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bronze, melting temps, pit firing

updated tue 30 apr 02

 

karen lovenguth on fri 26 apr 02


Hi all,
I have been following a bit the discussion
about patinas and bronze. My claywork is pit fired and
finally not very utilitarian. That is just its nature.
I have had some thoughts though about casting a few of
my pieces in bronze to be able to use as a pot for a
plant. Many of my pieces are inspired from plant
forms. I would love to be able to plant a certain
plant in a certain pot but as I said low temp pit
firing work doesn┤t like to get wet and finally will
not wear well to an outside climate. I was wondering
if I were to give a patina to a bronze piece,then
could I put it in a pit and get the effects of the
fire and smoke,oxidation and reduction? Or will it
just melt? Has anyone had any experience with that? My
husband has lots of bronze sculptures here but I don┤t
think it would be a good idea to try out my idea on
them!! Hope someone can help.Karen

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Snail Scott on sat 27 apr 02


At 01:13 PM 4/26/02 -0500, you wrote:
> When you patina bronze, you are applying a certain chemical or=
substance
>to the surface to bring about a reaction with the surface of the bronze=
that
>changes said surface. This is the "rusting" of the bronze. There are a wide
>array of materials and techniques available to bring about an equally wide
>array of results.=20


Let ne clarify some of this, since I was a professional=20
bronze patineur for a number of years.

SOME patinas are the result of a chemical interaction=20
with the metal. Among these are the co-called 'cold'=20
patinas, which include burial patinas, cold chemical=20
patinas, and fume patinas. No heat is necessary to=20
produce these effects, but heat will actually destroy=20
most of them. The classic burial patinas were originally=20
developed in the Renaissance to simulate the look of the=20
then-recently rediscovered Classical bronze sculpture,=20
and relies on creating an accelerated equivalent to=20
burial in those acidic Mediterranean soils. An easy and=20
common method is to moisten sawdust with vinegar and=20
put it in a trashbag with the bronze. Vivid teal greens=20
will begin to appear within days. Adding ammonia (either=20
from a bottle or piss) will create bluer colors. All=20
of these effects will be destroyed with just a few=20
hundred degrees of heat, though. Chemicals designed for=20
cold application are also vulnerable to heat, except=20
for a few, such as gun-blueing solutions for brass and=20
bronze.

Hot patinas are not really chemical reactions in the=20
same sense. Though some create a small amount of reaction=20
with the metal, most involve using a torch to heat the=20
metal to a temperature which fuses the chemicals onto the=20
surface, creating a durable 'crust' of color. It is not=20
a chemical reaction with the metal which causes this, but=20
the reaction of the chemical to the heat. Manipulation of=20
the amount of heat, duration of heat, intervals of heating,=20
concentration of chemicals, quantity of chemicals, and=20
method of application all will affect the final color of=20
the patina. So, while most hot patinas are not destroyed=20
outright by reheating, they will be irrevocable altered.
Some, such as the copper-green 'verdigris' colors, will=20
blacken and even peel off, while others will merely=20
darken.=20

By the way, that brown patina which was mentioned is NOT=20
an effect of 'rusting' the bronze. The ubiquity of that=20
particular patina leads many laypeople to assume that it=20
must be some natural result of bronze-casting processes,=20
but it is human-induced, by applying successive layers=20
of ferric nitrate to the heated bronze. It's a coating.

Some so-called patinas, especially those sold in hobby=20
and craft stores, are really just types of paint, and=20
will be altered by heat according to the base of the=20
paint and the identity of its colorants.

One may consider the oxidation colors produced by heating,=20
(or by leaving the piece to sit around) to be the natural=20
form of patina. However, these effects are microscopically=20
thin and not really durable. And, further heating will=20
cause the oxide layer to thicken and turn gray. And the=20
verdigris greens, which are the real 'bronze rust', are=20
very vulnerable to heat, as described above.

There is little danger of accidentally melting the bronze=20
in a pit fire, though, since the melting point of bronze=20
is around 1800=BAF. Since bronze is not porous clay,=20
however, there is not likely ot be any interesting smoke=20
effects from pit-firing the metal, either, though you may=20
induce some heat-related effects.

(Sorry I didn't respond earlier; I've been a bit busy.)

-Snail

Craig Clark on mon 29 apr 02


Snail has given the type of summary that only a professional is capable
of. I can't even pronounce patineur (I've checked the spelling twice to
write this.)
I did not know that the quesiton had to deal with the "brownish" type
surface that is often seen. THe result o, as Snail points out, of ferric
nitrate being applied in several layers to heated bronze.
My use of the word "rust" was not specific enough. I was using it in a
figurative, rather than literal, manner to convey the idea that a change
was occurring on the surface of the bronze that in many instances involves
differing degress of oxidation. My mistake for lacking specificity. Snail
set the record straight in a clear and conscise manner.
I've not been able to find the book that I was looking for. Can't even
remember the title. All I remember is that it was written by a man who had
done extensive testing of about a bazillian different methods of "coloring"
bronze through the process known as patina.
It was not a cheap book...nice coffe table size......great full color
pictures of all the numbered tile tests. Extremely well organized. It may
have been titled something like"The patination of Bronze, brass and orther
metals." though I'm not sure. There was even a section on the patination of
steel.
If you are interested contact me off the list and I'll do a search of
books in print and see what I can come up with. Alternatively, see if Snail
knows the title.
Craig Dunn Clark
619 East 11 1/2 st
Houston, Texas 77008
(713)861-2083
mudman@hal-pc.org

The point
----- Original Message -----
From: "Snail Scott"
To:
Sent: Saturday, April 27, 2002 11:24 AM
Subject: Re: bronze, melting temps, pit firing


At 01:13 PM 4/26/02 -0500, you wrote:
> When you patina bronze, you are applying a certain chemical or
substance
>to the surface to bring about a reaction with the surface of the bronze
that
>changes said surface. This is the "rusting" of the bronze. There are a wide
>array of materials and techniques available to bring about an equally wide
>array of results.


Let ne clarify some of this, since I was a professional
bronze patineur for a number of years.

SOME patinas are the result of a chemical interaction
with the metal. Among these are the co-called 'cold'
patinas, which include burial patinas, cold chemical
patinas, and fume patinas. No heat is necessary to
produce these effects, but heat will actually destroy
most of them. The classic burial patinas were originally
developed in the Renaissance to simulate the look of the
then-recently rediscovered Classical bronze sculpture,
and relies on creating an accelerated equivalent to
burial in those acidic Mediterranean soils. An easy and
common method is to moisten sawdust with vinegar and
put it in a trashbag with the bronze. Vivid teal greens
will begin to appear within days. Adding ammonia (either
from a bottle or piss) will create bluer colors. All
of these effects will be destroyed with just a few
hundred degrees of heat, though. Chemicals designed for
cold application are also vulnerable to heat, except
for a few, such as gun-blueing solutions for brass and
bronze.

Hot patinas are not really chemical reactions in the
same sense. Though some create a small amount of reaction
with the metal, most involve using a torch to heat the
metal to a temperature which fuses the chemicals onto the
surface, creating a durable 'crust' of color. It is not
a chemical reaction with the metal which causes this, but
the reaction of the chemical to the heat. Manipulation of
the amount of heat, duration of heat, intervals of heating,
concentration of chemicals, quantity of chemicals, and
method of application all will affect the final color of
the patina. So, while most hot patinas are not destroyed
outright by reheating, they will be irrevocable altered.
Some, such as the copper-green 'verdigris' colors, will
blacken and even peel off, while others will merely
darken.

By the way, that brown patina which was mentioned is NOT
an effect of 'rusting' the bronze. The ubiquity of that
particular patina leads many laypeople to assume that it
must be some natural result of bronze-casting processes,
but it is human-induced, by applying successive layers
of ferric nitrate to the heated bronze. It's a coating.

Some so-called patinas, especially those sold in hobby
and craft stores, are really just types of paint, and
will be altered by heat according to the base of the
paint and the identity of its colorants.

One may consider the oxidation colors produced by heating,
(or by leaving the piece to sit around) to be the natural
form of patina. However, these effects are microscopically
thin and not really durable. And, further heating will
cause the oxide layer to thicken and turn gray. And the
verdigris greens, which are the real 'bronze rust', are
very vulnerable to heat, as described above.

There is little danger of accidentally melting the bronze
in a pit fire, though, since the melting point of bronze
is around 1800║F. Since bronze is not porous clay,
however, there is not likely ot be any interesting smoke
effects from pit-firing the metal, either, though you may
induce some heat-related effects.

(Sorry I didn't respond earlier; I've been a bit busy.)

-Snail

____________________________________________________________________________
__
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.

Michele Jurist on mon 29 apr 02


The book I think you are thinking of is, The Coloring, Bronzing and
Patination of Metals, by Richard Hughes, Michael Rowe. Amazon should have
it.
Michele
----- Original Message -----
From: "Craig Clark"
To:
Sent: Monday, April 29, 2002 8:10 AM
Subject: Re: bronze, melting temps, pit firing


> Snail has given the type of summary that only a professional is
capable
> of. I can't even pronounce patineur (I've checked the spelling twice to
> write this.)
> I did not know that the quesiton had to deal with the "brownish" type
> surface that is often seen. THe result o, as Snail points out, of ferric
> nitrate being applied in several layers to heated bronze.
> My use of the word "rust" was not specific enough. I was using it in a
> figurative, rather than literal, manner to convey the idea that a change
> was occurring on the surface of the bronze that in many instances involves
> differing degress of oxidation. My mistake for lacking specificity. Snail
> set the record straight in a clear and conscise manner.
> I've not been able to find the book that I was looking for. Can't even
> remember the title. All I remember is that it was written by a man who had
> done extensive testing of about a bazillian different methods of
"coloring"
> bronze through the process known as patina.
> It was not a cheap book...nice coffe table size......great full color
> pictures of all the numbered tile tests. Extremely well organized. It may
> have been titled something like"The patination of Bronze, brass and orther
> metals." though I'm not sure. There was even a section on the patination
of
> steel.
> If you are interested contact me off the list and I'll do a search of
> books in print and see what I can come up with. Alternatively, see if
Snail
> knows the title.
> Craig Dunn Clark
> 619 East 11 1/2 st
> Houston, Texas 77008
> (713)861-2083
> mudman@hal-pc.org
>
> The point
> ----- Original Message -----
> From: "Snail Scott"
> To:
> Sent: Saturday, April 27, 2002 11:24 AM
> Subject: Re: bronze, melting temps, pit firing
>
>
> At 01:13 PM 4/26/02 -0500, you wrote:
> > When you patina bronze, you are applying a certain chemical or
> substance
> >to the surface to bring about a reaction with the surface of the bronze
> that
> >changes said surface. This is the "rusting" of the bronze. There are a
wide
> >array of materials and techniques available to bring about an equally
wide
> >array of results.
>
>
> Let ne clarify some of this, since I was a professional
> bronze patineur for a number of years.
>
> SOME patinas are the result of a chemical interaction
> with the metal. Among these are the co-called 'cold'
> patinas, which include burial patinas, cold chemical
> patinas, and fume patinas. No heat is necessary to
> produce these effects, but heat will actually destroy
> most of them. The classic burial patinas were originally
> developed in the Renaissance to simulate the look of the
> then-recently rediscovered Classical bronze sculpture,
> and relies on creating an accelerated equivalent to
> burial in those acidic Mediterranean soils. An easy and
> common method is to moisten sawdust with vinegar and
> put it in a trashbag with the bronze. Vivid teal greens
> will begin to appear within days. Adding ammonia (either
> from a bottle or piss) will create bluer colors. All
> of these effects will be destroyed with just a few
> hundred degrees of heat, though. Chemicals designed for
> cold application are also vulnerable to heat, except
> for a few, such as gun-blueing solutions for brass and
> bronze.
>
> Hot patinas are not really chemical reactions in the
> same sense. Though some create a small amount of reaction
> with the metal, most involve using a torch to heat the
> metal to a temperature which fuses the chemicals onto the
> surface, creating a durable 'crust' of color. It is not
> a chemical reaction with the metal which causes this, but
> the reaction of the chemical to the heat. Manipulation of
> the amount of heat, duration of heat, intervals of heating,
> concentration of chemicals, quantity of chemicals, and
> method of application all will affect the final color of
> the patina. So, while most hot patinas are not destroyed
> outright by reheating, they will be irrevocable altered.
> Some, such as the copper-green 'verdigris' colors, will
> blacken and even peel off, while others will merely
> darken.
>
> By the way, that brown patina which was mentioned is NOT
> an effect of 'rusting' the bronze. The ubiquity of that
> particular patina leads many laypeople to assume that it
> must be some natural result of bronze-casting processes,
> but it is human-induced, by applying successive layers
> of ferric nitrate to the heated bronze. It's a coating.
>
> Some so-called patinas, especially those sold in hobby
> and craft stores, are really just types of paint, and
> will be altered by heat according to the base of the
> paint and the identity of its colorants.
>
> One may consider the oxidation colors produced by heating,
> (or by leaving the piece to sit around) to be the natural
> form of patina. However, these effects are microscopically
> thin and not really durable. And, further heating will
> cause the oxide layer to thicken and turn gray. And the
> verdigris greens, which are the real 'bronze rust', are
> very vulnerable to heat, as described above.
>
> There is little danger of accidentally melting the bronze
> in a pit fire, though, since the melting point of bronze
> is around 1800║F. Since bronze is not porous clay,
> however, there is not likely ot be any interesting smoke
> effects from pit-firing the metal, either, though you may
> induce some heat-related effects.
>
> (Sorry I didn't respond earlier; I've been a bit busy.)
>
> -Snail
>
>
____________________________________________________________________________
> __
> 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.
>
>
____________________________________________________________________________
__
> 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.
>