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copper reds once aga

updated fri 15 aug 08

 

Ivor and Olive Lewis on mon 11 aug 08


Dear Jean Szostek ,
I know of no reason why Tin oxide should be added to a glaze other
than to make an opaque white surface. Why it should be used as an
ingredient in a reduced Copper glaze seems to have no technical
reason.
However, speculating, Tin is extracted from its ores by reducing
strongly to get the metal. If this happened in a Glaze then the metal
would be distributed freely through the melt and might combine with
Copper metal to become a bronze alloy. In this way it may stabilise
the colour, or move its hue towards the orange range of the spectrum.
Best regards,
Ivor Lewis.
Redhill,
South Australia.

Neon-Cat on tue 12 aug 08


Dear Ivor and all,

Ivor, why do you only ever consider metal as a result of a metal oxide being
included (or coming into a glaze mix as a contaminant) in the glaze melt? If
we begin with tin as Sn (crystalline solid), SnO (crystalline solid - oxide)
or SnO2 (the crystalline solid oxide we potters use) we may well end up with
SnSiO3 (a glassy solid). Why do you not also consider this amorphous
semi-metal oxide (SnSiO3)? or maybe even SnSi2O5 and SnSi2O6, for example?
After all we are working heavily with silica as our glass forming
constituent of a glaze and it's going to combine with elements while forming
our glaze. To take a stand that we will only "see" native elements within a
glaze is rather misleading and shortsighted. The crystallization and
decomposition of tin oxide-silicon glasses, SnO-SiO2, including SnSiO3 glass
and the others, is well known and reported in the literature. With these
compounds or other similar compounds, as the dissolved oxygen within the
glaze continually varies the compounds are not particularly limited and may
be single valency or mixed valency within a silicate chain. These types of
chains serve to link and knit our glazes together. The metal ions are then
irregularly scattered among the attached silicates. Adding tin to a copper
glaze, as is common, probably enhances the reflection and refraction of
light and thus the color we preceive. We are surely not going to form bronze
by "smelting" tin and copper in our glazes. Within the context of our glazes
the small percentages of copper and tin involved are probably not going to
find one another and combine to form metals, either as tin and copper
separately or as a mix of tin-copper, as in bronze. They are loving the one
they're with - the silicates. Thus bound by structural mechanisms they can't
get away. I like a touch of strange once in awhile, but to try to imagine
we're creating bronze in our glazes in typical pottery kilns, no matter how
entergectically they're firing, is altogether too strange.

If you cover your pot with excess oxides or ores, yes you can get some metal
deposition on and around the glaze or on a pot body under certain kiln
conditions. I am doing this with hematite:
2Fe2O3 + 3C ---> 4Fe + 3CO2
Some of the iron in this case is also combining with the silicates to become
part of the glaze's colorful silicate structure.

Handy factoids:

Silicon oxidation state: Si 4+

Three common silica anions:
SiO4 4- orthosilicate
Si2O7 6- pyrosilicate
SiO3 2- (SiO3 2-)n chain

Oxidation states for tin:

Sn+2 Tin II or Stannous
Sn+4 Tin IV or Stannic

Orthosilicate examples:
Sodium Silicate -- Na4SiO4
Zircon -- ZrSiO4
Olivine - (Mg, Fe)2SiO4

Pyrosilicate (mineral) examples:
Kristiansenite -- Ca2ScSn(Si2O7)(Si2O6OH)
Hemimorphite -- Zn4Si2O7[OH]2.H2O
Lawsonite -- CaAl2Si2O7[OH]2.H2O

Examples (minerals) of silicate chains:
Augite -- (Ca,Mg,Fe)SiO3
Wollastonite -- CaSiO3
Rhodonite -- (Mn,Fe,Mg,Ca)SiO3

Marian
www.neon-cat.com


-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG]On Behalf Of Ivor and Olive
Lewis
Sent: Monday, August 11, 2008 2:37 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: copper reds once aga

Dear Jean Szostek ,
I know of no reason why Tin oxide should be added to a glaze other
than to make an opaque white surface. Why it should be used as an
ingredient in a reduced Copper glaze seems to have no technical
reason.
However, speculating, Tin is extracted from its ores by reducing
strongly to get the metal. If this happened in a Glaze then the metal
would be distributed freely through the melt and might combine with
Copper metal to become a bronze alloy. In this way it may stabilise
the colour, or move its hue towards the orange range of the spectrum.
Best regards,
Ivor Lewis.
Redhill,
South Australia.

jean szostek on tue 12 aug 08


hi ivor and hi marian,
first of all im not a chemist like you two, but about de discussion on tin
(that was a question of wyndham) i only can talk about my experiences
and they tells me that tin changes the color of my recipe and it is like you
say ivor, that the red becomes more orange, and i dislike it.
so i have to continue without tin.
the only difficulty with my glaze was that it is very fluid, meanwhile i
found a solution.
anyway thank you very mutch for all the explainations, from the two of you
il hope i still can learn mutch in the future from many clayarters
greatings jean
----- Original Message -----
From: "Ivor and Olive Lewis"
To:
Sent: Monday, August 11, 2008 9:36 AM
Subject: copper reds once aga


> Dear Jean Szostek ,
> I know of no reason why Tin oxide should be added to a glaze other
> than to make an opaque white surface. Why it should be used as an
> ingredient in a reduced Copper glaze seems to have no technical
> reason.
> However, speculating, Tin is extracted from its ores by reducing
> strongly to get the metal. If this happened in a Glaze then the metal
> would be distributed freely through the melt and might combine with
> Copper metal to become a bronze alloy. In this way it may stabilise
> the colour, or move its hue towards the orange range of the spectrum.
> Best regards,
> Ivor Lewis.
> Redhill,
> South Australia.
>
> No virus found in this incoming message.
> Checked by AVG - http://www.avg.com
> Version: 8.0.138 / Virus Database: 270.6.1/1605 - Release Date: 11/08/2008
> 16:59
>
>
>

jonathan byler on tue 12 aug 08


jean,

would you be willing to share what you did to make the glaze less
fluid? How is this effecting the color and texture of your work?

when I get some other projects wrapped up, I want to do some more
experiments with copper reds. some people hate them, but I am a
sucker for bright red, especially reduction fired copper reds.

thanks,

jon


jon byler
3-D Building Coordinator
Art Department
Auburn University, AL 36849

On Aug 12, 2008, at 2:43 PM, jean szostek wrote:

> hi ivor and hi marian,
> first of all im not a chemist like you two, but about de discussion
> on tin
> (that was a question of wyndham) i only can talk about my experiences
> and they tells me that tin changes the color of my recipe and it is
> like you
> say ivor, that the red becomes more orange, and i dislike it.
> so i have to continue without tin.
> the only difficulty with my glaze was that it is very fluid,
> meanwhile i
> found a solution.
> anyway thank you very mutch for all the explainations, from the two
> of you
> il hope i still can learn mutch in the future from many clayarters
> greatings jean
> ----- Original Message -----
> From: "Ivor and Olive Lewis"
> To:
> Sent: Monday, August 11, 2008 9:36 AM
> Subject: copper reds once aga
>
>
>> Dear Jean Szostek ,
>> I know of no reason why Tin oxide should be added to a glaze other
>> than to make an opaque white surface. Why it should be used as an
>> ingredient in a reduced Copper glaze seems to have no technical
>> reason.
>> However, speculating, Tin is extracted from its ores by reducing
>> strongly to get the metal. If this happened in a Glaze then the
>> metal
>> would be distributed freely through the melt and might combine with
>> Copper metal to become a bronze alloy. In this way it may stabilise
>> the colour, or move its hue towards the orange range of the spectrum.
>> Best regards,
>> Ivor Lewis.
>> Redhill,
>> South Australia.
>>
>> No virus found in this incoming message.
>> Checked by AVG - http://www.avg.com
>> Version: 8.0.138 / Virus Database: 270.6.1/1605 - Release Date:
>> 11/08/2008
>> 16:59
>>
>>
>>

jean szostek on wed 13 aug 08


hi jon,
naturally i will share how to do it, under my copper red i spray a very tin
layer ofthe following recipe
Potash Feldspar 28,5
Magnesium carbon. 2,2
Whiting 15,6 over the glaze
Kaolin 16,2
Quartz 33,5
---------
100

Cornish Stone 50
Whiting 20 under the glaze
Quartz 25
Kaolin 15
the glaze that i spray over my copper red, makes it a little bit darker, im
trying out now if im adding tin to the upper layer if the color stay, but i
dont think so
mutch pleasure jon
the people that hate copper red have not the caracter to continue
in the beginning it was for me a hate/love relation, buth it bit me so bat
that it become maniacle
i had now help from anyone here in our little country, the potters here dont
give mutch of their "secrets"
but im glad about the results i achieved until now
hope for you on good results jon greatings jean
----- Original Message -----
From: "jonathan byler"
To:
Sent: Wednesday, August 13, 2008 2:28 AM
Subject: Re: copper reds once aga


> jean,
>
> would you be willing to share what you did to make the glaze less
> fluid? How is this effecting the color and texture of your work?
>
> when I get some other projects wrapped up, I want to do some more
> experiments with copper reds. some people hate them, but I am a
> sucker for bright red, especially reduction fired copper reds.
>
> thanks,
>
> jon
>
>
> jon byler
> 3-D Building Coordinator
> Art Department
> Auburn University, AL 36849
>
> On Aug 12, 2008, at 2:43 PM, jean szostek wrote:
>
>> hi ivor and hi marian,
>> first of all im not a chemist like you two, but about de discussion
>> on tin
>> (that was a question of wyndham) i only can talk about my experiences
>> and they tells me that tin changes the color of my recipe and it is
>> like you
>> say ivor, that the red becomes more orange, and i dislike it.
>> so i have to continue without tin.
>> the only difficulty with my glaze was that it is very fluid,
>> meanwhile i
>> found a solution.
>> anyway thank you very mutch for all the explainations, from the two
>> of you
>> il hope i still can learn mutch in the future from many clayarters
>> greatings jean
>> ----- Original Message -----
>> From: "Ivor and Olive Lewis"
>> To:
>> Sent: Monday, August 11, 2008 9:36 AM
>> Subject: copper reds once aga
>>
>>
>>> Dear Jean Szostek ,
>>> I know of no reason why Tin oxide should be added to a glaze other
>>> than to make an opaque white surface. Why it should be used as an
>>> ingredient in a reduced Copper glaze seems to have no technical
>>> reason.
>>> However, speculating, Tin is extracted from its ores by reducing
>>> strongly to get the metal. If this happened in a Glaze then the
>>> metal
>>> would be distributed freely through the melt and might combine with
>>> Copper metal to become a bronze alloy. In this way it may stabilise
>>> the colour, or move its hue towards the orange range of the spectrum.
>>> Best regards,
>>> Ivor Lewis.
>>> Redhill,
>>> South Australia.
>>>
>>> No virus found in this incoming message.
>>> Checked by AVG - http://www.avg.com
>>> Version: 8.0.138 / Virus Database: 270.6.1/1605 - Release Date:
>>> 11/08/2008
>>> 16:59
>>>
>>>
>>>
>
> No virus found in this incoming message.
> Checked by AVG - http://www.avg.com Version: 8.0.138 / Virus Database:
> 270.6.1/1608 - Release Date: 12/08/2008 16:59
>
>
>

Ivor and Olive Lewis on wed 13 aug 08


Dear Marian,
Perhaps you would have done better to address the questions posed by
Jean Szostek yourself instead of criticising my response.
You ask, "Ivor, why do you only ever consider metal as a result of a
metal oxide being included (or coming into a glaze mix as a
contaminant) in the glaze melt?" Not true. If you had followed my
argument rather than your own agenda you would realise that I have
pursued the notion of the formation of Metallic Silicates.
Regrettably I do not have a copy of the full series of Phase diagrams
as published on disc by ACerS. I have to make do with the 1979
reprint. Perhaps you are fortunate to have access to a larger library
in the USA.

Ivor Lewis.
Redhill,
South Australia.

Neon-Cat on thu 14 aug 08


Ivor and all, let's cut to the chase for a minute.

The color of a glaze is determined by the wavelength of the light
(electromagnetic radiation) that bounces off the substances in a glaze. When
we have ordinary visible (white) light of all wavelengths shining on a
glazed pot, the substances composing the glaze will reflect light at certain
wavelengths, absorb light at different wavelengths, and transmit light at
other wavelengths. Within a certain range of wavelengths the reflected and
transmitted wavelengths combine to produce the resulting color we see.
Copper absorbs blue, green and yellow light and reflects it away so we are
left seeing red. Whether light energy is absorbed depends on the structure
of the copper-containing substance and on the wavelength of the light. The
color we see is provided by light that was present in the original white
light that has not been removed by absorption by the fired glaze
ingredients. If two substances are influencing color then the colors of
light absorbed by each will be removed from the reflected light and we see
what is left. Over the years potters have discovered certain percentages of
materials and creative combinations of glaze materials that work best for
them in creating a copper red glaze.

In studies involving azurite and malachite, minerals often used in ancient
glazes, it was shown that these hydroxy-copper carbonates, as intact
entities, were not responsible for glaze color. It was demonstrated that
both azurite and malachite thermally decompose in six overlapping stages
from 250 - 8420 C (482 - 15480 F). The first two stages are associated with
the loss of water; stages three and four result from the simultaneous loss
of water and carbon dioxide. The sixth stage is associated with reduction of
cupric oxide to cuprous oxide and finally to copper. Thermal decomposition
is complete by 3750 C (7070 F).

The formation of Cupric oxide (CuO) colloidal particles occurs during
oxidation (or neutral firing). It might be assumed that cupric oxide can
then be reduced to cuprous oxide and copper in situ. Copper colloidal
particles are produced when firing in a reduction (CO) atmosphere. In
either case, the resulting copper is found in the Cu2+ state in interstitial
positions and substituting within the silica (SiO2) matrix. Changes in the
composition and size of the colloidal particles created influences the color
we see.

The type of light (incandescent, fluorescent, daylight, mixed lighting, etc)
shining on our pot will subtly affect its color. No matter the light source,
there will be interference patterns generated in the glaze by its different
constituents that affect the color we see. Light penetrates into the glaze
and is absorbed at different depths. There will also be places where a
copper atom, ion, oxide, or molecular complex will not be engaged by
electromagnetic radiation, such as in the interstitial clay layers or if it
is hidden behind another substance or cloistered within part of a silica
lattice so that there are blank (color) spots in the glaze where light is
neither absorbed nor emitted.

Other variables come in to play, too, like our clay bodies. In a glaze
copper will tend to accumulate at the outer surface or next to the clay
body. Glaze at the interface of the clay body will not only change the
nature of the clay but be altered itself as ions adsorb onto and into the
clay and the clay lattice is decomposed. As temperature increases we will
lose entirely the original structure of the clay as interstitial layers
become compressed or obliterated entirely. Each clay type of clay
(kaolinite, illite, smectite, etc.) differs from its buddies in how it will
react to a glaze, some strikingly so. The pH of a glaze, the metal oxides it
contains (many of which can be destructive to the clay body), the choice of
flux, etc., will affect the clay-glaze interface and thus glaze color. Glaze
surfaces will be most affected by changing kiln environments (oxidation,
reduction, neutral kiln conditions) and will react slightly differently than
a glaze interior. Of course there are many more variables affecting the
color of a glaze. I am most curious about what we might be creating through
chemical reactions in our glaze buckets even before a glaze goes on a pot
and how stable a particular glaze might be over days, weeks, and months.
But in the end, whatever we're creating in the kiln, what we see will be the
light emitted from a host of tiny electrons scattered within the glaze field
that are actually contacted by light and then emit light. Happy the potter
who has hit upon just the winning combination of ingredients to make those
copper red, red hot glazes.

If I could not check facts against current trends and findings in chemistry
before posting I'd feel at a severe disadvantage and most likely give up.
Phase diagrams are often updated as technology and testing methods advance.
For example in 1989, in a paper published by the American Ceramic Society,
the researchers point out that their binary Cu-Sn phase diagrams are in
conflict with published binary phase diagrams. They weren't the only ones
noticing differences. Here from a reliable source, the US National Institute
of Standards and Technology, is a more modern phase diagram for the
copper-tin system:
http://www.metallurgy.nist.gov/phase/solder/cusn-w.jpg
(http://www.metallurgy.nist.gov/phase/solder/cusn.html)

In one research paper from 2002, it was reported that tin oxide shows main
electromagnetic emission bands centered at about 480 nm and 630 nm that
correspond with visible green and red color. The intensity of both bands
increases up to 1200 C (21920 F) but both are totally quenched at 1500 C
(27320 F). Tin oxide melts between 1500 - 16300 C (2732 - 29660 F) and
sublimes between 1800 - 19000 C (3272 - 34520 F). Under some conditions it
can produce a cream color in glazes. What exactly it is doing, raw or fired,
in a copper red glaze and how is a story for another day. We now know it can
enhance red color. Hopefully further tin oxide details will follow as posted
by someone other than me. I gotta get my hands back in clay:>)

I hope everyone has a great day!

Marian
www.neon-cat.com


-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG]On Behalf Of Ivor and Olive
Lewis
Sent: Wednesday, August 13, 2008 2:04 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: copper reds once aga

Dear Marian,
Perhaps you would have done better to address the questions posed by
Jean Szostek yourself instead of criticising my response.
You ask, "Ivor, why do you only ever consider metal as a result of a
metal oxide being included (or coming into a glaze mix as a
contaminant) in the glaze melt?" Not true. If you had followed my
argument rather than your own agenda you would realise that I have
pursued the notion of the formation of Metallic Silicates.
Regrettably I do not have a copy of the full series of Phase diagrams
as published on disc by ACerS. I have to make do with the 1979
reprint. Perhaps you are fortunate to have access to a larger library
in the USA.

Ivor Lewis.
Redhill,
South Australia.