working the minerals, techniques or firing etc and the
results we are allowed to see.


Regards to all,

billm@pcadmin.ctc.edu

Bill Merrill 360-417-6537

=09







-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of
claystevslat
Sent: Saturday, August 25, 2007 6:12 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Diffusion through Clay Bodies? What's the right term

Ivor --

You say that you "have great difficulty accepting that
some of the compounds we use are able to volatilise so
readily when their melting points are in the same
temperature range as our firing temperatures and their
boiling points when they would freely give a vapour are
way off the scale that we can measure."

My immediate thought about that is a simple reply --
your difficulty accepting the idea appears to be
contradicted by the occasional appearance of copper
effects on pieces fired near, but not touching, copper
glazed work.

So, is it possible that the subject of volatilization
of copper has been researched, and it has been
discovered that there is volatilization of copper
significantly below the boiling point of copper?

A quick google search revealed that there has been
research on the subject, and while I would have had
to buy some expensive documents to fully research it,
some information was available free.

Karin Lundholm's doctoral dissertation on the subject
of biomass contaminants and the like, available at
www.diva-portal.org/diva/getDocument?urn_nbn_se_umu_diva-1132-
2__fulltext.pdf (p. 33) appears to show quite a bit
of copper volatilization in the range of 500 C to 900 C.

(Of course she is dealing in large part with Copper Chromate
Arsenate as 'feedstock' for the reaction.) It does, however,
appear that copper is rather volatile at temperatures
significantly lower than the boiling point of the
metal.

I know little of this matter, but I do believe that it
is erroneous to anticipate a direct relationship between
volatilization temperature and boiling point. Certainly
the effects on our pots indicates this. And the evidence
of our senses at the temperatures where our bodies can
survive shows that volatilization generally exists in
some extent even well below boiling temperatures. That's
why it's so easy to smell melting solids long before they
reach their boiling temperatures.

Best wishes -- Steve Slatin








--- In clayart@yahoogroups.com, Ivor and Olive Lewis
wrote:
>
> Dear Daniel Sommerfeld,
>
> Thank you for the information about your glaze.

________________________________________________________________________
______
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.

claystevslat on sun 26 aug 07

Ivor --

You say that you "have great difficulty accepting that
some of the compounds we use are able to volatilise so
readily when their melting points are in the same
temperature range as our firing temperatures and their
boiling points when they would freely give a vapour are
way off the scale that we can measure."

My immediate thought about that is a simple reply --
your difficulty accepting the idea appears to be
contradicted by the occasional appearance of copper
effects on pieces fired near, but not touching, copper
glazed work.

So, is it possible that the subject of volatilization
of copper has been researched, and it has been
discovered that there is volatilization of copper
significantly below the boiling point of copper?

A quick google search revealed that there has been
research on the subject, and while I would have had
to buy some expensive documents to fully research it,
some information was available free.

Karin Lundholm's doctoral dissertation on the subject
of biomass contaminants and the like, available at
www.diva-portal.org/diva/getDocument?urn_nbn_se_umu_diva-1132-
2__fulltext.pdf (p. 33) appears to show quite a bit
of copper volatilization in the range of 500 C to 900 C.

(Of course she is dealing in large part with Copper Chromate
Arsenate as 'feedstock' for the reaction.) It does, however,
appear that copper is rather volatile at temperatures
significantly lower than the boiling point of the
metal.

I know little of this matter, but I do believe that it
is erroneous to anticipate a direct relationship between
volatilization temperature and boiling point. Certainly
the effects on our pots indicates this. And the evidence
of our senses at the temperatures where our bodies can
survive shows that volatilization generally exists in
some extent even well below boiling temperatures. That's
why it's so easy to smell melting solids long before they
reach their boiling temperatures.

Best wishes -- Steve Slatin








--- In clayart@yahoogroups.com, Ivor and Olive Lewis
wrote:
>
> Dear Daniel Sommerfeld,
>
> Thank you for the information about your glaze.

Ivor and Olive Lewis on mon 27 aug 07

Dear Steve Slatin,

All solids and liquids are able to discharge atoms or molecules from =
their surfaces. But the degree to which this will happen depends on two =
functions, temperature and pressure.

Perhaps "Volatility" is about a spontaneous event, like the evaporation =
of Ether, Ethanol or Vinegar when the cap is taken from the container !

If you wish to investigate the behaviour of Copper compounds via a =
practical test you have to isolate the variable that you are monitoring =
from all other influences. This cannot be done in an active pottery =
kiln. There are ingredients in some glazes that decompose as they are =
heated and are prone to "Spitting". As I recall, one culprit is Gerstley =
Borate. So a spitting glaze could convey Copper oxide or Copper =
Carbonate into the breeze to settle on other surfaces. This effect can =
be eliminated by putting pure samples of Copper compounds on an inert =
carrier and placing these close to, say ten millimetres, but not in =
contact with a glaze sample,=20

Boiling point is governed by two variable factors, Temperature and =
Pressure. Except for daily variations and alterations in altitude we =
accept that pressure remains almost constant with time. But the lower =
the pressure the lower the temperature at which volatilisation will =
happen. You will find factors for "Vapour Pressure" in reference texts. =
For example, at a pressure of 0.2 kilo-newtons per square metre Copper =
will boil at 1667 Deg Celsius. At a pressure of 101.3 Kn/m^2 the =
temperature of 2582 deg C.

I am not sure what I would experience were I to hold my nose over pots =
of molten copper, lead, zinc or silver except the chance of breathing =
some very noxious fumes from Sodium Boro-Fluoride fluxes. But I am =
almost certain there is no metallic Copper being formed in the glazes I =
use that contain copper compounds. The melting points of copper oxides =
are higher than the MP of metallic Copper.

I accept that people will believe solids can spontaneously evaporate. =
This can be observed on the western prairies when the Chinook comes in =
from the west and snow ablates. But that is not a good model on which to =
base an analogy for glaze behaviour.

Best regards,

Ivor Lewis.
Redhill,
South Australia.

Ivor and Olive Lewis on mon 27 aug 07

Dear Paul Herman,

Nothing wrong with using your imagination. As I point out to Steve =
Slatin, some glazes are notorious for their ability to Spit, a topic =
that has been aired over these pages in the past.

Materials evaporate according to the pressure within the vessel that =
contain them as well as their temperature.

A classic demonstration in Physics was to have flask containing water =
connected to a vacuum pump. A thermometer bulb was immersed in the water =
and the flask was connected to a barometer. The water was brought up to =
the boil. Temperature and Pressure were noted. The flask was then =
allowed to cool and the vacuum pump activated. Temperature and pressure =
within the flask were recorded whenever boiling behaviour was observed. =
It was possible to have the water boiling when it was lukewarm at a =
pressure of about one fifth of an atmosphere.

Best regards,

Ivor and Olive Lewis on tue 28 aug 07

Dear Michael Wendt,=20

I think Ice will sublime when the relative humidity of the air at =
ambient pressure is exceptionally low. The reverse is also true, that =
ice will form in the air if the humidity is high and ambient temperature =
is below 0 deg C .

As I recall, the original question was about a copper colour developing =
on the outside of a vase that had a copper glaze on the inside and a =
plain glaze on the outside.

You say "One of my physics texts (I can't find the reference now) =
explains that the ideal molecular model posits that solid materials =
should not expand or contract when heated or cooled and the theory that =
explains thermal size change is also a superposition effect due to
irregular spacings and incomplete structures that interrupt and alter =
the spacings between atoms in the molecules. "..... and I thought the =
energy that we supply as heat caused the electrons to race a lot faster =
and therefore occupy more space !

Best regards,

Ivor

Ivor and Olive Lewis on tue 28 aug 07

Dear Timothy Joko-Veltman,=20

There is no dispute about facts of Nature.

I dispute the degree to which these would operate in the system that was =
first described, when it was asked how the copper colour came to be on =
the outside of a jar or a vase that had a copper glaze on its interior =
surfaces and a plain glaze on its exterior.

I also proposed a possible explanation that has been ignored. I =
suggested that if the water in which the glaze was mixed had been =
slightly acidic and reacted with insoluble copper carbonate to form a =
soluble salt it could be transported through the porous clay to the =
outside glaze by capillary activity.

Best regards,

Ivor Lewis.
Redhill,
South Australia.

Ivor and Olive Lewis on tue 28 aug 07

Dear Bill Merrill=20

You may well be correct, but that does not explain why the copper =
compound migrated from the glaze inside of a pot to the outside, which =
was the original question.

Best regards,

Ivor Lewis.
Redhill,
South Australia.

WJ Seidl on wed 29 aug 07

Steve and Ivor:
Not necessarily.
In order for copper migration through a clay body to take place (begin),
there would have to be a catalyst. I'm thinking that heat differential
between the (cooler)
inside of the pot and the outside (which gets more heat more quickly)
would precipitate that
process, and start the migration on a molecular level perhaps.
Having the bottom sitting on a kiln shelf would negate the temperature
differential, thus, no migration
to the bottom.

Just a thought. I'm probably way out in left field on this one.

Personally, I'm putting copper migration through clay into the "I saw
Sasquatch at a picnic with Elvis" category
until someone can offer me proof. Not that I'm not fascinated by the
concept.

Here's another thought. In my industry, salts migration through fired
clay tile is well documented. It's a phenomenon
known as "efflorescence", and the catalyst is long-term exposure to water.
Could it be a copper SALT (as opposed to metal) migrating through, then
mixing with the fluxing outer layer of the
clay body or glaze to cause the flashing? This seems more likely.

Best,
Wayne Seidl

claystevslat wrote:
> Ivor --
>
> You're making this too complex. If copper travels through
> the bisqued body, every piece you have ever fired standing
> directly on a shelf with copper in the glaze is a test of
> your thesis.
>
> Why? Because standing 'hard' on a shelf will leave the
> bottom completely exposed to the "capillary action" you
> propose for diffusion through the clay but relatively
> protected from atmospheric movement, and the sides,
> exposed to atmosphere *and* your proposed capillary
> action stand as a control. (Checking the bottom also
> eliminates the possibility that 'spitting' through the
> open atmosphere is what causes the effect.)
>
> If the unglazed bottoms of your pots show signs of copper
> color, then it's arguable that diffusion through the clay
> takes place. If the copper shows up on the exterior sides
> (exposed to the open atmosphere of the kiln) but not on the
> bottom, transmission through the atmosphere is indicated.
>
> And, for what it's worth, some metal solids at room
> temperatures have detectable aromas. Melting is not
> required to make it work, it's sublimation from solid
> to gas that has the effect. You don't need to sniff molten
> iron to smell it, for example.
>
>
>
>
>
> --- In clayart@yahoogroups.com, Ivor and Olive Lewis
> wrote:
>
>> Dear Steve Slatin,
>>
>> If you wish to investigate the behaviour of Copper compounds via a
>>
> practical test you have to isolate the variable that you are
> monitoring from all other influences. This cannot be done in an
> active pottery kiln. There are ingredients in some glazes that
> decompose as they are heated and are prone to "Spitting". As I
> recall, one culprit is Gerstley Borate. So a spitting glaze could
> convey Copper oxide or Copper Carbonate into the breeze to settle on
> other surfaces. This effect can be eliminated by putting pure
> samples of Copper compounds on an inert carrier and placing these
> close to, say ten millimetres, but not in contact with a glaze
> sample,
>
>
> ______________________________________________________________________________
> 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.
>
>

claystevslat on wed 29 aug 07

Ivor --

You're making this too complex. If copper travels through
the bisqued body, every piece you have ever fired standing
directly on a shelf with copper in the glaze is a test of
your thesis.

Why? Because standing 'hard' on a shelf will leave the
bottom completely exposed to the "capillary action" you
propose for diffusion through the clay but relatively
protected from atmospheric movement, and the sides,
exposed to atmosphere *and* your proposed capillary
action stand as a control. (Checking the bottom also
eliminates the possibility that 'spitting' through the
open atmosphere is what causes the effect.)

If the unglazed bottoms of your pots show signs of copper
color, then it's arguable that diffusion through the clay
takes place. If the copper shows up on the exterior sides
(exposed to the open atmosphere of the kiln) but not on the
bottom, transmission through the atmosphere is indicated.

And, for what it's worth, some metal solids at room
temperatures have detectable aromas. Melting is not
required to make it work, it's sublimation from solid
to gas that has the effect. You don't need to sniff molten
iron to smell it, for example.





--- In clayart@yahoogroups.com, Ivor and Olive Lewis
wrote:
>
> Dear Steve Slatin,
>
> If you wish to investigate the behaviour of Copper compounds via a
practical test you have to isolate the variable that you are
monitoring from all other influences. This cannot be done in an
active pottery kiln. There are ingredients in some glazes that
decompose as they are heated and are prone to "Spitting". As I
recall, one culprit is Gerstley Borate. So a spitting glaze could
convey Copper oxide or Copper Carbonate into the breeze to settle on
other surfaces. This effect can be eliminated by putting pure
samples of Copper compounds on an inert carrier and placing these
close to, say ten millimetres, but not in contact with a glaze
sample,
>

Paul Haigh on fri 31 aug 07

Wayne-
Diffusion of any sort does not require a heat differential. If someone does it in an elevator, and you smell it- that's diffusion. Diffusion through membranes, capillary effect, likewise, do not work because of a temperature gradient.

I'm not proposing a mechanism, just stating that it absolutely is not driven by a temp gradient. It is driven by a concentration gradient, and the mechanism is just random molecular movement.

If someone thinks that copper is going THROUGH clay- then break it open and look for that red inside the fired piece.

Paul Haigh
Londonderry, NH

Ivor and Olive Lewis on sat 1 sep 07

Dear Wayne Seidl,
If readers would digest what was presented and answer or comment with =
precision, rather than responding in colloquial shorthand, this =
confusion about the behaviour of copper compounds would not arise.
I only suggested that it was possible for insoluble copper compounds to =
react with acid to form soluble salts and that these might migrate =
through the bisque clay.
Migration of salts from glaze slop into bisque clay does happen. I have =
a glaze that throws out a yellow discolouration at the outer surface =
after I have applied glaze to the interior of pots. I know not what it =
is and it has never concerned me.
Thanks for joining in.
Best regards,
Ivor Lewis.
Redhill,
South Australia.