DJBrewer88 on sat 8 may 10
I have Stephen Murfitt's Glaze Book and have found some terminology
differences. One ingredient called for in some recipes is quartz. Is
this the same as flint or silica?
DJ
Steve Mills on sun 9 may 10
Dear DJ,
the short answer is: Yes!
However there are also some corrections which you (and others) will need to
know.
Because this book was written for the publishers on a "once only" fee basis=
,
there were some errors in the final publication which Stephen was unable to
do anything about!
I have listed them below:
*Stephen Murfitt Glaze Book Corrections***
Page 128: Top tile: should read: Recipe A applied over, not 50 / 50
Rec=
ipe
B: plus 10 % red iron oxide
Page 128: Middle tile: Same changes as top tile
Page 128: Bottom tile: Should read: Recipe B plus 10% red iron oxide=
,
over Recipe C plus 10% red iron oxide, then recipe A applied over both.
Page 129: Bottom tile: should read: Recipe A over recipe B, plus 10=
%
red iron oxide.
Page 150: Middle tile: should read: Recipe A plus 3% Rutile, over
recipe B plus 10% red iron oxide.
Page 172: Top tile: should read: Recipe A plus 3% Rutile, over
recipe B plus 5% red iron oxide.
Page 268: Delete Cobalt Carbonate and Red
Iron Oxide.
At Bath Potters Supplies we used to include this list with each copy we
sold.
I hope this helps everyone who has a copy.
Steve M
On 9 May 2010 01:36, DJBrewer88 wrote:
> I have Stephen Murfitt's Glaze Book and have found some terminology
> differences. One ingredient called for in some recipes is quartz. Is
> this the same as flint or silica?
>
> DJ
>
--
Steve
Bath
UK
www.mudslinger.me.uk
Growing old is inevitable, growing up is optional!
Ron Roy on sun 9 may 10
Hi DJ,
Quartz - what we get here in North America - is almost pure silica.
Flint was (still is?) what is used when silica is called for in
England and has some impurities.
We are used to subbing quartz (silica) in all recipes that call for Flint.
From Glazes for the p[otter by Cooper and Royle
Quartz - SiO2 99.5, Al2O3 0.13, Fe2O3 0.06, Loss on Ignition 0.17
Flint - SiO2 98.6, Al2O3 0.26, Fe2O3 0.02, CaO 0.47, K2O 0.11, Na2O
0.01, LOI 0.33
Would you see any difference in a glaze made with one or the other - I
don't think so.
RR
Quoting DJBrewer88 :
> I have Stephen Murfitt's Glaze Book and have found some terminology
> differences. One ingredient called for in some recipes is quartz. Is
> this the same as flint or silica?
>
> DJ
>
Dan Parenteau on sun 9 may 10
Hello all, long time lurker first time poster.
This has been a vexing question for me as a beginning potter. In trying
to formulate cone 10 stoneware bodies I've been researching recipes and
I often get tripped up by this same question.
I picked up some old copies of Studio Potter and the June 1981 issue has
an article by Jim Robinson titled "Fear of Silica" where he indicates
flint is more likely to form cristobalite than quartz. He then goes on
to say that in "American publications, when flint is called for ground
quartz has been used", which seems to agree with Ron's statements.
That in mind, we now we get to my question: why do some raw material
suppliers list their products as flint?
e.g. Continental Clay lists "Flint - powdered 325m" and Laguna lists
"SILICA: Also known as Flint. Available in 200 and 325 mesh." I suspect
at this point you will all suggest I call the supplier and ask,
something which I haven't gotten the gumption to do yet.
Also, when adding larger mesh silica sand as "fine grog" to a throwing
clay body, does that "count" as increasing the silica content of the
recipe chemically or are the particles large enough to escape fluxing at
temperature?
Any feedback is appreciated!
- Dan Parenteau
Ron Roy wrote:
Hi DJ,
Quartz - what we get here in North America - is almost pure silica.
Flint was (still is?) what is used when silica is called for in
England and has some impurities.
We are used to subbing quartz (silica) in all recipes that call for Flint.
From Glazes for the p[otter by Cooper and Royle
Quartz - SiO2 99.5, Al2O3 0.13, Fe2O3 0.06, Loss on Ignition 0.17
Flint - SiO2 98.6, Al2O3 0.26, Fe2O3 0.02, CaO 0.47, K2O 0.11, Na2O
0.01, LOI 0.33
Would you see any difference in a glaze made with one or the other - I
don't think so.
RR
Quoting DJBrewer88 :
> I have Stephen Murfitt's Glaze Book and have found some terminology
> differences. One ingredient called for in some recipes is quartz. Is
> this the same as flint or silica?
>
> DJ
>
Ellen Currans on sun 9 may 10
When I organized my first glaze mixing area back in the early 70's, I=3D20
used
gallon milk jugs with the tops partially cut off to hold the most common
chemicals. I stored them two deep on shelves with the most used on
the outside, and found them very easy to use when testing. Just grab
a jug by its handle, (No lid to take off) and scoop out the needed=3D20
amount
into the gram scale on a wider shelf above the jugs. Oxides and stains
are kept in smaller jugs with lids on higher shelves, but all is =3D20
within reach
making for easy and quick test mixing.
The point of all the above is to say that I am using the same jugs now
that I started with, and one of them has FLINT written in heavy marking
pen, and then crossed out, followed by QUARTZ, crossed out, and
for the past l5 or so years SILICA. The name has more to do with the
usual usage in books and recipes and that has changed over time.
On the other hand, I also have some complicated correspondence
on file from Jim Robinson back in the 80s, concerning varieties of
quartz and which were best suited for use in clay to avoid forming
cristobolite and other firing problems. He wrote several articles for
Studio Potter, and I paid attention at the time - would again if I were
reworking my clay body.
Ellen Currans
Dundee, Oregon
PS. I have never had any problems from lidless containers for
the common glaze chemicals. A little dust may accumulate over the=3D20
years
and a few cobwebs on the least used, but that has never been
a problem. My studio is heated by a wood stove and an auxiliary
gas heater. We keep the bulk bags in an adjacent unheated storage.
-----Original Message-----
From: Ron Roy
To: Clayart@LSV.CERAMICS.ORG
Sent: Sun, May 9, 2010 3:18 pm
Subject: Re: quartz =3D3D silica?
Hi DJ,=3DC2=3DA0
=3DC2=3DA0
Quartz - what we get here in North America - is almost pure silica.=3DC2=3D=
A0
Flint was (still is?) what is used when silica is called for in=3DC2=3DA0
England and has some impurities.=3DC2=3DA0
=3DC2=3DA0
We are used to subbing quartz (silica) in all recipes that call for=3D20
Flint.=3DC2=3DA0
=3DC2=3DA0
From Glazes for the p[otter by Cooper and Royle=3DC2=3DA0
=3DC2=3DA0
Quartz - SiO2 99.5, Al2O3 0.13, Fe2O3 0.06, Loss on Ignition 0.17=3DC2=3DA0
=3DC2=3DA0
Flint - SiO2 98.6, Al2O3 0.26, Fe2O3 0.02, CaO 0.47, K2O 0.11, Na2O=3DC2=3D=
A0
0.01, LOI 0.33=3DC2=3DA0
=3DC2=3DA0
Would you see any difference in a glaze made with one or the other - I=3DC2=
=3D
=3DA0
don't think so.=3DC2=3DA0
=3DC2=3DA0
RR=3DC2=3DA0
=3DC2=3DA0
Quoting DJBrewer88 :=3DC2=3DA0
=3DC2=3DA0
> I have Stephen Murfitt's Glaze Book and have found some terminology=3DC2=
=3D
=3DA0
> differences. One ingredient called for in some recipes is quartz. Is=3DC=
2=3D
=3DA0
> this the same as flint or silica?=3DC2=3DA0
>=3DC2=3DA0
> DJ=3DC2=3DA0
>=3DC2=3DA0
=3D20
Ron Roy on mon 10 may 10
Hi Dan,
There is a later article by Peter Sohngen in Studio Potter Volume 28 #1.
In essence his research (I did the dilatometery) shows you need at
least 10% spar and go easy on micro fine silica (what we usually get
in the bag.)
Graded silica - like 200M with few fines is not a problem.
The more iron involved the more complicated the problem becomes.
This is about the fine quartz which is what we get now - no matter
what it says on the bag. You can find graded silica but that is not
what is shipped unless you specify the mesh size you want. The 200
mesh and 325 mesh are mostly micro fines and do turn into cristobalite
easily - unless - as Peter found out - you have enough spar (at least
10%) to melt the micro fine stuff.
I don't even recommend silica in cone 10 clay bodies anymore - there
is still enough free quartz in the clays we use to help with crazing.
Kyanite is a better product for high fire ware.
Why do suppliers list silica as flint - good question - the correct
label would be crushed quartz.
RR
Quoting Dan Parenteau :
> Hello all, long time lurker first time poster.
>
> This has been a vexing question for me as a beginning potter. In trying
> to formulate cone 10 stoneware bodies I've been researching recipes and
> I often get tripped up by this same question.
>
> I picked up some old copies of Studio Potter and the June 1981 issue has
> an article by Jim Robinson titled "Fear of Silica" where he indicates
> flint is more likely to form cristobalite than quartz. He then goes on
> to say that in "American publications, when flint is called for ground
> quartz has been used", which seems to agree with Ron's statements.
>
> That in mind, we now we get to my question: why do some raw material
> suppliers list their products as flint?
>
> e.g. Continental Clay lists "Flint - powdered 325m" and Laguna lists
> "SILICA: Also known as Flint. Available in 200 and 325 mesh." I suspect
> at this point you will all suggest I call the supplier and ask,
> something which I haven't gotten the gumption to do yet.
>
> Also, when adding larger mesh silica sand as "fine grog" to a throwing
> clay body, does that "count" as increasing the silica content of the
> recipe chemically or are the particles large enough to escape fluxing at
> temperature?
>
> Any feedback is appreciated!
>
> - Dan Parenteau
>
> Ron Roy wrote:
>
> Hi DJ,
>
> Quartz - what we get here in North America - is almost pure silica.
> Flint was (still is?) what is used when silica is called for in
> England and has some impurities.
>
> We are used to subbing quartz (silica) in all recipes that call for Flint=
.
>
> From Glazes for the p[otter by Cooper and Royle
>
> Quartz - SiO2 99.5, Al2O3 0.13, Fe2O3 0.06, Loss on Ignition 0.17
>
> Flint - SiO2 98.6, Al2O3 0.26, Fe2O3 0.02, CaO 0.47, K2O 0.11, Na2O
> 0.01, LOI 0.33
>
> Would you see any difference in a glaze made with one or the other - I
> don't think so.
>
> RR
>
>
> Quoting DJBrewer88 :
>
>> I have Stephen Murfitt's Glaze Book and have found some terminology
>> differences. One ingredient called for in some recipes is quartz. Is
>> this the same as flint or silica?
>>
>> DJ
>>
>
Dan Parenteau on wed 12 may 10
Thanks for the response Ron, a couple follow ups if you're game.
ronroy@ca.inter.net wrote:
> There is a later article by Peter Sohngen in Studio Potter Volume 28 #1.
> In essence his research (I did the dilatometery) shows you need at least
> 10% spar and go easy on micro fine silica (what we usually get in the bag=
.)
Just re-read that article, which I originally read a few months back and
didn't quite parse at the time. I think what you're saying is that
Peter's "Body 12", which has spar but no quartz and comes close to the
expansion properties of his "Body 7", is an example of a high fire
stoneware body which has no added silica yet exhibits the glaze fit
qualities desired. Obviously I've got a few more years of clay body
formulation experience in my future, but out of curiosity, how much does
a dilatometer test normally cost?
> Graded silica - like 200M with few fines is not a problem.
From what I've read much of what is sold as 200M is in fact only a
small percentage 200M and contains a larger percentage of finer size
particles. I think I'm suffering from being a few degrees of separation
from the raw materials. Peter's screen analysis of available forms of
quartz seems like an example of a first step to a better understanding
of what exactly I'm using.
> Kyanite is a better product for high fire ware.
Hmm, now I have something else to ponder. Kyanite, aka Sillimanite, as
far as I can tell this might be something used as grog or filler to open
up a clay body? What mesh size might one recommend for a throwing body?
Thanks again, Dan.
Ron Roy on thu 13 may 10
Hi Dan,
Use the 100 mesh kyanite to replace silica - the problem with the
larger sizes is - it's needle shaped and is hard on the hands in a
throwing body. Great in a hand building body because the needle shapes
interlock and make the clay very strong through all stages.
We did the screen analysis many years ago and yes - hardly any
difference between the 200 and 325 mesh silica. Used to be before the
crushing machines got so efficient.
A dilatometer test is $100 a shot - I have to add - if you want to
understand body making the more dilatometery you have the better.
Without it it's mostly a guessing game.
There is a chapter in Mastering Cone 6 Glazes (chapter 5) which will
be enlightening for anyone wanting to understand what a dilatometer
chart will provide.
If you are interested in writing on the subject so that potters can
understand more about this important tool - I've got a deal for you!
RR
Quoting Dan Parenteau :
> Thanks for the response Ron, a couple follow ups if you're game.
>
> ronroy@ca.inter.net wrote:
>> There is a later article by Peter Sohngen in Studio Potter Volume 28 #1.
>> In essence his research (I did the dilatometery) shows you need at
>> least 10% spar and go easy on micro fine silica (what we usually
>> get in the bag.)
>
> Just re-read that article, which I originally read a few months back
> and didn't quite parse at the time. I think what you're saying is that
> Peter's "Body 12", which has spar but no quartz and comes close to the
> expansion properties of his "Body 7", is an example of a high fire
> stoneware body which has no added silica yet exhibits the glaze fit
> qualities desired. Obviously I've got a few more years of clay body
> formulation experience in my future, but out of curiosity, how much
> does a dilatometer test normally cost?
>
>> Graded silica - like 200M with few fines is not a problem.
>
> From what I've read much of what is sold as 200M is in fact only a
> small percentage 200M and contains a larger percentage of finer size
> particles. I think I'm suffering from being a few degrees of
> separation from the raw materials. Peter's screen analysis of
> available forms of quartz seems like an example of a first step to a
> better understanding of what exactly I'm using.
>
>> Kyanite is a better product for high fire ware.
>
> Hmm, now I have something else to ponder. Kyanite, aka Sillimanite,
> as far as I can tell this might be something used as grog or filler
> to open up a clay body? What mesh size might one recommend for a
> throwing body?
>
> Thanks again, Dan.
>
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