Stephen Grimmer on thu 28 jun 01
Jim,
I believe the RG stands for Refractory Grade, and is pretty spotty
stuff. The HS is much cleaner.
Your body looks like a good starting point. You may wish to seek out a
coarse-grained ball clay for faster casting times, or even switch to
Kaopaque or Velvacast kaolins instead of ball clay for a whiter body.
Steve
--
Stephen Grimmer
Southern Illinois University at Carbondale
> From: Jim Murphy
> Subject: Pyrophyllite For Porcelain Slipcasting Body
>
> Hello all,
>
> I'm new to slipcasting and am going to try my first attempt at mixing
> casting slip based on the following Cone 10 porcelain recipe retrieved from
> the "archives":
>
> Grolleg 25
> Tile 6 15
> Ball Clay 10
> Custer Feldspar 25
> Flint 15
> Pyrophyllite 10
>
> total 100
>
> I plan to bisque at Cone 04 and glaze-fire to Cone 10 oxidation in an
> electric kiln. I'm thinkin' matt/satin glazes rather than glossy.
>
> Any recommendations out there on which type of Pyrophyllite (Pyrax HS, Pyrax
> RG, etc.) may be best for use in this Cone 10 slipcasting body ?
>
> Thanks in advance,
>
> Jim Murphy
Jim Murphy on thu 28 jun 01
Hello all,
I'm new to slipcasting and am going to try my first attempt at mixing
casting slip based on the following Cone 10 porcelain recipe retrieved from
the "archives":
Grolleg 25
Tile 6 15
Ball Clay 10
Custer Feldspar 25
Flint 15
Pyrophyllite 10
total 100
I plan to bisque at Cone 04 and glaze-fire to Cone 10 oxidation in an
electric kiln. I'm thinkin' matt/satin glazes rather than glossy.
Any recommendations out there on which type of Pyrophyllite (Pyrax HS, Pyrax
RG, etc.) may be best for use in this Cone 10 slipcasting body ?
Thanks in advance,
Jim Murphy
Ceramic Design Group on fri 29 jun 01
on 6/29/01 6:10 PM, Jim Murphy at nomocor@MEDIAONE.NET wrote:
> Hi Bill,
>
> You ask, "Why use pyrophylite anyway?" and direct me to the classic "25
> porcelain" casting slip recipe.
>
It also allows to balance out the non-plastic side of the 50:50 ratio of
plastics to non-plastics
>
> a) Maximum use of larger particle size Kaolin to assist in better mold
> drainage (40% total kaolin in the recipe I'm going to try).
Kaolins are the weakest link in a clay system. The strongest links are ball
clays. WIth the proper selection of ball clays, your slip will have the
lower viscosities that you need and cast faster and be much stronger. There
are specific ball clays that are blended for casting. Don't assume that if
you use OM 4, Tenn 5 or Tenn 10 in your plastic throwing body that they will
be the best in your casting formula. They won't. The worst clays for casting
bodies are EPK and OM 4. For the kaolin part, use Grolleg ($$$), or Tile 6
and Kaopaque 20 together, or all with some combination with Pioneer Kaolin.
Use Velvacast liberally. It is also a magic kaolin!! Stay away from EPK in
your casting body.
>
> b) Limit ball clay to minimize shrinkage, warping, cracking, etc.
> I'll be attempting to cast ceramic sculpture so I'm thinking too much ball
> clay in the recipe may yield too many problems. My understanding, though, is
> that a little ball clay can help in regard to ease of trimming, cleaning,
> etc.
Not correct. See above. Ball clays are ESSENTIAL!
>
> c) Limit flint (silica) to decrease likelihood of dunting. Is it true that
> the development of crystobalite during high temperature firing is related
> to available free quartz ? I'm going to be making/firing just a few pieces
> at a time and need to minimize any potential for dunting.
If the flint and spar are in a balanced relationship, then the spar will
take up any free silica during vitrification and decrease the dunting
potential. While this may be difficult to understand, you can replace about
half the flint with Pyrax HS Pyrophyllite and keep the spar the same and get
a very balanced body that is fully vitrified and will not craze your glazes.
If you want some real proof, get a DTA on your clay body.
>
> d) Why Pyrophyllite ? - To act as a filler instead of an additional 10%
> flint (silica) in the recipe. If what I've read since yesterday is true,
> when I posted my original question, then Pyrax HS pyrophyllite is used to
> increase fired strength in sanitaryware and also when used in wall tile may
> decrease crazing due to thermal shock or moisture expansion.
Pyrophyllite is great juju in any ceramic body. We have used it for years in
our plastic bodies for jiggering and RAM pressing, and it has been a
constant in all out casting formulae.
And Bill C is right in that you need to be right on in where your body sits
on the deflocculation curve. Viscosities and specific gravities are very
important and you need to know what they are, how to measure them, and how
to adjust them.
Good Luck
Jonathan
--
Jonathan Kaplan
CERAMIC DESIGN GROUP
PO Box 775112
Steamboat Springs, CO 80577
(970) 879-9139
Jim Murphy on fri 29 jun 01
Stephen,
Thanks for the reply.
> I believe the RG stands for Refractory Grade, and is pretty spotty
> stuff. The HS is much cleaner.
Looks like HS is the winner!
> Your body looks like a good starting point. You may wish to seek out a
> coarse-grained ball clay for faster casting times, or even switch to
> Kaopaque or Velvacast kaolins instead of ball clay for a whiter body.
Sounds like great advice - I'll try mixing small test batches with the
suggested substitutions.
Thanks again,
Jim
>
>> From: Jim Murphy
>> Subject: Pyrophyllite For Porcelain Slipcasting Body
>>
>> Hello all,
>>
>> I'm new to slipcasting and am going to try my first attempt at mixing
>> casting slip based on the following Cone 10 porcelain recipe retrieved from
>> the "archives":
>>
>> Grolleg 25
>> Tile 6 15
>> Ball Clay 10
>> Custer Feldspar 25
>> Flint 15
>> Pyrophyllite 10
>>
>> total 100
>>
>> I plan to bisque at Cone 04 and glaze-fire to Cone 10 oxidation in an
>> electric kiln. I'm thinkin' matt/satin glazes rather than glossy.
>>
>> Any recommendations out there on which type of Pyrophyllite (Pyrax HS, Pyrax
>> RG, etc.) may be best for use in this Cone 10 slipcasting body ?
>>
>> Thanks in advance,
>>
>> Jim Murphy
WHC228@AOL.COM on fri 29 jun 01
Why use pyrophylite anyway? I can see no good reason to use it than to make
your life more complicated than it already is.
The classic recipe for porcelain is
25 kaolin
25 ball clay
25 flint
25 feldspar
There are endless variations of this, however when the smoke clears away they
are close to that.
Knowing how and what to set your specific gravity to, and being able to set
your slip in the correct spot on a defloculation curve is probably the most
important thing to learn. Most production problems usually come back to that.
I have been casting for over twenty years with a slight variation on that
classic recipe. The only change that I have made is to adjust the flint
alumina ratio to help the glaze fit.
Some folks put in a percentage or two of talc to help with thermal shock.
Good luck
Bill
Jim Murphy on fri 29 jun 01
Hi Bill,
You ask, "Why use pyrophylite anyway?" and direct me to the classic "25
porcelain" casting slip recipe.
Great question! I'll try to answer with respect to the "25 porcelain"
recipe.
Basically, I want to start with a balanced Cone 10 casting slip recipe that
allows the following:
a) Maximum use of larger particle size Kaolin to assist in better mold
drainage (40% total kaolin in the recipe I'm going to try).
b) Limit ball clay to minimize shrinkage, warping, cracking, etc.
I'll be attempting to cast ceramic sculpture so I'm thinking too much ball
clay in the recipe may yield too many problems. My understanding, though, is
that a little ball clay can help in regard to ease of trimming, cleaning,
etc.
c) Limit flint (silica) to decrease likelihood of dunting. Is it true that
the development of crystobalite during high temperature firing is related
to available free quartz ? I'm going to be making/firing just a few pieces
at a time and need to minimize any potential for dunting.
d) Why Pyrophyllite ? - To act as a filler instead of an additional 10%
flint (silica) in the recipe. If what I've read since yesterday is true,
when I posted my original question, then Pyrax HS pyrophyllite is used to
increase fired strength in sanitaryware and also when used in wall tile may
decrease crazing due to thermal shock or moisture expansion. These
characteristics may be just the ticket for my slipcast sculpture as well
although pyrophyllite ($0.20/Lb) will cost me 50% more per pound than flint
($0.13/Lb).
I'll try to "fit" my soon to be home-brewed glazes using Ian Currie's grid
method (great book - "Revealing Glazes") along with "Insight" software.
Let the adventure begin !
Thanks for the help,
Jim
Jim Murphy on sat 30 jun 01
Ron,
Thanks for the clarification of dunting when firing porcelain to bisque
temperature. I do plan to bisque to 04.
> The dunting problem is very real when firing porcelain to bisque
> temperatures - all that free silica (quartz) has to go through the
> inversion at 573C - fire to 04 and get the ware - especially plates and
> platters off the shelf with shims and/or cool slowly from 700C down to
> 500C. I alway keep them on the uppermost shelves because they cool slower.
I'm making disks out of 9 parts Alumina Hydrate to 1 part Bentonite. Each
disk will be raised off the shelf by clay wadding (Kaolin & EPK). Each piece
of ware will sit on top of a separate disk. I'm hoping the disks: (a) will
not warp/crack during bisque firing; (b) will not warp/crack during Cone 10
glaze firing; and (c) will be reuseable. I guess I'll find out pretty soon.
Jim Murphy
Jim Murphy on sat 30 jun 01
Jonathon,
Thanks for steering me straight on kaolin & ball clay use:
> Kaolins are the weakest link in a clay system. The strongest links are ball
> clays. WIth the proper selection of ball clays, your slip will have the
> lower viscosities that you need and cast faster and be much stronger. There
> are specific ball clays that are blended for casting. Don't assume that if
> you use OM 4, Tenn 5 or Tenn 10 in your plastic throwing body that they will
> be the best in your casting formula. They won't. The worst clays for casting
> bodies are EPK and OM 4. For the kaolin part, use Grolleg ($$$), or Tile 6
> and Kaopaque 20 together, or all with some combination with Pioneer Kaolin.
> Use Velvacast liberally. It is also a magic kaolin!! Stay away from EPK in
> your casting body.
Pioneer Kaolin and Velvacast are not stocked by my local ceramic supplier.
Based upon the materials I have presently, the Cone 10 casting slip recipe
looks like this:
Grolleg 25
Tile 6 15
C & C Ball Clay (H.C. Spinks) 10
Custer Feldspar 25
Flint (200-mesh silica) 15
Pyrophyllite (Pyrax HS) 10
Total 100
Some have recommended using a coarse-grained ball clay. C & C is advertised
by H. C. Spinks as fine-grained. I think I'll try it since I already bought
a 50 Lb bag.
> And Bill C is right in that you need to be right on in where your body sits
> on the deflocculation curve. Viscosities and specific gravities are very
> important and you need to know what they are, how to measure them, and how
> to adjust them.
I figure I'd buy a plastic graduated cylinder and drill a small hole in the
bottom to serve as a viscosity-measuring device - along with a stop-watch of
course.
I've got an Ohaus triple-beam balance that I'll use to measure S.G. (I'd
like to get this casting slip S.G. to 1.8 if possible).
My biggest challenge right now, I believe, is to determine which
deflocculant(s) to use (Soda Ash & Sodium Silicate combined, Sodium Silicate
alone, Darvan, etc.).
Up until yesterday I was planning on trying to deflocculate using a 0.05%
Soda Ash and 0.15% Sodium Silicate combination. However, based on some of
the feedback I've received on this casting slip topic, I wonder if Soda Ash
is required at all. Perhaps Sodium Silicate alone may do the trick.
I'm open to any deflocculant suggestions.
Best regards,
Jim Murphy
Ron Roy on sat 30 jun 01
I have many dilatometer charts of porcelains - never seen any cristobalite
in any porcelains - too much spar - that makes it imposible for any build
up.
I also noticed some one say there is no quartz - I have never seen no
quartz ina porcelain - even the translucent kind - it is always there but
always less than in a stoneware body.
The dunting problem is very real when firing porcelain to bisque
temperatures - all that free silica (quartz) has to go through the
inversion at 573C - fire to 04 and get the ware - especially plates and
platters off the shelf with shims and/or cool slowly from 700C down to
500C. I alway keep them on the uppermost shelves because they cool slower.
RR
>c) Limit flint (silica) to decrease likelihood of dunting. Is it true that
>the development of crystobalite during high temperature firing is related
>to available free quartz ? I'm going to be making/firing just a few pieces
>at a time and need to minimize any potential for dunting.
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
Jim Murphy on sun 1 jul 01
on 7/1/01 12:02 PM, Ceramic Design Group at jdkaplan@CMN.NET wrote:
> Your ratios of plastic to non-plastic are correct. Velvacast is a very
> coarse grained kaolin made specifically for casting bodies. You can tune the
> casting rate with this material. Get a sample of FC 340 ball clay from Old
> Hickory CLay Co. It is designed specifically for casting, FC= fast cast.
Message received - I'll continue searching for suppliers and save that bag
of C & C Ball Clay for a future project.
> Use Darvan 811, not Darvan 7. Stay away from sodium silicate and soda ash
> defloculation systems as they have a very narrow working range and will beat
> the heck out of your molds. Darvan 811 is a chained polymer, a mand made
> sodium polyacrylate that has a very wide working range
> Trust me, use the Darvan 811 (RT Vanderbilt, in CT or Califormia.)
> Darvan 811 is the same as Spinks 211, by the way.
Very interesting.
Thanks again Jonathon,
Jim Murphy
Ceramic Design Group on sun 1 jul 01
on 6/30/01 10:53 AM, Jim Murphy at nomocor@MEDIAONE.NET wrote:
>
> Pioneer Kaolin and Velvacast are not stocked by my local ceramic supplier.
> Based upon the materials I have presently, the Cone 10 casting slip recipe
> looks like this:
>
> Grolleg 25
> Tile 6 15
> C & C Ball Clay (H.C. Spinks) 10
> Custer Feldspar 25
> Flint (200-mesh silica) 15
> Pyrophyllite (Pyrax HS) 10
>
> Total 100
>
> Some have recommended using a coarse-grained ball clay. C & C is advertised
> by H. C. Spinks as fine-grained. I think I'll try it since I already bought
> a 50 Lb bag.
Your ratios of plastic to non-plastic are correct. Velvacast is a very
coarse grained kaolin made specifically for casting bodies. You can tune the
casting rate with this material. Get a sample of FC 340 ball clay from Old
Hickory CLay Co. It is designed specifically for casting, FC= fast cast.
Talk to Russ Fish at Old Hickory. He can really open your eyes to the
differences in ball clays.
>
>
>> And Bill C is right in that you need to be right on in where your body sits
>> on the deflocculation curve. Viscosities and specific gravities are very
>> important and you need to know what they are, how to measure them, and how
>> to adjust them.
>
> I figure I'd buy a plastic graduated cylinder and drill a small hole in the
> bottom to serve as a viscosity-measuring device - along with a stop-watch of
> course.
Well, that should work but it really becomes a reference only to you and
within your studio. A common viscosimeter is a # 2 Zahn cup available from
Gardco (Paul Gardner Co) in Pompano Beach, Florida) and is a standard. So
lets say you are having some difficulty with your slip and want to use a
consultant. If that consultant has a #2 Zahn cup as well as you, then the
vocabulary is the same. YOu caould invest lots of money in a Brookfield
machine, but a 3@ Zahn cup will be quite accurate for you.
>
> I've got an Ohaus triple-beam balance that I'll use to measure S.G. (I'd
> like to get this casting slip S.G. to 1.8 if possible).
You may be better of between 1.76-1.77, but only your casting casting
experience will show you.
>
> My biggest challenge right now, I believe, is to determine which
> deflocculant(s) to use (Soda Ash & Sodium Silicate combined, Sodium Silicate
> alone, Darvan, etc.).
Use Darvan 811, not Darvan 7. Stay away from sodium silicate and soda ash
defloculation systems as they have a very narrow working range and will beat
the heck out of your molds. Darvan 811 is a chained polymer, a mand made
sodium polyacrylate that has a very wide working range
>
> Up until yesterday I was planning on trying to deflocculate using a 0.05%
> Soda Ash and 0.15% Sodium Silicate combination. However, based on some of
> the feedback I've received on this casting slip topic, I wonder if Soda Ash
> is required at all. Perhaps Sodium Silicate alone may do the trick.
Careful with that stuff. It is a very powerful deflocculant and you can
easily make your slip thixotropic without too much work. Trust me, use the
Darvan 811 (RT Vanderbilt, in CT or Califormia.)
Darvan 811 is the same as Spinks 211, by the way.
Good Luck
Jonathan
--
Jonathan Kaplan
CERAMIC DESIGN GROUP
PO Box 775112
Steamboat Springs, CO 80577
(970) 879-9139
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