John Post on sun 22 feb 98
The question that I have for Ron is about the expansion of the glazes
listed below. A while back you told me that the expansion for the PMSP-4
glaze was a little low. You sent me a revised version which had a slightly
higher expansion. I then looked at Tony Hansen's 5-20 glaze and found it
to be pretty close to my PMSP-4. What range do you think the expansion
should be in for a cone 6 oxidation glaze?
PMSP-4 Expansion coefficient: 68.0 x 10e-7 per degree C
Ron Roy's version of PMSP-4 Expansion coefficient: 71.1 x 10e-7 per degree C
Tony Hansen's 5-20's glaze Expansion coefficient: 69.2 x 10e-7 per degree C
In terms of my experience firing these glazes, I have found the PMSP to be
water clear. Your revision to be mostly clear with bubbles only in areas of
relief where the glaze has pooled. The 5-20's glaze for me was cloudy.
I'm wondering if Ron Wright is getting more bubbles because he is trying to
get a THICK clear? My clear gets a 4 second dip and I can't find any
bubbles in it under a 1.5x magnifying glass.
For anyone following this thread, all of the above glazes are given below.
All are cone 6 oxidation. My firing takes about 8-9 hours to bend a large
cone 6 and then I soak the kiln for another half hour to hour until cone 7
is at 2 o'clock. I then turn all of the switches to medium for 3 hours
before shutting it off.
>I have since tested 2 other glazes that are nice and clear when thin but
>have billions and billions of tiny bubbles (my apologies to Carl Sagen)
>where they are applied thick. The glazes just look slightly opaque or
>whitish but under a microscope you can see the bubbles. Ron Roys version
>is the bubbliest of all, but is great with oxides. Tried firing to cone
>8 and soaking, still have bubbles. I'm trying to get a thick clear for a
>decorating technique I'm working on.
>
>I have just tested a batch of Post's PMSP-4 clear glaze from the
>>GlazeBase at cone 6. It came out cloudy, and when I whipped out my new
>>field microscope (another great idea from the group) I found that it was
>>full of tiny bubbles. The comments on this glaze states that it is
>>transparent with no bubbles. How did I screw this up?
>>
>>Post's PSMP-4
>>cone 6-7-8
>>clear gloss
>>
>>Ferro Frit 3134 40.13
>>Wollastonite 15.73
>>EPK 18.06
>>Flint 19.66
>
The correct formula for Post's PMSP-4 is below. The one posted on the
database (and above) is incorrect.
++++++++++++++++++++++++
+++ PMSP 4 Base +++
+++++++++++++++++++++++
Range: 6-8
Firing type: Oxidation
Glaze type: Stoneware
Surface: Gloss
Date: 11/12/96
Frit 3134 2032 25.4%
Nepheline syenite 640 8 %
Wollastonite 1568 19.6%
EPK 1800 22.5% Hazard!
Flint 1960 24.5% Hazard!
-------- ------
8000 100 %
===========================
Chemical Analysis
===========================
Na2O 0.18 Al2O3 0.35 SiO2 3.26
K2O 0.01 B2O3 0.27
MgO 0.02
CaO 0.79
Alumina:Silica ratio is 1.00 : 9.41
Neutral:Acid ratio is 1.00 : 5.30
Alkali:Neutral:Acid ratio is 1.00 : 0.62 : 3.26
Expansion coefficient: 68.0 x 10e-7 per degree C
Oxides causing abnormal expansion effects: B2O3
++++++++++++++++++++++++++
+++ Ron Roy PMSP-4 +++
++++++++++++++++++++++++++
Date: 01/20/98
Frit 3134 84 21 %
Nepheline syenite 76 19 %
Wollastonite 80 20 %
EPK 64 16 % Hazard!
Flint 96 24 % Hazard!
-------- ------
400 100 %
===========================
Chemical Analysis
===========================
Na2O 0.21 Al2O3 0.34 SiO2 3.28
K2O 0.03 B2O3 0.22
MgO 0.02
CaO 0.74
Alumina:Silica ratio is 1.00 : 9.61
Neutral:Acid ratio is 1.00 : 5.85
Alkali:Neutral:Acid ratio is 1.00 : 0.56 : 3.28
Expansion coefficient: 71.1 x 10e-7 per degree C
Oxides causing abnormal expansion effects: B2O3
++++++++++++++++++++++++++++++
+++ 5-20's Tony Hansen +++
++++++++++++++++++++++++++++++
Date: 02/18/98
EPK 80 20 % Hazard!
Custer feldspar 80 20 %
Wollastonite 80 20 %
Frit 3134 80 20 %
Flint 80 20 % Hazard!
-------- ------
400 100 %
===========================
Chemical Analysis
===========================
Na2O 0.14 Al2O3 0.38 SiO2 3.44
K2O 0.07 B2O3 0.22
MgO 0.02
CaO 0.76
Alumina:Silica ratio is 1.00 : 9.08
Neutral:Acid ratio is 1.00 : 5.75
Alkali:Neutral:Acid ratio is 1.00 : 0.60 : 3.44
Expansion coefficient: 69.2 x 10e-7 per degree C
Oxides causing abnormal expansion effects: B2O3
John Post
jp6mchp@moa.net
Sterling Heights, Michigan
Ron Roy on tue 24 feb 98
Hi John,
I'm behind as usual and I see I have some explaining to do so bear with me.
I have included a printout of two glazes - yours and mine in case anyone is
wondering what I am talking about.
First - I am using a different expansion scale than everyone else - doesn't
matter - we still agree about which is higher and lower - and these numbers
are confirmed by actual dilatometer measurements. It also turns out that
mine are closer to the truth than the standard way of expressing them.
That's another story - later for that.
My expansion # for my glaze using my scale is 447.2 - using the Insight
numbers it's 7.08 and yours is 71.1
My expansion # for your glaze using my scale is 408.62 - using Insight
numbers it's 6.81 and yours is 68.0
So why do I think yours are too low. Well it depends on how you are firing
- you are developing a good clay/glaze interface - the glaze is bonding
well with the body - so it is working OK.
Once upon a time I was working on glazes for a company down south and they
were getting fit problems unless the glazes I sent were between 150 and
140. I didn't realize they were fast firing - the glaze was not forming a
decent bond with the clay and even small differences were showing up. So
now I tend to keep cone 6 glazes within that range.
That company stiffed me for hundreds of dollars by the way - if you ever
have to deal with DK Clays in Dayton NC - get the money up front.
I find myself trying to imagine at what speed the ware is being fired at
when I am working on a glaze - so I design for the worst kind of scenarios
- fast firing.
I have also come to the conclusion that fitting glazes at cone 6 is much
more predictable than at higher temperatures - and lower ones as well. The
type of clay the glaze is on seems to be less critical at cone 6 -
especially if there is boron in the glaze.
So the answer to your question "what range do you think the expansion
should be for a cone 6 glaze?" is - on your scale - high 70.1 - low 70.0
approx.
Tony's glaze is higher than yours - 435.85 my scale 69.5 yours.
Of course all this is academic in the end - the real test is - can you make
it crack by pouring boiling water in it while it's frozen?
The way you are firing and glazing I think there really is no problem - I
would like you to put a heavier coat of your glaze just on the inside of a
thin walled cylinder and test it for fit - if for no other reason than to
change my mind on this.
>----------------------------Original message----------------------------
>The question that I have for Ron is about the expansion of the glazes
>listed below. A while back you told me that the expansion for the PMSP-4
>glaze was a little low. You sent me a revised version which had a slightly
>higher expansion. I then looked at Tony Hansen's 5-20 glaze and found it
>to be pretty close to my PMSP-4. What range do you think the expansion
>should be in for a cone 6 oxidation glaze?
Ron's
-----------------
F3134............... 21.00 21.00%
NEPH SY............. 19.00 19.00%
WOLAST.............. 20.00 20.00%
EPK................. 16.00 16.00%
SILICA.............. 24.00 24.00%
----------
100.00
FORMULA & ANALYSIS
------------------
*CaO........ .60 13.21%
MnO2....... .00 .01%
*MgO........ .02 .35%
*K2O........ .03 .97%
*Na2O....... .17 4.21%
Fe2O3...... .00 .15%
TIO2....... .00 .05%
*B2O3....... .18 5.00%
AL2O3...... .28 11.14%
SiO2....... 2.75 64.92%
P2O5....... .00 .02%
COST/KG 1.51
RATIO 9.91
EXPAN 447.20
WEIGHT 253.87
John's
-----------------
F3134............... 25.40 25.40%
NEPH SY............. 8.00 8.00%
WOLAST.............. 19.60 19.60%
EPK................. 22.50 22.50%
SILICA.............. 24.50 24.50%
----------
100.00
FORMULA & ANALYSIS
------------------
*CaO........ .61 14.00%
MnO2....... .00 .01%
*MgO........ .02 .34%
*K2O........ .01 .48%
*Na2O....... .14 3.60%
Fe2O3...... .00 .19%
TIO2....... .00 .07%
*B2O3....... .21 6.10%
AL2O3...... .27 11.10%
SiO2....... 2.61 64.10%
P2O5....... .00 .03%
COST/KG 1.65
RATIO 9.82
EXPAN 408.62
WEIGHT 244.73
Ron Roy
93 Pegasus trail
Scarborough Otario
Canada M1G 3N8
Phone: 416-439-2621
Fax: 416-438-7849
Web page: Home page http://digitalfire.com/education/people/ronroy.htm
John Post on wed 25 feb 98
>So the answer to your question "what range do you think the expansion
>should be for a cone 6 glaze?" is - on your scale - high 70.1 - low 70.0
>approx.
>
Hi Ron,
Is this range correct? 70.0 - 70.1 must be a typo. I was expecting
something like 70.0 - 80.0. This is the range that most of my glazes are
in, with most in the mid 70's.
John Post
jp6mchp@moa.net
Sterling Heights, Michigan
Ron Roy on thu 26 feb 98
Hi John,
OK - there are two aspects to answer here. First of all you are probably
working with one clay and have a much wider set of parameters than I have
to work with. Once I get over 70.4 on your scale (450 on mine) some glazes
will start to craze on some porcelains - I have to deal with potters who
are using more than one body most of the time. That means I find myself
trying to develop parameters that will fit as many situations as possible.
Consequently the range I work with will have to be more narrow than yours.
I should have qualified my answer - I thought you were asking me what my
parameters were - I should have added - you will be able to ascertain your
own by testing on the bodies you use.
I made up two hypothetical glazes - #1 has a calculated expansion of 450.53
on my scale. #2 is lower at 440.01 - I try to keep the cone 6 glazes within
that range.
Expansion of 450.53 (high limit) works out to 70.4
Expansion of 440.01 (low limit) works out to 70.6 whoops - that's supposed
to be lower - not higher. Seems we are not able to compare our results
using the different base expansion numbers. I have checked the Insight
numbers and notice some differences in proportion - The Insight numbers
have SiO2 and B2O3 as having the same value. I don't know what to do now -
I am including the numbers I use so you can come to your own conclusions.
Oxides - Expan
BaO -14.00
CaO - 16.30
MnO2 - 5.70
Li2O - 7.45
MgO - 4.50
K2O - 39.00
Na2O - 41.60
ZnO - 7.00
Fe2O3 - 10.40
TiO2 - 10.60
B2O3 - -6.53 (yes that's a minus)
Al2O3 - 1.40
SiO2 - 0.50
PbO -10.60
P2O5 - 7.45
SnO2 - 3.65
ZrO2 - 2.30
SrO - 13.50
The other question re you were expecting the high limit to be more like
78.0 - that's too high I think. Stoneware clays are easier to fit glazes to
- mainly because there is usually some free quartz in the body to help put
or keep the glaze under compression - in porcelains there is usually not as
much - if it's vitrified. I assume from your "safe range" that you are
using stoneware clay - is that correct?
Now I am wondering what conclusion others have come to. Do any of you have
target calculated expansion rates for your glazes? - does anyone use
different sets for different clays? Anyone willing to do some testing on
this.
>----------------------------Original message----------------------------
>>So the answer to your question "what range do you think the expansion
>>should be for a cone 6 glaze?" is - on your scale - high 70.1 - low 70.0
>>approx.
>>
>
>Hi Ron,
>
>Is this range correct? 70.0 - 70.1 must be a typo. I was expecting
>something like 70.0 - 80.0. This is the range that most of my glazes are
>in, with most in the mid 70's.
>
>
>John Post
>jp6mchp@moa.net
>Sterling Heights, Michigan
Ron Roy
93 Pegasus trail
Scarborough Otario
Canada M1G 3N8
Phone: 416-439-2621
Fax: 416-438-7849
Web page: Home page http://digitalfire.com/education/people/ronroy.htm
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