Ron Roy on sat 1 nov 97
Two comments - well three - This glaze looks like it may have the right
expansion for many clays. It is oversupplied with Boron so it may be
subject to leaching for a cone 6 glaze.
Am I wrong in asserting that Plastic Vitrox is not a clay but more like a
low melting feldspar? The analysis certainly does not resemble any other
clays I have seen.
>----------------------------Original message----------------------------
>I have used the following glaze off and on for the last year and fire in the
>cone 5 to 6 range. It is a hard, clear, high gloss glaze. If you have access
>to Plastic Vitrox Clay it might be worth a try. This is from an old issue of
>Ceramics Monthly.
>
>Wide Range PVC Base. cone 3 to 8
>Plactic Vitrox Clay 50
>Gerstley Borate 50
>additions:
> Zircopax 5
> Rutile 5
Ron Roy
93 Pegasus Trail
Scarborough,Canada
M1G 3N8
Evenings, call 416 439 2621
Fax, 416 438 7849
Studio: 416-752-7862.
Email ronroy@astral.magic.ca
Home page http://digitalfire.com/education/people/ronroy.htm
DONPREY on sun 2 nov 97
Ron
I believe you are correct about Plastic Vitrox being more like a feldspar.
However, it has always been referred to as a clay in the literature when I run
across it.....except for a Studio Potter issue on porcelain bodies awhile back
where it was recognized as a feldspar-like material.
Don Prey in Oregon
David Hendley on mon 3 nov 97
At 06:01 PM 11/1/97 EST,
Ron Roy wrote:
>Am I wrong in asserting that Plastic Vitrox is not a clay but more like a
>low melting feldspar? The analysis certainly does not resemble any other
>clays I have seen.
>
Ron, I was wondering the same thing a few years ago,
so I made some 100% plastic vitrox clay.
In my opinion it IS clay, because
I could thow a cup with it.
If memory serves, it survived a ^10 firing
but cracked in 2 on cooling.
David Hendley
Maydelle, Texas
See David Hendley's Pottery Page at
http://www.sosis.com/hendley/david/
Tony Hansen on tue 4 nov 97
MATERIAL: PV CLAY
DESCRIPTION: PLASTIC VITROX, PLASTIC FELDSPAR
DATE: 09/05/97
SUPPLIER: BFM MINERALS
COST: 5.28 per 50BG
RAW WEIGHT: 803.15
ANALYSIS & UNITY FORMULA
========================
CaO....... 1.00% 0.14
K2O....... 5.00% 0.43
MgO....... 0.50% 0.10
Na2O...... 0.90% 0.12
TiO2...... 0.10% 0.01
Al2O3..... 12.70% [ 1.00]
SiO2...... 76.50% 10.22
Fe2O3..... 0.50% 0.03
LOI....... 2.80%
DETAIL NOTES
------------
It is a feldspathic clay semi-abrasive mineral consisting of clay,
mica,
feldspar and silica (Moh hardness of 5). It is a product of the
hydrothermal alteration of intrusive rhyolite and is mined from a
substantial deposit in the Mojave Desert of California. In a ceramic
casting slip or plastic clay body, PV Clay has the unique capability
of
promoting plasticity from the clay portion, fluxing action from the
feldspar portion, and low shrinkage and stability from the
non-plastic
quartz portion.
Its relatively high potash and soda content give P. V. Clay a lower
PCE
than most kaolins and ball clays (18 vs. 26-35), and thus it has
become
widely used in the ceramic industry as a low temperature flux for
artware
and tile bodies. Its formula is quite similar to Cornwall Stone. It
has the
unique ability to promote plasticity, fluxing and stability all from
the
same material.
Its loss on ignition (approx 3% vs 10-15 for kaolins and ball clays)
and
its high silica content tend to impart low shrinkage, good density,
and
excellent hardness at low firing temperatures in the range
1900-2100F.
It has an ideal combination of feldspathic silicates and kaolinites
that
permit low temperature firing in high talc bodies with exceptional
resistance to glaze crazing and dunting during cooling.
It fires white to impart outstanding casting properties to ceramic
casting
bodies and floor & wall tile bodies.
P.V. Clay is also used as a filler in rubber products, as a mild
abrasive
in polishes and cleansers, and as an extender for coatings,
compounds, and
other industrial products.
PV Clay is used in the "California Artware Body" as follows:
California Talc 3 parts
PV Clay 1 part
Ball Clay Blend 2 parts
This produces a casting body which casts quickly, has good dry
strength, a
light color and long firing range and resists crazing very well.
Firing properties are strongly influenced by the particle size (the
finer
the grade, the better vitrification achieved). P. V. clay can reach
vitrification at cone 8, and is even used in glazes with success. A
simple
50:50 mix of P. V. Clay and Gerstley Borate is used widely as a
transparent
glaze at cone 5-7.
The manufacturer claims that the material is maintained to constant
uniformity chemically and physically by careful mining, close
particle size
control and cleanliness in milling and rigid laboratory control.
Particle Size Distribution
(typical Sedigraph Method)
40 91.0 (below 40 microns)
30 77.5
20 67.0
15 61.5
10 56.0
7.5 51.0
5 43.0
4 40.0
3 35.0
2 31.0
1 23.5
Mineralogical Analysis:
----------------------
Flint 46%
Feldspar 34%
Kaolinite 24%
Sulphur .03
LOI 2.3%
Specific Gravity 2.65
pH 9.2
Dry Brightness 82
Fired Brightness 80
Apparent Density
(lbs./ft3) 27
Tapped Density 66
Unfired Physical Properties:
Rate of Cast, Thickness 15 min
(specific gravity 1.5) 1.21 cm 1.27 cm 1.83 cm
Percent water of plasticity: 28 29 32
Percent dry shrinkage 4.2 4.4 4.8
Cone 03 Cone 5 Cone
8
---------------------- --------------------
--------------------
LOI 1.2 2.4 2.9 1.6 2.7 3.0 2.2
2.7
3.3
Absorption: 19.5 18.8 20.6 11.7 6.4 .6 6.0
..2
.1
Fire Shr: .5 1.0 1.0 5.2 8.1 10.7 8.0
9.9
10.1
MOR: 1051 1202 1807 3357 4482 6717 4812
6257
6900
Color light buff Brown Gray lt
med med
grey
gray gray
PCE Cone 18
Melting Point: 2700F
--
-------
T o n y H a n s e n thansen@digitalfire.com
Get INSIGHT, Magic of Fire at http://digitalfire.com
Louis Katz on tue 4 nov 97
=3C/NOFILL=3E
------------------
Plastic Vitrox Clay (PVC), gets a lot of use because it serves the
functions of flux and plasticizer. But it makes very flabby bodies. I
have seen it used at cone 6, 10 and 04. It is an ingredient in an 04
casting bodie that I saw in a clay company catalog somewhere, it might
be Georgies Clay. I have mixed some bodies with PVC but I avoid it now
like the plague. The bodies seem thixotropic and are difficult to
manage IMHO.
When I came down here we had a lot of PVC so I tried making some
glazes out of it. The glazes all had crawling problems, but that was
before I switched to distilled water.
Louis
Ron Roy on sat 8 nov 97
Thanks David - I see I should have said a higher melting feldspar - I
suspect you would have trouble throwing anything much bigger than a cup -
is that true?
Thanks to all who posted information on this material.
>Ron, I was wondering the same thing a few years ago,
>so I made some 100% plastic vitrox clay.
>In my opinion it IS clay, because
>I could thow a cup with it.
>If memory serves, it survived a ^10 firing
>but cracked in 2 on cooling.
>
>David Hendley
Ron Roy
93 Pegasus Trail
Scarborough,Canada
M1G 3N8
Evenings, call 416 439 2621
Fax, 416 438 7849
Studio: 416-752-7862.
Email ronroy@astral.magic.ca
Home page http://digitalfire.com/education/people/ronroy.htm
Ron Roy on sat 8 nov 97
Thanks Louis,
>----------------------------Original message----------------------------
> ------------------ Plastic Vitrox Clay (PVC), gets a lot of use because
>it serves the functions of flux and plasticizer. But it makes very flabby
>bodies. I have seen it used at cone 6, 10 and 04. It is an ingredient in
>an 04 casting bodie that I saw in a clay company catalog somewhere, it
>might be Georgies Clay. I have mixed some bodies with PVC but I avoid it
>now like the plague. The bodies seem thixotropic and are difficult to
>manage IMHO.
>When I came down here we had a lot of PVC so I tried making some glazes
>out of it. The glazes all had crawling problems, but that was before I
>switched to distilled water.
>Louis
Ron Roy
93 Pegasus Trail
Scarborough,Canada
M1G 3N8
Evenings, call 416 439 2621
Fax, 416 438 7849
Studio: 416-752-7862.
Email ronroy@astral.magic.ca
Home page http://digitalfire.com/education/people/ronroy.htm
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