Eric Suchman on fri 28 may 04
Can I take the 'Alfred Porcelain Body' that Mel mentioned and drop it to ^6
by substituting Neph. Sy. for the Feldspar?
if you want porcelain.. take 25 china clay, 25 feldspar, 25 silica,
and 25 ball clay. mix it...and bingo...porcelain. (that is the old alfred
body, and still works well.) 25 can be pounds, ounces, coffee cans
or handfuls. in other words, a quarter of each. how much you need
is up to you.
Thanks,
Eric in Oceanside
David Beumee on sat 29 may 04
Eric,
Any clay body with 25% ball clay is going to fit a definition of porcelain that I do not accept. That much ball clay will darken the fired result far beyond the white fired result that will give a clarity to glaze color that I associate with porcelain. But workability and plasticity may well be the important factor for you, so a white stoneware body might work well. A straight across substitution of neph sy for Custer or G-200 may cause problems if the body isn't used immediately. Neph sy is a sodium based spar and leaching can occur over time. Sodium based compounds are used to deflocculate slurry into casting slip, exactly the opposite of what you want in a throwing body. Deflocculated clay is flabby and impossible to throw.
Also, as Craig Martell has pointed out, always mix by weight, not by volume. Volumetric mixing will throw the percetages off because some materials are heavier or lighter than others.
I don't know which ocean you're close to, but if you're on the east coast you might consider Tom Turner's cone six porcelain, available from Standard Ceramic Supply in Pittsburgh under the name "#601 Turner's Best C/6 Porcelain."
David Beumee
Earth Alchemy Pottery
Lafayette, CO
> Can I take the 'Alfred Porcelain Body' that Mel mentioned and drop it to ^6
> by substituting Neph. Sy. for the Feldspar?
>
> if you want porcelain.. take 25 china clay, 25 feldspar, 25 silica,
> and 25 ball clay. mix it...and bingo...porcelain. (that is the old alfred
> body, and still works well.) 25 can be pounds, ounces, coffee cans
> or handfuls. in other words, a quarter of each. how much you need
> is up to you.
>
> Thanks,
> Eric in Oceanside
>
> ______________________________________________________________________________
> 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.
Ivor and Olive Lewis on sat 29 may 04
Dear Eric of Oceanside,
> Can I take the 'Alfred Porcelain Body' that Mel mentioned and drop
it to ^6 by substituting Neph. Sy. for the Feldspar?<
Yes you could try that.
But there is a good reason why the raw clay may not have the physical
qualities you might expect.
The plastic nature will change. Sodium ions leached from the Neph Sy
cause a degree of deflocculation. But if you are making casting slip
that could be an advantage.
Best regards,
Ivor Lewis. Redhill, South Australia
Potters Council Member
Lois Ruben Aronow on sun 30 may 04
> I don't know which ocean you're close to, but if you're on
> the east coast you might consider Tom Turner's cone six
> porcelain, available from Standard Ceramic Supply in
> Pittsburgh under the name "#601 Turner's Best C/6 Porcelain."
I am in the process of trying the ^6 Turner body for 2 reasons: I'm not
interested in translucency for my regular work, and because I'm looking for
the very whitest body available.
I have to say that the Turner body is VERY pricey. VERY. If you are going
to give it a go, do yourself a favor and also try out Standard's #551 Very
Plastic Porcelain. It is extremely white and strong, and what I have been
using thus far. I think a lot of people don't know about it. It also
offers a lovely glowing translucency.
I'm not trying to knock the Turner porcelain (which I have not fired and
glazed yet). I'm just trying to let people know there are excellent
alternatives available and you should try them all when looking for a new
clay body.
* * * * * * *
Lois Ruben Aronow
Modern Porcelain & Tableware-Updated for Spring 2004!
www.loisaronow.com
L. P. Skeen on mon 31 may 04
Aha! I was thinking just this morning that I needed to tell Clayart about
the sample of ^6 white clay (I don't know if it's porcelain, but it IS
porcelainous) I got at NCECA. It is Great Lakes Clay Co. "Star Bright"
#MCL345 and it is W H I T E at ^6. I have only used it to handbuild some
jewelry pieces yet; have not thrown it, but if white is what you're after,
it's way white, whiter than Bmix ever thought about.
L
----- Original Message -----
From: "Lois Ruben Aronow"
you might consider Tom Turner's cone six
> > porcelain, available from Standard Ceramic Supply in
> > Pittsburgh
mailtoandrew@FSMAIL.NET on mon 31 may 04
Hello Eric,
25% CC, 25% BC, 25% feldspar and 25% silica is pretty good start, though
Im not sure why its described as being Alfred Porcelain as it is simply a
generic composition.
As far a substituting the feldspar for nepheline syenite ...
Whilst many different types of feldspars are available, each with
different fluxing action, nepheline syenite, is usually a stronger flux.
Neph. syn is not a feldspar, it is an igneous rock that in appearance
resembles a medium grained granite.
I would not like to comment on whether Na ions are leached from neph. sy.
or the effect on rheology of the body but many successful throwing bodies
use it.
It is perhaps also noting that the type or grade of china clay, ball clay
and silica will also influence the firing. Generally an increase in the
alkali content, K2O, Na2O and CaO, leads to a more fluxy and hence less
refractory body.
Perhaps the best approach is simply to try it! A few small trials should
be all that is needed followed by recipe modifications, such as if its not
vitreous add more flux.
Also just because a body contains 25% ball clay does not preclude it from
being porcelain.
Best of luck,
Andrew
David Beumee on tue 1 jun 04
Andrew wrote,
> Also just because a body contains 25% ball clay does not preclude it from
> being porcelain.
Any clay body that contains 25% of even the whitest burning ball clay will have enough iron content to color the fired result to the point that glazes will not have the clarity of appearence that a porcelain body will give. That may not be important to many, particularly because ball clay adds so much plasticity and workability. As Tom Turner says, if you go for translucency, you give up throwing ability and strength; if you go for plasticity, you give up whiteness; if you go for strength, you give up translucency. There's always a trade off.
David Beumee
Earth Alchemy Pottery
Lafayette, CO
> Hello Eric,
>
> 25% CC, 25% BC, 25% feldspar and 25% silica is pretty good start, though
> Im not sure why its described as being Alfred Porcelain as it is simply a
> generic composition.
>
> As far a substituting the feldspar for nepheline syenite ...
>
> Whilst many different types of feldspars are available, each with
> different fluxing action, nepheline syenite, is usually a stronger flux.
> Neph. syn is not a feldspar, it is an igneous rock that in appearance
> resembles a medium grained granite.
>
> I would not like to comment on whether Na ions are leached from neph. sy.
> or the effect on rheology of the body but many successful throwing bodies
> use it.
>
> It is perhaps also noting that the type or grade of china clay, ball clay
> and silica will also influence the firing. Generally an increase in the
> alkali content, K2O, Na2O and CaO, leads to a more fluxy and hence less
> refractory body.
>
> Perhaps the best approach is simply to try it! A few small trials should
> be all that is needed followed by recipe modifications, such as if its not
> vitreous add more flux.
>
> Also just because a body contains 25% ball clay does not preclude it from
> being porcelain.
>
> Best of luck,
>
> Andrew
>
> ______________________________________________________________________________
> 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.
Ron Roy on wed 2 jun 04
Hi Eric,
In theory you are correct - using Neph Sy will bring it down to cone 6 but
there are several factors to consider.
How well the clay is mixed is one. If my hand the mixing will not be as
well as with a machine - even the type of machine makes a difference. The
there is the slip method which mixed the best.
Hand mixed will need more heat to melt properly for instance.
Most potters want the absorbency of a porcelain like body to be close to
none. You can use a mix of Neph Sy and spar to open a body like that for
instance.
It would be best to do the absorbency testing - if you are hand mixing the
sample you can count on an increase in melting if the body is then mixed by
machine - count on about a 1% decrease in the % absorbency - some times
more if super mixed.
How long you intend to fire, soak and slow cool (what your glazes need)
will affect absorbency as well
Watch the mesh size of the Neph Sy - generally 270 is the right size - if
you use a finer mesh you get more melting and more Sodium leaching - which
means more tendency to deflocc.
Epsom salts will stop the defloccing - dissolve in water and add 2 lb. per
1000 dry weight of materials - 0.2 per 100 lb. dry materials. Add it in as
the water is added to the dry materials.
Leave out the salts in any body with Neph Sy and you can expect
deflocculation sooner or later.
If you are slip casting - as Andrew said - the deflocculation from Neph Sy
is welcome in a slip casting body.
Let me know if you want to know how to do absorption tests.
RR
>Can I take the 'Alfred Porcelain Body' that Mel mentioned and drop it to ^6
>by substituting Neph. Sy. for the Feldspar?
>
>if you want porcelain.. take 25 china clay, 25 feldspar, 25 silica,
>and 25 ball clay. mix it...and bingo...porcelain. (that is the old alfred
>body, and still works well.) 25 can be pounds, ounces, coffee cans
>or handfuls. in other words, a quarter of each. how much you need
>is up to you.
>
>Thanks,
> Eric in Oceanside
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
mailtoandrew@FSMAIL.NET on wed 2 jun 04
Hello David,
In response to your post:
You stated
1) ... Any clay body that contains 25% of even the whitest burning ball
clay will have enough iron content to color the fired result to the point
that glazes will not have the clarity of appearance that a porcelain body
will give ...
However a definition of porcelain must be related to the body and not the
glaze applied to it.
2) ....for translucency, you give up throwing ability and strength ...
Translucent bodies that are produced by plastic making methods are widely
used. As for strength do you mean unfired or fired? If the latter vitreous
bodies are invariably stronger than those which are porous and to achieve
translucency porosity must be minimised.
3) .... if you go for strength, you give up translucency ... again what
type of strength.
What is the definition of porcelain?
Is it by the ball clay content? No ... you considered that 25% ball clay
was too great but I worked for seven years with two porcelain bodies
containing very nearly 25% ball clay followed by another six years with
two further bodies with 30% ball clay, and only 10% kaolin.
Is it by flux content ... This is too broad as porcelains have been made
with feldspars, nepheline syenites, glass at a wide range of percentage
additions dependent on the fluxing action and firing temperature used.
Is it by china clay content .... certainly I think most people would
consider that a porcelain composition would contain some kaolin.
Given the huge range of raw materials used for porcelain bodies using this
a basis for a definition is almost certainly doomed. A definition based on
the fired body is likely to be more successful. Also remember that
porcelain is a ceramic material, and until a body has been subjected to
heat treatment it is not a ceramic.
So .... porcelain is white? Well what is white? I am neither playing
semantics nor being deliberately awkward. Simply placing a range of white
articles next to each other, even different types of paper, will show that
white varies. Colour, and I know Im pushing things to consider white a
colour, can be measured and quantified, such as by the l,a,b system, but
this is perhaps inconvenient to incorporate into a definition. Also the
addition of staining oxides has been used by some to produce coloured
porcelain.
Is porcelain translucent? Yes if it is made in thin sections but what
happens if the same formulation is used to make an article say a couple of
inches think? After firing it certainly will not be translucent.
Is it vitreous? ... Yes, but what is vitreous? Interpretations vary, from
zero open porosity to a specified degree of water absorbency, and the
extent of the latter can vary depending on the test method used.
Summary .... as with many terms interpretation can vary, and in an attempt
to standardise The American Society for Testing and Materials, ASTM,
issued the document C242 =96 01, Standard Terminology of Ceramic Whitewares
and Related Products. In this porcelain is defined as .... a glazed or
unglazed vitreous ceramic whiteware made by the porcelain process, and
used for technical purposes, designating such products as electrical,
chemical, mechanical, structural, and thermal wares when they are vitreous.
No mention of raw materials, colour or translucency.
There is of course potential for debate, including is bone china
porcelain? An arguement that has ended up in court on at least one
occasion concerning different levels of import tariff ... and what makes a
body stoneware rather than porcelain, is it simply that a porcelain plate
can be sold at a higher price than one made from stoneware????
Regards,
Andrew
Ivor and Olive Lewis on thu 3 jun 04
Dear Andrew,
Could it be that personal descriptions of Porcelain are derived from
value judgements based on individual perceptions, cultural precedents
or fashionable stereotypes?
Would it also be true to say that if a ceramic is translucent, that
quality exists throughout the mass regardless of the thickness
involved?
What is the opinion in the latest version of Hamer and Hamer?
Best regards,
Ivor Lewis. Redhill, South Australia
Potters Council Member
David Beumee on thu 3 jun 04
Hi Andrew,
You wrote:
"However a definition of porcelain must be related to the body and not the
glaze applied to it."
Ivor's right. Descriptions of porcelain are derived from value judgements based on individual perceptions (and experience), as well as cultural precedents and fashionable stereotypes. From my experience and perception and for what I'm trying to accomplish, a definition of porcelain could never separate fired clay body and glaze. Even a 5% addition of the whitest burning ball clay adds enough iron to the body to change the clarity of my celedons.
>" Translucent bodies that are produced by plastic making methods are widely
> used. As for strength do you mean unfired or fired? If the latter vitreous
> bodies are invariably stronger than those which are porous and to achieve
> translucency porosity must be minimised."
I'm talking about fired strength of a body with 0% absorption at cone 10. I'm a potter so I'm looking for a body that throws well, and if I'm working on translucency I begin with a recipe that I know well. I change the ratio of kaolin to spar until I see the slump test begin to sag at cone 10. If I throw and trim pots thin and use a transparent or translucent glaze I get translucency, but it always means a loss of workability, warping in the firing unless the forms are supported exactly right, and fragility of the fired result.
3) .... "if you go for strength, you give up translucency ... again what
> type of strength."
I'm talking about fired strength. Small percentages of alumina can be added to porcelain recipes for added strength, but you lose translucency. See the recipe for Pete Pinnell's porcelain in my article in CM, January 1994.
"What is the definition of porcelain?"
See Ivor's answer above. If you've worked with 25 or 30% ball clay in your clay bodies for 13 years, that's great. I've worked with porcelain bodies that contain no ball clay for 25 years because of what I'm trying to accomplish in my work. I would love to be able to add ball clay to my recipes, but I've tested over 70 individual ball clays for plasticity, shrinkage, absorption, warping and cracking, texture, and yes, fired color, and I know that even the whitest burning ones darken my clay body.
"Is it by flux content ... This is too broad as porcelains have been made
> with feldspars, nepheline syenites, glass at a wide range of percentage
> additions dependent on the fluxing action and firing temperature used."
The ratio of flux content to clay is higher tan that used for stoneware bodies.
Please see page 45 of my article on stoneware and porcelain in Studio Potter, Dec. 2003, Vol. 32 No.1.
> "Is it by china clay content .... certainly I think most people would
> consider that a porcelain composition would contain some kaolin."
Yes my friend! Kaolin is most certainly the basis and major constituent of porcelain clay bodies.
" Also remember that
> porcelain is a ceramic material, and until a body has been subjected to
> heat treatment it is not a ceramic."
Yes I will try to remember that fact. Thankyou.
" So .... porcelain is white? Well what is white?
Good! Exactly the point I've been trying to make! Please see page 42 of the Studio Potter article, entitled "How white is white?" It's all relative according to your own experience and taste. Ivor is right on the money.
"> There is of course potential for debate, including is bone china
> porcelain?"
Tom Turner has recently weighed in on this one, Comment, pages 110 and 112, May 2004 CM. I disagree with his statement that bone china is low temperature porcelain. There is an interface between clay and glaze that happens above cone 9 with porcelain clay bodies formulated for 0% porosity at cone 10 that gives the body an important strength,if the glaze remains uncrazed, that does not happen at cone 1 for bone china or at cone 6.
Best Regards,
David Beumee
Earth Alchemy Pottery
Lafayette, CO
> Hello David,
>
> In response to your post:
>
> You stated
>
> 1) ... Any clay body that contains 25% of even the whitest burning ball
> clay will have enough iron content to color the fired result to the point
> that glazes will not have the clarity of appearance that a porcelain body
> will give ...
>
However a definition of porcelain must be related to the body and not the
glaze applied to it.
> 2) ....for translucency, you give up throwing ability and strength ...
>
> Translucent bodies that are produced by plastic making methods are widely
> used. As for strength do you mean unfired or fired? If the latter vitreous
> bodies are invariably stronger than those which are porous and to achieve
> translucency porosity must be minimised.
>
> 3) .... if you go for strength, you give up translucency ... again what
> type of strength.
>
>
>
3) .... if you go for strength, you give up translucency ... again what
> type of strength.
>
> Is it by flux content ... This is too broad as porcelains have been made
> with feldspars, nepheline syenites, glass at a wide range of percentage
> additions dependent on the fluxing action and firing temperature used.
>
> Is it by china clay content .... certainly I think most people would
> consider that a porcelain composition would contain some kaolin.
>
> Given the huge range of raw materials used for porcelain bodies using this
> a basis for a definition is almost certainly doomed. A definition based on
> the fired body is likely to be more successful. Also remember that
> porcelain is a ceramic material, and until a body has been subjected to
> heat treatment it is not a ceramic.
>
> So .... porcelain is white? Well what is white? I am neither playing
> semantics nor being deliberately awkward. Simply placing a range of white
> articles next to each other, even different types of paper, will show that
> white varies. Colour, and I know Im pushing things to consider white a
> colour, can be measured and quantified, such as by the l,a,b system, but
> this is perhaps inconvenient to incorporate into a definition. Also the
> addition of staining oxides has been used by some to produce coloured
> porcelain.
>
> Is porcelain translucent? Yes if it is made in thin sections but what
> happens if the same formulation is used to make an article say a couple of
> inches think? After firing it certainly will not be translucent.
>
> Is it vitreous? ... Yes, but what is vitreous? Interpretations vary, from
> zero open porosity to a specified degree of water absorbency, and the
> extent of the latter can vary depending on the test method used.
>
> Summary .... as with many terms interpretation can vary, and in an attempt
> to standardise The American Society for Testing and Materials, ASTM,
> issued the document C242 – 01, Standard Terminology of Ceramic Whitewares
> and Related Products. In this porcelain is defined as .... a glazed or
> unglazed vitreous ceramic whiteware made by the porcelain process, and
> used for technical purposes, designating such products as electrical,
> chemical, mechanical, structural, and thermal wares when they are vitreous.
>
> No mention of raw materials, colour or translucency.
>
> There is of course potential for debate, including is bone china
> porcelain? An arguement that has ended up in court on at least one
> occasion concerning different levels of import tariff ... and what makes a
> body stoneware rather than porcelain, is it simply that a porcelain plate
> can be sold at a higher price than one made from stoneware????
>
> Regards,
>
>
> Andrew
>
> ______________________________________________________________________________
> 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.
mailtoandrew@FSMAIL.NET on thu 3 jun 04
Hello Ivor,
I agree that different understandings of what porcelain is do exist, in
addition to your list of influencing factors could be added the market.
For example within the antiques trade porcelains can sometimes be
described as true or artificial, depending if the article is old Chinese
or European. Such classification is not recognised by those making it.
It is important to appreciate the differences between a definition and a
description. The former obviously having to be all encompassing, precise
and accurate (and the last two terms being a reminder of the subject of a
previous debate!)
The ASTM quotation was included to show that definitions do exist, and by
a widely recognised authority.
Certainly there is no reason why a material should be excluded from being
a porcelain solely due to it be formulated from 25% ball clay.
Porcelain is made that is white, shades of white and coloured, and some
are of thick enough section to prevent any transmission of light.
I cannt agree with your suggestion that translucency may exists regardless
thickness of section. Translucency is imperfect transparency, i.e. they
transmit some light but with enough scatter and diffusion to mean an
object placed behind can be seen only in silhouette. Increasing section
thickness will eventually lead to all light being scattered and diffused
so an image can not be detected. Because of this the various test for
translucency, such as BS 5416, specify a thickness of specimen.
Regards,
Andrew
Ivor and Olive Lewis on fri 4 jun 04
Dear Andrew,
Thank you for your message.
Perhaps people create definitions for convenience. Persistent and
widespread use of a particular definition leads to a Convention. Once
a convention is established then the population accessing that
definition will divide. There will be those who adopt it as Dogma,
those who reject the dogma and those who make alternative choices.
I am amused by people who choose to use a clay body called
"Porcelain", giving the impression that they are employing a
convention of "sonorous", "translucent", "vitrified" and "white" and
complete the picture by staining their work black and/or covering it
with a black glaze.
Please read again your criticism of my suggestion that, if thin
sections of such a clay are translucent the whole mass is translucent.
Interference due to internal reflection and refraction may give the
appearance of opacity but they do not prevent the motion of light into
the mass. Several simple experiments will invalidate any claim that
the centre portion of a thick mass of a translucent material is
opaque.
Diminution of the amount of light which passes directly through a
porcelain is due more to the presence of occluded air (enclosed
porosity) than to the incorporation of impurities. But I would concede
that impurities in clay will interact with a glaze at the interface
where mutual dissolution and crystal regrowth take place.
Best regards,
Ivor Lewis. Redhill, South Australia
Potters Council Member
mailtoandrew@FSMAIL.NET on fri 4 jun 04
Hello Ivor,
Translucency ... I think there has been a little misunderstanding. I was
not disputing that whatever quality allows a porcelain to be translucent
will exist for all specimen geometries. My earlier posted just noted that
above a certain thickness no light will pass through an other wise
translucent porcelain.
However what about porous bodies? Certainly these are not taken to be
translucent as pores are excellent opacifiers(and much cheaper than
zircon!) but a very thin section of an earthenware is translucent.
Therefore is the article translucent or the material? This is why test
methods specify a section thickness.
Regards,
Andrew
Ivor and Olive Lewis on sat 5 jun 04
Dear Andrew,
Perhaps the Article is opaque even though the Material is translucent.
One thing I have pointed out before is that there is potential for a
translucent material to reflect light back to the observer. So beside
surface reflectivity you may also in some cases get total internal
reflection of light, albeit in a highly dispersed form. This will add,
when it happens, to surface luminosity.
I am in no doubt you can explain to us the Science behind the optical
effects of porosity.
So, just to change the subject, where did you get your training in
Ceramic Science? Your discursive style has a flavour of "Oxford and
Cambridge". Are you a product of "Taggs Yard"
Enjoy your weekend.
Best regards,
Ivor Lewis. Redhill, South Australia
Potters Council Member
----- Original Message -----
From:
To:
Sent: Saturday, 5 June 2004 12:04
Subject: Re: ^6porcelain body
> Hello Ivor,
>
> Translucency ... I think there has been a little misunderstanding. I
was
> not disputing that whatever quality allows a porcelain to be
translucent
> will exist for all specimen geometries. My earlier posted just noted
that
> above a certain thickness no light will pass through an other wise
> translucent porcelain.
>
> However what about porous bodies? Certainly these are not taken to
be
> translucent as pores are excellent opacifiers(and much cheaper than
> zircon!) but a very thin section of an earthenware is translucent.
>
> Therefore is the article translucent or the material? This is why
test
> methods specify a section thickness.
>
> Regards,
>
> Andrew
>
>
______________________________________________________________________
________
> 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.
mailtoandrew@FSMAIL.NET on sat 5 jun 04
Hello Ivor,
Is the article or material translucent? Well consider two extremes:
... if a porcelain body of the type normally used for translucent articles
is made thick enough no light will pass through, yet a very thin section
of a porous body can allow some light through. Given, as you are
previously noted, the interaction of light and pores is the dominant
influence for translucency it is the density of pores in a given section
that is the critical factor.
My background? Well its a little more humble than the distinguished
environs of Oxbridge. Academically it was eight years studying Ceramic
Technology at North Staffordshire Polytechnic, now Staffs Uni. My
employment history has included a number of ceramic manufacturers as well
as producers of clays, clay bodies and non-plastics.
Regards,
Andrew
Ivor and Olive Lewis on sun 6 jun 04
Hey Andrew,
We can carry this to extremes. Light will pass through gold. Just make
it thin enough. As for your white porous body, in the extreme that
behaves as a transparent medium and discernible images, not shadows,
can be seen through it.
Alter your pathway to knowledge.
Consider Whiteness and Transparency to be two extreme cases of the
same phenomenon with Translucency somewhere in the middle. Where does
that thinking lead ?
Not only distribution density but size has its influence. Given that
the materials of vitreous porcelain have the potential to be as
transparent as glass or gem quality minerals it is occluded gases that
have the greatest influence in negating the phenomenon.
Good background to support those on Clayart who have not had such
advantages. But Keep it Simple my Friend.
Best regards,
Ivor Lewis. Redhill, South Australia
Potters Council Member
mailtoandrew@FSMAIL.NET on mon 7 jun 04
I wouldnt wish to comment on the transparency or translucency of thin
sheets of gold as I have not studied the material. However I have seen
transparency in very thin sections of earthenware, and it was translucent
and not transparent.
And in addition to pore size being of influence could be added the amount
of glass within the material, or perhaps more accurately the relative
proportion of glass, crystals and pores.
And just before a misunderstanding leads to offence could you elaborate on
your comment: Alter your pathway to knowledge
Regards,
Andrew
mailtoandrew@FSMAIL.NET on mon 7 jun 04
Hello David, Ivor and anyone else thats stayed with this post,
1) David said =93...from my experience and perception and for what I'm
trying to accomplish a definition of porcelain could never separate fired
clay body and glaze....
Thats fine as no one can argue with what he wishes to make or disagree
with his own aesthetic criteria. But as bodies and glazes are two distinct
types of materials a definition of one can not be included in the other.
Also where does you definition leave unglazed porcelain, such a bisque,
which has a very long tradition of manufacture?
2) The statement ... if you go for translucency, you give up throwing
ability and strength; if you go for plasticity, you give up whiteness; if
you go for strength, you give up translucency.
As a broad overview this I would not disagree, except perhaps the
suggestion of an inverse relationship between strength and translucency.
If both porous and vitreous bodies of identcial geometry are being
considered the vitreous body will invariably exhibit a higher fired
strength than the porous. Yet the interference of light within the porous
body is so much greater.
3) David mentions that.... =94I've tested over 70 individual ball clays ....=
I know that even the whitest burning ones darken my clay body.=94
Raw materials are selected based on ones own acceptance criteria, however
others will have different requirements which may not be the same as
yours, and vice versa.
4) Flux content? I would agree the ratio of flux to clay is higher in
porcelains than stoneware. And I think this may be a useful guide to help
appreciate the difference. But it also leads into what is meant by
stoneware ... and my personal take it would include that historically they
were composed from a single clay relatively unbeneficiated, perhaps even
locally dug, clay. Stoneware clays are plastic, impure, secondary clays
that are vitreous after firing to around 1200=B0C without the inclusion of
additional fluxing minerals. Distinguishing between fire clay or stoneware
clays is vague and is largely by application. Current commercial stoneware
bodies, mock stoneware?, are composed from high amounts of secondary clays
with, sometimes, additional fluxes and fillers.
5) Whilst I stated earlier that most people would consider that a
porcelain composition would contain some kaolin David felt it was the
major constituent. Whilst it may well be of in his formulation, and even
many, but not all.
Ive worked with, as have others, porcelains with a kaolin composition down
to 10% and whilst certainly not of the whitest after firing this was not
an overriding concern.
Also where does a definition based on a high kaolin composition leave the
porcelains based on halloysite? I would not wish to suggest the opinion of
others but passed an article made from such a body and observed the high
whiteness and translucency there surely would be no argument about them
being porcelain.
6) What is white? I could not comment on the article referenced by David
as Ive not read it but I assume it discusses and elaborates on what may
initially seem to be obvious. A common example is when we come to re-
decorate and paint a new coat of white on an old surface.
I posed this question because if a definition of porcelain includes
whiteness then a definition of that term, or at least an understanding of
it, must be acknowledged. Also there are porcelain bodies that are being
produced that are distinct shades of white, or even some that one could
argue are not a shade of white but a very pale blue or grey, without the
use of added colouring compounds. And purposely coloured porcelains also
do exist.
Yes perception, semantics, experience ... many factors come in to play.
6) David is unhappy with the suggestion of bone china being described as
low temperature porcelain. I would agree with him though I have difficulty
in explaining why. Certainly BC exhibits most, probably all, the criteria
nearly all of us would ascribe to porcelain.
Firing temperature? A German ceramicist I know would only consider an
article to be made of porcelain if it had been reduction fired to low
biscuit followed by high glost. Would everyone agree? No .... however this
would certainly would exclude the majority of bone china, which is largely
high biscuit and low glost. But what about porcelains without bone ash
that have a similar schedule? And then porcelains that some once fire?
7) Almost everyone would agree porcelains are vitreous but what does this
term mean?
Saying 0% porosity is not sufficient as there are different types of
porosity, specifically open and closed. Nearly all whiteware bodies will
have some pores within the microstructure.
It is erroneous to think that all vitreous bodies are impermeable as many
do not have zero open porosity, even those which give a 0% water
absorption. And results of zero are rare due to very small amounts of
water that can remain on the surface.
There are agreed standards for what constitutes vitreous which includes
test procedures and the interpretation of results.
8) Some, not on this recent thread, have claimed its only porcelain if
Grolleg is used. Yet this is just a single grade of English kaolin. White
firing yes but there are others.
9) Another perspective ... I have a small blue and white dish purchased
from a reputable dealer which was described as Chinese porcelain circa
1600AD. Simple visual examination of unglazed areas shows buff to red
colour with the occasional with large aggregate inclusions, almost if made
from a crude, brick type clay. Certainly not porcelain, but as people
always think of the ancient Chinese having made porcelain ....
10) On a different, but related, thread Kat in the Hat wondered why
porcelains are perceived to be of such value. My personal view is that it
has much to do with the history, as commented on by Dave Finkelnburg, in
his reply to Kat.
Apparently the demand in Europe for porcelain when it first arrived was so
great that it cost, weight for weight, more than gold, and was even
thought initially to be a caved stone. It was owned, and extravagantly
displayed, only by the monarchies. Early work to replicate the material
was associated with alchemists and the search for the elixir of life.
The story of the early Europeans to make porcelain, Bottcher is believed
to be the first, is fascinating. Much information is available but link I
quickly found is http://www.oldandsold.com/articles04/pottery21.shtml
Having said that stoneware can be prestigious. Denby, based in England,
use make a stoneware body from a high percentage of locally dug fireclays
to produce some very attractive tableware.
So .... as I stated in my very first post to this thread 25% CC, 25% BC,
25% feldspar and 25% silica is pretty good start for a porcelain body; it
is a simple generic recipe that can be modified to particular
requirements, for example
If you want it more reactive, say vitreous at lower temp. add more flux.
If you want it whiter lower the ball clay content ... and on ....
Though dont forget each raw material makes a contribution to the final
properties.... some feldspars are high in Fe2O3 and TiO2, so are some
kaolins and silicas, some kaolins are quite fluxy, some ball clays contain
a lot of free silica ..... and on .... and on
Yes we have our own preferences but establishing definitions is difficult.
Ones do exist for porcelain, some of which do not mention whiteness or
translucency. Consider that the most widely accepted definition of a
ceramic as it doesnt refer to clay. How many potters are happy to accept
that?
Theres strong arguments on all sides, perhaps its a bit like the old adage
Is the glass half full or half empty, and we could almost be heading
towards philosophy.
I apologies if anyone is still reading this who thinks its all a little
pointless. Debate can be useful and interesting, and hopefully some of
this can help understand the background to the material and terms so
frequently used.
Regards,
Andrew
Ivor and Olive Lewis on tue 8 jun 04
Dear Andrew,
I thought I lifted that from 'Metals in the Service of Man but I seem
to be incorrect in my assumption of the source. However, that author
does tell us that one Grain Troy can be beaten out into a sheet 6 sq
ft in area or drawn into a wire 11/2 miles long. It is well know that
if you apply gold lustre thinly it does not form a lustrous metallic
film, but gives a ruby stain.
"Alter your pathway to knowledge" = "Search for what is not obvious"
or "What is being ignored ?"
It seems to me that Translucency and Whiteness are in opposition as
qualities, that if there is a high degree of one there will be low
degree of the other. I also feel that the attainment of either depends
on the physical attributes of the materials which contribute to the
fabric of the ceramic substance, and I include the gas in the
porosity as being one of these constituents. The way they behave in
concert toward light as well as our viewpoint with respect to the
pathway of light changes our perception.
Best regards,
Ivor Lewis. Redhill, South Australia
Potters Council Member
______________________________________________________________________
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> Send postings to clayart@lsv.ceramics.org
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mailtoandrew@FSMAIL.NET on tue 8 jun 04
Dear Ivor,
My only experience of ultra thin gold, apart from on the spines of books,
is ruining a gold leaf electroscope but as my old physics master never
found out Ill say no more about it ....
Your statement =93the attainment of either depends on the physical
attributes of the materials which contribute to the fabric of the ceramic
substance=94 is surely true for all characteristics: i.e. properties of the=
whole are influenced by properties of its components.
Your belief that translucency and whiteness are opposing qualities .... Do
you mean that white results from the reflection of all wavelengths of
visible light and translucency requires some light not to be reflected?
By that statement followed by =93The way they behave in concert toward light=
as well as our viewpoint with respect to the pathway of light changes our
perception.=94 are you suggesting translucency and whiteness are mutually
exclusive?
Im still puzzled by your earlier statement "Alter your pathway to
knowledge". Your reply to my request for elaboration was a simply re-
wording of the same. The original post of this came in response to my
detailing of observations of translucency through porcelain and very thin
section of earthenware.
Regards,
Andrew
Craig Dunn Clark on wed 9 jun 04
Steve, it has been my understanding that the color that we see is a
result of the reflection or refraction of either all (white), none (black),
or poritions of (various colors) the visible light spectrum. In absence of
said bundle of photons there is no percieved color. I am specifically
referencing a percieved color to attempt to avoid the question of "...if a
tree falls in the forest and no one is there to witness it is there a
sound...".I'm not attempting to slice those hairs.
I has also been my understanding, and one that I have repeated often,
that it is the molecular structure as well as the quality of the surface of
what we are observing that determines what amount, and frequency, of the
visible light spectrum that is reflected or refracted.
Keeping this in mind I would suggest that it is indeed a reflection of
the full visible light package that gives us the color that we refer to as
white. In the case of the closet test I suspect that there was indeed a fair
amount of reflection going on within the confines of the closet itself,
unless perhaps you were wearing black clothing from head to toe with black
face paint and the walls of the closet were also black as well as everything
in it with the exception of the bowl. There would also have been the
neccessity of having a completely dark closet which would most probably
entail the construction of some type of light trap either at the entrance of
or surrounding the closet in which the experiment occured.
The light being generated by the flashlight when using a conventional
bulb is also not of the full spectrum variety. Atleast I don't think so.
This will inturn affect the color that is percieved.
I guess I'm attempting to make the point that the color is a function of the
object and it's interaction with the light that it encounters.
Craig Dunn Clark
619 East 11 1/2 st
Houston, Texas 77008
(713)861-2083
mudman@hal-pc.org
----- Original Message -----
From: "Steve Slatin"
To:
Sent: Wednesday, June 09, 2004 2:14 PM
Subject: Re: ^6porcelain body
> Ivor --
>
> As you know, I rarely question your science as I believe you
> have a better handle on most pottery-related things than I do.
>
> I will challenge your statement about whiteness, however.
> I believe whiteness (as a characteristic) exists without light
> coming from the direction of the observer.
>
> I took a white bowl (porcelain, clear glaze) into a closet
> with no windows and closed the door. With a highly
> directional flashlight (maglight, AA type with the tiny
> bulb and fairly well focused beam) at my feet, the bowl
> appeared white. I moved it to 90 degrees from me around
> the bowl, and stood it my original position. As far as the
> 'shadow' point on the bowl, it still appeared extremely
> white.
>
> The bowl was, of course, opaque both in light and dark,
> and was thick enough so there was no element of
> transparency/translucency.
>
> My conclusion is we still need a better definition of
> whiteness.
>
> Ivor and Olive Lewis wrote:
> Dear Andrew,
> Yes, I recall the Gold Leaf Electroscope. Delicate things. The toys we
> played with long ago. Did you get to wind the Whimshurst Machine or
> rub the Electrophorous with a Cat Skin ?
> I do not think opacity, transparency and translucency are mutually
> exclusive because all rely on the transmission of light to some
> degree. As I read the observations, when internal reflection occurs at
> grain/grain interfaces or glass/bubble boundaries, then the light
> issuing from the surface increasingly takes on the character of
> jumbled light . No doubt this is complicated by defraction and other
> optical phenomena. Opacity and, if you wish, whiteness seem to be due
> to the return of light shining from the direction of the observer.
> Transparency is noted by the recognition of light coming from the
> opposite direction to the viewpoint of the observer. Translucency
> might be due to the interference of either by reflective and
> refractive interfaces, scattering light within the fabric. Just
> thoughts, but all testable.
> Best regards,
> Ivor Lewis
>
>
> ______________________________________________________________________
> ________
> 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.
>
> -- Steve Slatin -- Entry-level potter, journeyman loafer, master
obfuscator
> No website, no sales room, no scheduled hours
> All talk, no action
> Sequim, Washington, USA
> 48.0937°N, 123.1465°W or thereabouts
>
> ---------------------------------
> Do you Yahoo!?
> Friends. Fun. Try the all-new Yahoo! Messenger
>
>
____________________________________________________________________________
__
> 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.
Ivor and Olive Lewis on wed 9 jun 04
Dear Andrew,
Yes, I recall the Gold Leaf Electroscope. Delicate things. The toys we
played with long ago. Did you get to wind the Whimshurst Machine or
rub the Electrophorous with a Cat Skin ?
I do not think opacity, transparency and translucency are mutually
exclusive because all rely on the transmission of light to some
degree. As I read the observations, when internal reflection occurs at
grain/grain interfaces or glass/bubble boundaries, then the light
issuing from the surface increasingly takes on the character of
jumbled light . No doubt this is complicated by defraction and other
optical phenomena. Opacity and, if you wish, whiteness seem to be due
to the return of light shining from the direction of the observer.
Transparency is noted by the recognition of light coming from the
opposite direction to the viewpoint of the observer. Translucency
might be due to the interference of either by reflective and
refractive interfaces, scattering light within the fabric. Just
thoughts, but all testable.
Best regards,
Ivor Lewis
______________________________________________________________________
________
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.
Steve Slatin on wed 9 jun 04
Ivor --
As you know, I rarely question your science as I believe you
have a better handle on most pottery-related things than I do.
I will challenge your statement about whiteness, however.
I believe whiteness (as a characteristic) exists without light
coming from the direction of the observer.
I took a white bowl (porcelain, clear glaze) into a closet
with no windows and closed the door. With a highly
directional flashlight (maglight, AA type with the tiny
bulb and fairly well focused beam) at my feet, the bowl
appeared white. I moved it to 90 degrees from me around
the bowl, and stood it my original position. As far as the
'shadow' point on the bowl, it still appeared extremely
white.
The bowl was, of course, opaque both in light and dark,
and was thick enough so there was no element of
transparency/translucency.
My conclusion is we still need a better definition of
whiteness.
Ivor and Olive Lewis wrote:
Dear Andrew,
Yes, I recall the Gold Leaf Electroscope. Delicate things. The toys we
played with long ago. Did you get to wind the Whimshurst Machine or
rub the Electrophorous with a Cat Skin ?
I do not think opacity, transparency and translucency are mutually
exclusive because all rely on the transmission of light to some
degree. As I read the observations, when internal reflection occurs at
grain/grain interfaces or glass/bubble boundaries, then the light
issuing from the surface increasingly takes on the character of
jumbled light . No doubt this is complicated by defraction and other
optical phenomena. Opacity and, if you wish, whiteness seem to be due
to the return of light shining from the direction of the observer.
Transparency is noted by the recognition of light coming from the
opposite direction to the viewpoint of the observer. Translucency
might be due to the interference of either by reflective and
refractive interfaces, scattering light within the fabric. Just
thoughts, but all testable.
Best regards,
Ivor Lewis
______________________________________________________________________
________
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.
-- Steve Slatin -- Entry-level potter, journeyman loafer, master obfuscator
No website, no sales room, no scheduled hours
All talk, no action
Sequim, Washington, USA
48.0937°N, 123.1465°W or thereabouts
---------------------------------
Do you Yahoo!?
Friends. Fun. Try the all-new Yahoo! Messenger
Ivor and Olive Lewis on thu 10 jun 04
Dear Steve Slatin,
An interesting proposition. I use the same optical process to
determine the best way to orient certain gemstones to exploit their
optical properties, those such as Moonstone, Tiger Eye and Star Gems.
Total internal reflection from the interior of the gem serves as a
marker.
I agree about a definition for White. The best we seem able to achieve
is through comparison to natural objects; Snow, Swan Feathers, Sunlit
Clouds, Milk and so on.
Whiteness, in the context of a visible surface, might be thought of as
that which exhibits no discernible hue or colour yet is so brilliant
as to be without greyness. But, of course it is not possible to define
something by the absence of attributes, which leads us nowhere.
One of the factors you need to eliminate in your experimental
observation is the effect of light on your own eyes. Our eyes adapt
rapidly to changes in light intensity. As intensity falls the iris of
the eye dilates allowing more light to enter the pupil so things
appear to retain their brightness. Were you able to prevent that
reflex response your observations might have been different.
If you were to measure the intensity of whiteness of the bowl with a
Lightmeter you would record a higher value from the direct returned
light and a lower one from the oblique reflection. As a student I
would have had to use a "Grease Spot Photometer" and a "Standard
Candle" to achieve what can be done in seconds with a modern
photographic lightmeter.
Were you to have a high intensity source of light and make some very
thin bowls from the same Porcelain/Glaze combination it would be
interesting to see how well light is transmitted from the backside
towards you.
Thanks for making a contribution to this thread.
Best regards,
Ivor Lewis. Redhill, South Australia
Potters Council Member
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