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#21 JBaymore

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Posted 08 October 2013 - 01:50 PM

Luca,

 

A liability concern on the flaking is that the edges of the flaked area will be razor sharp. 

 

And yes, I would imagine that IF the glaze layer "loosens up" on the body over time (it won't be "sudden") the acoustic resonance of the enclosure would likely slowly change also.

 

In the finish firing ("glazefiring") , if it is essentially to the same cone endpoint as the "bisque" firing... the additional shrinkage will be minimal < 1%.  You really will not be changing the body much.

 

You issue is keeping the acoustic resonance of the earthenware open structure NON-vitrified body while gaining the structural integrity you desire.  Even if you remain at "low temperature"...... if you start to vitrify the body (it can be done) ..... the resonance will change.

 

best,

 

..........................john


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#22 PeterH

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Posted 08 October 2013 - 05:24 PM

Luca,

 

I not really qualified to answer your questions, but here are some guess-timates:

>So I may get a better sense of this, what kind of percentages for shrinkage might typically occur in earthenware for:

>1) the first bisque firing (6% or so, for example?) and then...

>2) the second firing after glazing (an additional say 3% for a cumulative total of 9%, for example?) and...

AFAIK you're in the right ballpark, there is also shrinkage from forming to being air-dry. [This is low for dry-pressed ware.]

>3) are the temperatures and time the same for both stages of firing? 

>This assumes firing to maturity in the end.

No and yes-ish. The bisque firing takes the pot very slowly through some risky parts of the firing (e.g. getting rid of chemically

combined water, burning out organics, etc.). The end temperature of the bisque is probably chosen so that the absorbency

of the bisque pot is optimal for dip-glazing. The "glaze" firing can go rapidly through the lower temperatures, but then needs

to reach sufficient temperature -- for sufficient time -- to mature the pot "as desired". AFAIK this ends up with the two firings

taking comparable times. But actual firing schedules depend on the body material, the kiln, and to some extent the whims of

the potter and his/her kiln-controller.

>It is hoped that tolerances can be reliably kept within +/- 1% after shrinkage, after the entire process has been tested.

This is an area where you do need a consultant in technical ceramics. If resonant cavities are involved remember 1% linear

is 3% volume.

 

Regards, Peter

 

You may find acquiring a general reference work, such as The Potter's Dictionary of Materials and Techniques helpful.

http://tinyurl.com/posz3ac

 

Two other surface treatments you might like to consider are Parian and salt-glaze.

 

Parian is a sort of self-glazing porcelain casting body. So named because of its visual similarity to Parian marble.

http://tinyurl.com/oszwb9u

 

Salt-glazing is a specialist technique that gives a very thin surface film of glaze, sometimes pitted in

an orange-peel effect, most usually associated with historic German beer steins and sewer-pipes. Its

a specialist process, which gives a covering that is often attractive and usually very dirt-resistant [and

you do rather want dirt resistance in a sewer pipe].

http://tinyurl.com/o2ac2rb

... perhaps in your case the less obtrusive effects would be appropriate

http://tinyurl.com/pr9hbq5

http://tinyurl.com/plu84dj

http://tinyurl.com/pw5tcb6



#23 PeterH

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Posted 08 October 2013 - 05:58 PM

FYI http://www.torontost.../horn-of-plenty

 



#24 JBaymore

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Posted 08 October 2013 - 06:21 PM

PeterH,

 

My friend MATUMIYA Ryoji-san made a huge one of these that looks like a fish back in July while I was working at Kanayama for the summer.  It works REALLY well.

 

http://blog.livedoor...ywando3350/?p=5

 

about 80% down the page.  Sorry all in Japanese.

 

best,

 

...........................john


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Professor of Ceramics; New Hampshire Insitute of Art

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#25 bobzchemist

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Posted 09 October 2013 - 05:20 PM

As a cosmetic chemist, I have worked with iron oxides professionally for a long, long time. As a potter, I've only tried incorporating them in my work recently, so I can say that a buff/brown color is definitely achievable (but may take some work to develop). Using an iron oxide wash made with the micronized, sub-micron, or even nanoparticle size oxides used in high-end cosmetics (much, much smaller than commercial iron oxide washes) should allow the iron oxide particles to seal up some or all of the porosity of the outside surface of the bisqueware without affecting the acoustic properties or strength of the clay instrument. A pleasing variation in exterior color could be achieved by either brushing or spraying a somewhat variable combination of oxides onto each piece. Restricting the porosity should reduce the oil-absorbency you are concerned with.

 

Depending on how high you wind up firing these objects, burnishing the outside surfaces might also work (although I don't believe burnishing would lend itself easily to mass production)

 

Let me know if you want sources of supply for these specialized oxides.

 

Bob Zonis



#26 Mart

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Posted 10 October 2013 - 03:33 AM

That was very interesting read.
Are you guys planning to build a high end ceramic loud speakers?
Look up Estelon, they used marble based composite to build their super expensive loud speakers.

#27 luca

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Posted 10 October 2013 - 01:11 PM

John, what a fantastic experience that must have been, working in Kanayama. I've just returned from Kyushu and have been reading up on the influence of Korean pottery in origins of the Japanese pottery industry, and the fascinating history surrounding abducted Korean potters. I'd certainly love to spend a period of time under the tutelage of a Japanese craftsman, in ceramics, or another field....all artists, designers, and craftsman stand to benefit from such high-level commitment to the art that is commonplace in Japan.

 

For this venture, I am largely opposed to the ornamentation of glazing, preferring the 'honesty' of the underlying material, and therefore only necessarily interested in glazes to cope with the issue of oil-absorbency. This is why a clear matte glaze is the focus. I'm very opposed to the slickness of gloss glaze, and the colouring of the material, preferring instead honesty and purity and texture, without any 'barrier' if you will, obstructing touch.

 

As an alternative solution to glazing, some experimentation has been done with firing to maturity once and then coating with a clear petroleum-based solvent-like formula, which is highly transparent and alters the texture of the surface only very minimally. Drawbacks (known thusfar): odour, and moderately effective surface protection. Formulas we're aware of all carry an odour that is unendurable for home interior products, though with time, fades. 

 

Bob Zonis, concerning oxides, though the colouring of the exterior is less appealing as mentioned, if no other high-performing solution can be found that meets the specified criteria, then abandoning the colour-in-the-body constraint may be necessary. I've been using oxides in past experiments to colour the earthenware body either sandy tones or grey, with success, but this process surely is different from what you have suggested. How does the oxide wash that you speak of function to seal the porosity and how does burnishing achieve this (or were you suggesting burnishing solely as a means to create texture?)

 

Peter, I'm going through the info in the links supplied (thank you) but let me just first ask directly, can salt glazing be done with earthenware? I should think so, as the pipes you mentioned, are typically a kind of terracotta (earthenware then) no? Parian, on the other hand, would seem to be ruled out as it is a porcelain casting body, thus a high-fire vitrifying body, which won't meet the acoustic requirements.

 

With kind regards,

Luca



#28 PeterH

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Posted 10 October 2013 - 01:48 PM

>Peter, I'm going through the info in the links supplied (thank you) but let me just first ask directly, can salt glazing be done with earthenware? I should think so, as the pipes you mentioned, are typically a kind of >terracotta (earthenware then) no?

 

I don't really know. The salt-glazing craft potters tend to like high-fire, but AFAIK that's an artistic decision

rather than a technical one.

 

A quick google gives this, if you have access to the full paper it may mention actual temperatures, but

the abstract says: Clays containing a high iron oxide content should be salt glazed at low temperatures.

http://onlinelibrary...3883.x/abstract

 

Regards, Peter



#29 JBaymore

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Posted 10 October 2013 - 02:30 PM

High iron bodies and earthenware are a non-starter for the traditional slat glaze process.  The above process is a "technicallitty"... not practical for production situations.

 

best,

 

..............john


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Professor of Ceramics; New Hampshire Insitute of Art

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#30 PeterH

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Posted 10 October 2013 - 06:31 PM

>JBaymore

>High iron bodies and earthenware are a non-starter for the traditional salt glaze process.

 

Luca, please ignore my suggestion about salt-glazing your artefact.

 

Regards, Peter

 

John,

 

Independently of the purpose of this thread I would like to understand where the lower temperature end of practical

salt-firing is/was positioned, and would welcome any leads.

 

For example, the 1958 US patent 2855655 Salt glazing ceramic wares says:

It is not practical to glaze the wares at a temperature much below 1900 F (1038C to us brits).

https://docs.google....s/US2855655.pdf

... 2nd non-figure page, right-hand column (numbered 4), line 8 to give the full ref

... so presumable the author expected somebody to be interested in salt-glazing something at quite low temperatures.

 

Which is certainly not suggesting that any such activity was part of the traditional salt glaze process, as exemplified by

the long history of salt-glazed stoneware starting in Germany in the 13th century.

 

Regards, Peter

 

PS Looking closely at a picture of a very red salt-glazed drain pipe, I'm forced to conclude that it contains less iron than

I'd originally assumed:

http://tinyurl.com/pnan6an

 

 

 



#31 JBaymore

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Posted 10 October 2013 - 08:12 PM

Paul Soldner was doing "lowfire salt" as low as in the cone 08-09 range and a lot at at 04-05.... but to call it "salt glaze" as the usual understanding is of that term is not really accurate.  The effect is more like what one gets in open pit firing with salt and other such additives.  (Do a visual image search.)

 

To really "seal" the clay surface with "salt glaze" you have the body vitrified enough to have the sodium fluxed silica active and melting.  That paper is pretty accurate.

 

And salt glazed ware is ALL crazed to beat the band (high COE of the soda fluxed glass).  Soda glazing came about at a time when such concerns were  not all that great... plus it was a labor saving process that allowed quick production of glazed ceramics.  When you add in high iron to the body and salt glaze there is a great tendency to developing a really brittle body.  Plus the iron tends to resist the salt.  And if there is much reduction....... it gets REALLY brittle and REALLY brown.

 

I did a lot of salt glazing in the mid to late 70's.  Fast cool the kiln and you get grey..... slow cool and you get browns.  And MAN..... uranium oxide gived fantastic oranges in salt glaze!!!!!!!

 

The glass layer with the crazing alone likely would be impacting the sonic properties.  And he is not looking for a "tight" body.

 

best,

 

.................john


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Professor of Ceramics; New Hampshire Insitute of Art

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#32 luca

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Posted 11 October 2013 - 05:41 AM

Yes, that's correct, experimentation over the preceding year and a half indicates that vitrification is undesirable for our application. Granted, this is not a stark day and night difference (others do use porcelain), however, the low-fire still-porous bodies do outperform porcelain and stoneware, to my ears. The concept also resonates with us on an intuitive/emotional level with our associations to harsh, glassy tones and and materials that embody this.

 

Could anyone suggest, just to get us started, a clear matte glaze suitable for earthenware that they may have had experience and pleasing results with? 

 

Kind regards,

Luca



#33 JBaymore

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Posted 11 October 2013 - 12:57 PM

Clear and matte are another set of conditions that tend to be "mutually exclusive".  The mattness of most glazes is caused by some cooling cycle devitrification of the glaze melt.  This causes small alumino-silicate crystals to deposit/form on the surface of the glaze.  The likely problem here is that they are then not "clear"....as in a transparent window glass kind of thing. 

 

The other ways matts are sometimes done is to effectivlly underfire the glaze.  But those too are not "clear" transparents due to the un-melted components.

 

Yet anotehr is the alumina matts..... which MAY be the direction to go... they are clay-ie surfaces.  But typically they have a "harsh hand" so my guess is you wouldn't like them for that characteristic....... not to mention that they are also not transparent.  This kind of surface is often used for non-slip kinds of surfaces for floor tiles.

 

What you might be wanting is an earthenware glaze that looks like unglazed earthenware.  ;)

 

Have you considered something as simple as sealing the earthenware with something like wax?

 

best,

 

.....................john

 

PS:  The nano-particle thing alreaady mentioned sounds intreiguing..... I have no experience with them because they are relatively new and the fine-ness of those materials makes the health and safety issues a bit larger from a dust control perspective.  Interested to hear any results.


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Professor of Ceramics; New Hampshire Insitute of Art

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#34 Benzine

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Posted 12 October 2013 - 08:46 AM

John, I have no idea what you are saying sometimes, but I like reading it.
"Anything worth believing, is worth questioning"

#35 luca

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Posted 13 October 2013 - 02:42 PM

Yes, there's been some experimentation with wax, and will experiment further with other varieties of wax. The product is intended to be in four colours - white, sandstone, grayish concrete, and black. Beeswax left a yellow cast on the white model, the primary model colour, which was unappealing, but also altered the texture/feel significantly, so even though the colour cast was acceptable on the darker colours, the surface texture was diminished. Unglazed earthenware with a very subtle granular tactile quality is very much the the ideal, target texture.

 

"What you might be wanting is an earthenware glaze that looks like unglazed earthenware." - Indeed. Sufficiently clear and matte sounds to be a problem. 

 

Regarding the alumina matte glazes, what was meant by your description of them as having a "harsh hand"...are they extremely rough and textured? 

 

And though no ideal glaze for this application comes to mind, are there any mostly clear matte glazes that others can recommend, just for experimentation, and to confirm whether it may work for any the planned colours? Thank you.

 

Kind regards,

Luca



#36 bobzchemist

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Posted 18 October 2013 - 04:22 PM

Luca,

 

1) Regarding the iron oxides - saying that the earthenware is porous means that it has pores (holes) and channels in the clay. The purpose of the iron oxide coating would be two-fold - it would reduce the porosity of the earthenware by physically filling the exterior pores, and it would impart color. This could be sealed onto your piece by a wax coating (if you apply the iron oxide after firing), or could be incorporated into the clay body by applying an iron oxide dispersion to your greenware. Applying the oxides after firing would give you greater control over the color. Because it's just a surface coating, It shouldn't affect the acoustics too badly. BASF makes high-end iron oxides (also referred to as "transparent" iron oxides) http://www.basf.com/...brand/SICOTRANS and so does Rockwood http://www.rpigments.com/Products, to name just a few suppliers.

 

2) Wax does not have to be dissolved into nasty-smelling solvents. It's just usually done that way because those solvents are cheaper. Talk to the folks at Koster Keunen for information on waxes, natural waxes and possible suppliers of wax/solvent mixtures http://kosterkeunen.com

 

3) Burnishing pottery does the same sort of thing I was suggesting with the iron oxides - superfine particles seal the surface and fill the pores - but in this case they're clay (terra sigilata). Of course, there's more to it than that:

 

http://ceramicartsda...ishing-pottery/

 

http://ceramicartsda...ishing-pottery/



#37 mrfixit08

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Posted 18 March 2014 - 07:18 PM

I found this link, which I think might be of interest to you.

 

http://digitalfire.c...drate_2271.html






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