Daniel Semler on fri 18 aug 06
Hi Marci,
It can be estimated by calculation and it can be measured by
dilatometry. The estimates are made based on % content of each oxide
times its coefficient of expansion, and these are then totalled. Of
course, there have been a number of sets of tabels of expansion
coefficients produced and of course they differ. Glaze calculation
programs will generate estimates on this basis using one table or
another. There is a good paper on this on Dave Hewitt's web site at
http://www.dhpot.demon.co.uk/ under Calculating Crazing.
Measurement requires access to a dilatometer and the use of a
sample of the glaze fired as a small bar or rod.
This all rather presumes that you have access to expansion info on
the glass you are trying to mate it with. This of course leads to the
question, what are you trying to do exactly ?
Thx
D
marci Boskie's Mama =^..^= on fri 18 aug 06
Does anyone have an idea of how to figure out the Coefficient of Expansion
of a glaze? I want to do some work with glazes ( mostly clear) in
relation to glass and they would have to be compatible...
Marci Blattenberger Boskie's Mama =^..^=
http://www.marciblattenberger.com
marci@ppio.com
Porcelain Painters International Online http://www.ppio.com
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David Hewitt on sat 19 aug 06
Marci,
May I suggest that you go to my web site and under 'Pottery Techniques'
click on 'Calculating Crazing'
http://www.dhpot.demon.co.uk
I hope this will help you, but if you have any further questions, please
get back to me.
David
In message , marci Boskie's Mama =^..^= writes
>Does anyone have an idea of how to figure out the Coefficient of Expansion
>of a glaze? I want to do some work with glazes ( mostly clear) in
>relation to glass and they would have to be compatible...
>
>Marci Blattenberger Boskie's Mama =^..^=
> http://www.marciblattenberger.com
> marci@ppio.com
>Porcelain Painters International Online http://www.ppio.com
>
>
>--
>No virus found in this outgoing message.
>Checked by AVG Anti-Virus.
>Version: 7.1.405 / Virus Database: 268.11.2/422 - Release Date: 8/17/2006
--
David Hewitt
Web:- http://www.dhpot.demon.co.uk
Ron Roy on mon 21 aug 06
Hi Marci,
I have had good results with calculating shiny glazes - I have compared the
results with the actual measurements from a dilatometer.
The trick in this case is to try to get the recipe or formula for the glass
so you can compare.
I can also measure glazes and glass in my dilatometer - at $100 per sample
- again - I would need a sample of the glass in rod form to measure it as
well.
I would try the calculation method first - providing you can get the info
on the glass - or have a sample analysed.
RR
>Does anyone have an idea of how to figure out the Coefficient of Expansion
>of a glaze? I want to do some work with glazes ( mostly clear) in
>relation to glass and they would have to be compatible...
>
>Marci Blattenberger Boskie's Mama =^..^=
> http://www.marciblattenberger.com
> marci@ppio.com
>Porcelain Painters International Online http://www.ppio.com
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
David Beumee on wed 23 aug 06
I've always wanted to use a porcelain body of calculated COE of just slightly higher contraction than the covering clear glaze, putting the glaze in slight compression, creating a particularly strong overall result. How would a person create a clear glaze in rod form?
David Beumee
-------------- Original message ----------------------
From: Ron Roy
> Hi Marci,
>
> I have had good results with calculating shiny glazes - I have compared the
> results with the actual measurements from a dilatometer.
>
> The trick in this case is to try to get the recipe or formula for the glass
> so you can compare.
>
> I can also measure glazes and glass in my dilatometer - at $100 per sample
> - again - I would need a sample of the glass in rod form to measure it as
> well.
>
> I would try the calculation method first - providing you can get the info
> on the glass - or have a sample analysed.
>
> RR
>
>
> >Does anyone have an idea of how to figure out the Coefficient of Expansion
> >of a glaze? I want to do some work with glazes ( mostly clear) in
> >relation to glass and they would have to be compatible...
> >
> >Marci Blattenberger Boskie's Mama =^..^=
> > http://www.marciblattenberger.com
> > marci@ppio.com
> >Porcelain Painters International Online http://www.ppio.com
>
> Ron Roy
> RR#4
> 15084 Little Lake Road
> Brighton, Ontario
> Canada
> K0K 1H0
>
> ______________________________________________________________________________
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Ron Roy on tue 29 aug 06
Hi David,
I think you know it - but you cannot calculate the expansion of a clay body
- silica in it's many forms has too much influence to start with and you
never know how much of what kind is in a body after firing. Besides - Only
calculation of a shiny glaze is acurate.
Here are my instructions for preparing samples for my dilatometer - let me
know if you have any questions.
I can send you a picture of a "boat" if you want - RR
Preparing samples for my dilatometer.
Clay:
I need two fired samples (your normal glaze firing cycle) 2 inches long and
about 3/8 inch diameter - NO GLAZE. Make them longer - 3 to 3.5 inches long
and I will cut to length.
The main things to keep in mind - they need to be smooth and straight. I
recommend rolling a coil with something flat - I use a piece of stiff but
flexible plastic - make sure the coil is even and smooth no bumps - no
taper - dry in a way that allows no warping - slowly and out of any drafts
- under a piece of paper.
I make mine with a series of dots impressed into the clay at one e3nd of
the sample with a pencil to identify what clay - don't forget to roll again
to take out any bumps caused by the marking. Do not write on the sample as
that may affect melting and give a false reading.
Don't use anything to write on the clay - not even a pencil - it will
affect the clay.
Fire with a cone beside them and include the cone or drawing with the bars.
Fire to glaze fire temperature and ship to me at:
RR #4 - 15084 Little Lake Road, Brighton, Ontario. KOK 1H0.
If sending from outside Canada mark the customs declaration - SAMPLE - no value.
Glaze:
Take a piece of soft fire brick (that will withstand your glaze firing) and
file out a groove about 1/2 inch wide and 3/4 inch deep - a little wider at
the top. Make some stoppers for the each end out of fire brick - leaving
about 3.5 inches in between for glaze. Wet the boat a little and coat all
the inside area with alumina hydrate mixed with vinegar and a little
bentonite to help keep it suspended. Pour in your glaze - wait for it to
settle and top up until full. Fire in a normal firing, lift the sample out,
and send to me - I will grind off all the excess material and cut to size.
Remember - I need to trim both ends and cut to 2 inches exactly so I need
the sample to be about 3 to 3.5 inches.
>I've always wanted to use a porcelain body of calculated COE of just
>slightly higher contraction than the covering clear glaze, putting the
>glaze in slight compression, creating a particularly strong overall
>result. How would a person create a clear glaze in rod form?
>
>David Beumee
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
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