Re: [Clayart] Talc Substitution

[David Woof]

Let's narrow the conversation to availability of Asbestos Talc vs Non-Asbestos Talc.

Since Raw Talc use is so pervasive in Industry and Manufacturing, including foods, tires, paints, plastics...........and that synthetic magnesium silicate does not provide the desired properties inherent in natural Talc, my initial search would be for providers and users of non-asbestos Talc. It isn't going away easily.

I only use 3 to 6 percent Talc in my clay bodies and while Wollastonite doesn't provide the Talc properties, I would increase the percentage of Wollastonite by that Talc percentage and not miss Talc if I had to!

Talc and Wollastonite are my "broad Spectrum Clay Body Antibiotics" so to speak.
At this rate including use in glazes, I have enough stored Talc to last beyond the rest of my, most likely, extremely long life time.
Stock up now while you still can if you have concerns.

(So Let the Talc Haters laugh while they kin "can"..... Let them piss in the wind) And Give you, their Talc!!!

Mel, you crafty old Viking! do you have some Talc to spare for this here Jeff Walker Gentleman?

Misneach,

David Woof.........I'll hang on to my Talc until "they" pry it from my cold and dusty claws...........................................
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From: Clayart <clayart...@lists.clayartworld.com> on behalf of Jeff D. Walker <jdwa...@silverdollarcity.com>
Sent: Saturday, October 2, 2021 9:03 AM
To: cla...@lists.clayartworld.com <cla...@lists.clayartworld.com>
Subject: [Clayart] Talc Substitution

Just wondering if anyone has started working on a true replacement for Talc? We don't use a lot of it but we do use it and since it seems to be going away I guess it's time to start working on the tests for its replacement.

Jeff Walker
HillCreek Pottery
Silver Dollar City
Branson, MO

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[ron...@ca.inter.net]

Hi Jeff,

I just calculated a cone 6 glossy glaze with Texas talc and used
dolomite to source the magnesium in a 2nd glaze. They have the same
expansion and Seger formula and should be stable when fired to cone 6
without a lot of colouring oxides. I would classify it as a good liner
glaze with a typical colour response to colouring oxides.

Frit 3134 - 20.0
Mahavir spar - 10.0
whiting - 15
Texas Talc - 10.0
EPK - 20.0
Silica - 25.0
Total - 100.0

Same glaze without talc.

Frit 3134 - 20.0
Mahavir spar - 9.0
whiting - 7.5
dolomite - 14.0
EPK - 20.0
Silica - 29.5
Total - 100.0

If anyone would like to fire them up please post the results to
Clayart. Do make up at least 1000 gram batchs to minimize any weighing
errors.

If anyone has a glaze with talc in it and would like me to convert it
using dolomite instead of talc send it to me. I would expect a report
back about how the exchange worked.

RR

Quoting "Jeff D. Walker" <jdwa...@silverdollarcity.com>:

> Just wondering if anyone has started working on a true replacement
> for Talc? We don't use a lot of it but we do use it and since it
> seems to be going away I guess it's time to start working on the
> tests for its replacement.
>
> Jeff Walker
> HillCreek Pottery
> Silver Dollar City
> Branson, MO
>
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Ron Roy
ron...@ca.inter.net
Web page ronroy.net

[ron...@ca.inter.net]

OK Jeff.

By the way two people have mentioned wollastonite as a source of MgO.
There is not enough MgO in wollastonite to be of use in this.

RR


Quoting "Jeff D. Walker" <jdwa...@silverdollarcity.com>:

> Thank you Ron. We fire cone 10 and I will get you a copy of the
> glaze I have been working with. Your help is invaluable to us all.
> Jeff
>
> ________________________________
> From: ron...@ca.inter.net <ron...@ca.inter.net>
> Sent: Monday, October 4, 2021 11:23:07 AM
> To: Clayart international pottery discussion forum; Jeff D. Walker
> Cc: cla...@lists.clayartworld.com
> Subject: Re: [Clayart] Talc Substitution

>> <https://lists.clayartworld.com/pipermail/clayart/attachments/20211002/9816cbb6/attachment.htm<https://lists.clayartworld.com/pipermail/clayart/attachments/20211002/9816cbb6/attachment.htm>>
>>
>
>
>
> Ron Roy
> ron...@ca.inter.net
> Web page ronroy.net<http://ronroy.net>

[David Woof]

Hi Ron,
Just to keep the record clear: I was talking about my use of Wollastonite in my Clay Bodies and not extolling Wollastonite as a sub for Talc in formulating glazes.

And I do not, would not, include Wollastonite in my clay bodies for its meager contribution of MgO.

Why I do include Wollastonite, and have experimented with and used Wollastonite (CaSiO3) since early 1980's has nothing to do with substitution of Talc.

And kudos for your efforts and in discerning that Jeff was concerned with subbing Talc in glazes, served him up the answer he was looking for.

Misneach my friend, Soldier on..........

David Woof....................Keep your GO BAG packed!!! being a 4th generation Alien Resident in my Native Land has taught me: "Never live anywhere you can't leave.....Never own or possess anything you can't leave behind."
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________________________________
From: Clayart <clayart...@lists.clayartworld.com> on behalf of ron...@ca.inter.net <ron...@ca.inter.net>
Sent: Thursday, October 7, 2021 8:26 AM
To: Jeff D. Walker <jdwa...@silverdollarcity.com>
Cc: Clayart international pottery discussion forum <cla...@lists.clayartworld.com>

URL: <https://lists.clayartworld.com/pipermail/clayart/attachments/20211009/f0ff6384/attachment.htm>

[David Woof]

Hi Everyone,
Regarding the direct substitutions as given by Glaze Calculation programs.
It must be understood that each of the minerals used in Ceramics have important individual characteristics and properties, which also carry consequences, either positive or negative, when one attempts to substitute without informed consideration.

One such well known is that CaCo3, Calcium Carbonate (whiting) in certain amounts in concert with other certain mineral combinations will cause pin holes in the fired glaze.
Substituting Wollastonite CaSiO3,..... for the CaCo3 and adjusting the other glaze ingredients for a new balanced formula will (in most cases) eliminate the pin holes.
But the resulting glaze would probably not display the same characteristics as the original,..although if successful, one would have created a New Glaze!!!"

Another example I will cite is of the mineralogy of Wollastonite which could be in its own right a valuable material in many applications but is often underrated and misunderstood by potters.
But not by Industry which always uses the most cost effective and results efficient materials.

Wollastonite offers much more to a clay body or glaze than simply as a convenient source of, or substitution for, calcium and silica (or as a minor fluxing agent) as Glaze Calculation Programs would have one believe!!!

In its mineral state Wollastonite occurs as bladed crystal masses and the separated crystals often show an acicular particle shape.
Its acicular structural crystalline character provides a "dimensional stability" and what is termed a 'flexural modulus" to materials it is added to.

(Read: Of significant importance to Potters and Ceramic Industry is that at our firing temperatures, the Flexural Modulus properties of Wollastonite are maintained in the clay body from wet plastic throwing state, thru the drying stages to the bone dry pre firing...and during the firing all the way up and then down into the cold out of the kiln fired ware state.

It is not difficult to translate this to beneficial reasons for application in our glazes and clay bodies* before * during* and post firing*

In simple description , in its crystalline structure Wollastonite works as twined and interlaced "little rollers" **rather** than as needles jumbled together to tack and pin the clay particles together as in the "fabled and inordinately popularized" KYANITE.
Kyanite does this well for a Raku body in the forming stage (as well as its potential to tear skin!!!)
Kyanite also contributes problematic free silica in fired stoneware bodies!!!

Slowing down and thinking, learning, prevents much wondering, failures and frustration... let's not just seek answers for a pressing hurry up immediate need or glaze fix.

Study, learn, appreciate the intrinsic qualities, then make wise effective use of our materials.

Misneach,

David Woof..................................................................................................................
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[David Woof]

Hi Everyone,
Let's agree to use previously mentioned Kyanite as a Ceramic material comparison. And let's agree that those who swear by Kyanite will also admit the struggles with its limitations.

Bear with me while I present a comparison favoring substitution with Wollastonite (CaSiO3) which does not cause these problems at the pyrometric cone temperatures we work at.

In fact of comparison; cone 03/02 is threshold for dissociation of the combined mineral elements for Kyanite, vs cone 19 for Wollastonite.

And as I mentioned in the accompanying previous post #1, the Flexural Modulus properties of Wollastonite are maintained in the clay body from wet plastic throwing state, thru the drying stages to the bone dry pre firing...and during the firing all the way into the cold out of the kiln fired ware state.

Wollastonite has been tested and used in Industrial Ceramics for many years now, and in many other Industrial manufacturing applications including plastics, paints, and roofing materials in part because of this flexural modulus property. (Fancy words for saying it can flex and resist breaking)

Following; is a bit of the science behind what I have been passionately saying about and why I use it.

At temperatures above 1100 c/2012f (cone 02) Kyanite decomposes into Mullite and a Vitreous Silica in the reaction 3(Al2 O3*SiO2) > 3Al2 O3*2SiO2+SiO2. This dissociated transformation results in expansion of the vitreous silica which is the cause of the cristobalite we attempt to avoid in our stoneware when held at temps above cone 02 for long periods. Especially in slow ramp firing.

**** Also, If we feel we must add fillers to a clay body there are other more innocuous materials than the raw ground silica/flint flours and fine silica grits as these also compound the free silica potential to cause cristobalite formation.

In contrast: Wollastonite begins its melt at 1540 c / 2804 f (cone 19)
The then molten CaSiO3 continues to maintain a tetrahedral SiO4 local structure up to 2000c /3632 f which takes us off the cone charts of where we fire any of our clay bodies. This extremely high eventual disassociation of the Calcium/Silica bond in Wollastonite is of no practical concern in our use as a valued glaze or clay body constituent.

And for the above reasons I have used Wollastonite in my Wood-Fired to cone 16 bodies, Gas fired cone 10, Electric fire to cones 6 to 10 and a bullet proof Raku body at whatever temp as well.
And although Kyanite is generally recognized as a relatively effective but ("bare hands grinding") Raku Body, I have shunned Kyanite because of its inherent limitations in favor of the " stand up, smooth move" pleasure and protective confidence experienced with Wollastonite at all temps and firing protocols.

Ok! Ok! I've kicked this dead horse to death a second time! I know!!!!
Well almost...
The foregoing is well worth the second read and pondering for those who admit that they don't already know it all... or are no longer content with knowing "just enough" until they get in knee deep sh-- and yell "help me" on Clayart.

Misneach,

David Woof,..................
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[Robert Harris]

David, I have never found any references that say that Kyanite converts to
mullite at such low temperatures. Almost all the ones I've found indicate
that conversion happens above 1300C (2372F). I have often wondered if the
Kyanite to Mullite conversion actually happens in our clays, or if it does,
whether it is somehow propogated by the other constituents of the clay. (I
imagine most of the data documenting conversion is done on fairly pure
kyanite samples). Do you remember where you got that number from?

This is an interesting paper
http://ijmse.iust.ac.ir/article-1-379-en.pdf
which also shows that complete conversion to mullite requires several hours
(below 1500C (2732f) - it occurs rapidly (30 mins) at 1600C (2912F).

Commercially Kyanite is converted to Mullite by heating for many hours at
1300C (2372F). So while it's possible that Kyanite will start converting at
Cone 10 temperatures, only a very very small percentage will be converted
under ordinary firing conditions. (Perhaps in a 5 day wood firing far more
will be converted, but that is a special case!)

The kyanite to mullite conversion is a very different process from
wollastonite melting. (Or any melting. It is irreversible conversion from
one crystalline form into another crystalline form). The majority of our
clay and glaze materials melt at temperatures far in excess of those we
fire to. This is the very essence of eutectics. I know very little of the
physical process of sintering, and then melting, but presumably at particle
interfaces eutectics come into play. So, of course one can get wollastonite
to melt at far lower temperatures than 1540C. I just made up a very molten
celadon that gets most of its calcium and magnesium from Wollastonite and
Talc. It is the interaction between wollastonite and feldspar that melts at
low temperatures. And both of those exist in clays too.

Robert

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[David Woof]

Hi Robert,
You hit it on the head when you mentioned "Eutectics" as being the tools most often confounding a simple statement regarding the numbers from a tested material in its pure mineral form.

I said in part;......***"In simple description , in its crystalline structure Wollastonite works as twined and interlaced "little rollers" **rather** than as needles jumbled together to tack and pin the clay particles together as in ........... KYANITE.

Kyanite does this well for a Raku body in the forming stage (as well as its potential to tear skin!!!)

Kyanite also contributes problematic free silica in fired stoneware bodies!!! "***

I should have clarified my reasoning that our use of fluxes in stoneware bodies and the eutectics that at times draw more refractory fluxing materials and the kyanite silica into lower time/temp melts.
And that as these kyanite "rollers" begin to melt they are of no further use in strengthening the firing clay body.

Robert, Because of these variables in applications, my intent was to provide enough information to inspire further investigation and I am perhaps remiss in not providing a clarification of my intent.
I don't want now to use time to provide for a deeper discussion when anyone truly interested can easily obtain same.

Our numbers are the same or similar, just our interpretation of application and processes arrive at differing conclusions.

Our reasoning and personal application of the information requires a much deeper study and my intent was never to write a paper subject to peer review.
Understanding the basics of the variable results eutectics play........much like one receiving implanting of a fertilized ovum knowing only that the male/female donors were both human. So unlikely that the little "it" will come out furry and sporting a tail.

The genetics of recessive and dominate genes and the variableness of combined DNA information being as it were the "eutectics."
( This is a generalized example only: don't anyone go off the deep end arguing anything about Genetic Science, or little monkeys! )

Robert, You hit it on the head when you mentioned eutectics as being the tools most often confounding a simple statement regarding the numbers from a tested material in its pure mineral form.

Misneach,

David Woof.................Keep your GO BAG packed!!! Being a 4th generation Alien Resident in my Native Land has taught me: "Never live anywhere you can't leave.....Never own or possess anything you can't leave behind." But walk tall and live full and large where ever you find yourself and hang your hat!!!.
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________________________________
From: Clayart <clayart...@lists.clayartworld.com> on behalf of Robert Harris <robert...@gmail.com>
Sent: Tuesday, October 19, 2021 11:13 AM
To: Clayart international pottery discussion forum <cla...@lists.clayartworld.com>
Subject: Re: [Clayart] Was Talc Substitution, Now Wollastonite #2 (a continuing of 2 posts)

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