Karen Shapiro on sat 30 oct 99
Hi Clayarters,
OK, I've searched through the archives twice now looking for the answer to
this question and can't find the posts on this subject. I remember seeing
them but unfortunately didn't print them out.
What do I add to a glaze to make it matte? I do lowfire - raku work.
Also, anyone have a lowfire clear matte glaze? Not satin, but matte.
Appreciate any help,
Karen in Sonoma
ababy sharon on sun 31 oct 99
Hallo Karen
The best way is to buy a software and use it,but you can do it also by:
ADDING silica(or decrease it) or adding alumina. I like the Alumina hydrate
as it gives softer look to the glaze
Ababi
----- Original Message -----
From: Karen Shapiro
To:
Sent: Saturday, October 30, 1999 06:45
Subject: how to "matte" a glaze
> ----------------------------Original message----------------------------
> Hi Clayarters,
>
> OK, I've searched through the archives twice now looking for the answer to
> this question and can't find the posts on this subject. I remember seeing
> them but unfortunately didn't print them out.
> What do I add to a glaze to make it matte? I do lowfire - raku work.
>
> Also, anyone have a lowfire clear matte glaze? Not satin, but matte.
>
> Appreciate any help,
>
> Karen in Sonoma
>
Jim Brooks on sun 31 oct 99
Karen.. a while back there was an article in CM that said you could matt any
glaze with zirconium spinels. The idea being the the melting point of
zirconium was so high that it didn't enter into the glaze reaction.
Therefore, it would matt the glaze without affecting the color. Im sure
that there is someone out who can help with this and confirm or deny it..
Anyway..it would be worth a try..
Vince Pitelka on tue 2 nov 99
>The best way is to buy a software and use it,but you can do it also by:
>ADDING silica(or decrease it) or adding alumina. I like the Alumina hydrate
>as it gives softer look to the glaze
The glaze gurus will no doubt comment further on this, but I would be very
wary of matting a glaze by adding alumina. It essentially just produces an
under-fired glaze, which is less resistant to abrasion and chemicals. In
other words, it is more likely to release compounds into your food.
- Vince
Vince Pitelka
Home - vpitelka@DeKalb.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
NakedClay@aol.com on wed 3 nov 99
Hi Karen!
There have already been several good answers to your question. I have this to
add:
If you underfire a glaze, most often it will be a matte surface. In other
words, fire a cone 10 glaze to cone 6 or 8. Be cautioned, that underfiring a
glaze more than four cones will probably produce wares that look unfinished
or like one made a drastic error!
Like all else in glazing clay wares, it's important to experiment first,
before committing a batch of good wares to a questionable glaze.
Best wishes!
Milton NakedClay@AOL.COM
Jonathan Kaplan on wed 3 nov 99
Sure its possible to matte a glaze by adding alumina, and it is also
possible to change a glaze to be anything by randomly adding materials
without any regard or knowledge of what will happen. This uneducated and
really unsafe practice is perhaps only good to see what will happen, and
nothing else. The glass that may be produced will be quite imperfect.
So please, buy what ever software you need. Spend the money and start to
learn about ceramic materials and what happens when they are heated and
form a glaze. The results will be well worth your efforts of testing, not
to mention that your glazes will be safer.
Jonathan
Jonathan Kaplan
Ceramic Design Group
PO Box 775112
Steamboat Springs CO 80477
voice and fax 970 879-9139
jonathan@csn,net
http://www.sni.net/ceramicdesigin
Vince Pitelka on thu 4 nov 99
>If you underfire a glaze, most often it will be a matte surface. In other
>words, fire a cone 10 glaze to cone 6 or 8. Be cautioned, that underfiring a
>glaze more than four cones will probably produce wares that look unfinished
>or like one made a drastic error!
I missed out on the first part of this thread, so I do not know if the
subject of discussion is utilitarian wares or non-utilitiarian work. If it
is the former, this is bad advice. One should never settle for an
under-fired glaze on a utilitarian pot. As I mentioned in an earlier post,
such a glaze is less resistant to abrasion and chemical attack, and more
likely to release compounds into your food.
Best wishes -
- Vince
Vince Pitelka
Home - vpitelka@DeKalb.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Ron Roy on thu 4 nov 99
There are many ways to matte a glaze - the suggestion to add alumina
does lower the silica/alumina ratio and if it gets below 5.00 (5 SiO2
to 1 Al2O3) then chances are - (if you are cooling slow enough) your
glaze will recrystallize.
It is probable though that just adding alumina will make the glaze
underfired - and that is not a true alumina matte.
If you were starting with a glaze that was already short of silica
and over fluxed then it might be possible to get a proper clay matte
by just adding alumina. This would be the hard way because alumina by
itself is very hard to melt. Materials that are already combined are
easier to melt.
For instance most Kaolins (calcined or raw) have a ratio of about
2.00 - a much more efficient way of getting a clay matte is to lower
the silica and raise the clay - preferably in the form of kaolin.
Ball clays - because they have much more silica than Kaolins are not
recommended - in fact some have ratios over 5.00 so adding them would
do the opposite.
So why be concerned with how hard it is to melt a glaze you ask?
Aside from the obvious costs of firing higher - if your glazes have
less flux (read more alumina and silica) then your glazes will be
more durable. So why is wolastonite a better source of Calcium oxide
than Whiting? Because in wolastonite the CaO and the SiO2 is already
combined and will melt faster.
Same for kaolin and alumina - RR
>----------------------------Original message----------------------------
> >The best way is to buy a software and use it,but you can do it also by:
> >ADDING silica(or decrease it) or adding alumina. I like the Alumina hydrate
> >as it gives softer look to the glaze
>
>The glaze gurus will no doubt comment further on this, but I would be very
>wary of matting a glaze by adding alumina. It essentially just produces an
>under-fired glaze, which is less resistant to abrasion and chemicals. In
>other words, it is more likely to release compounds into your food.
Ron Roy
93 Pegasus Trail,
Scarborough, Ontario
Canada. M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
Tony Hansen on sat 6 nov 99
A side point to emphasize that matte glazes can be matte for a variety of
reasons. Understanding the reason why your glaze is matte is a secret
to controling and adjusting it.
Consider: A glaze recipe might fire matte because:
-It has a high alumina and low silica ratio and the alumina stiffens the
melt so that the microsurface is rippled.
-It is not being fired high enough to melt properly.
-It is covered with a fine mesh of crystals that grow during cooling.
Knowing this will give you direction if you need to adjust. For example,
to make an underfired matte glossier you add feldspar, to make an
alumina matte glossier you add silica, to make a crystal matte glossier
you cool more quickly or increase kaolin to stiffen the melt and impede
crystal growth. Three different mechanism, three completely different
approaches to solve the same problem.
--
T o n y H a n s e n thansen@digitalfire.com
Don't fight the dragon alone http://digitalfire.com
Calculation/Database Software for Ceramic Industry
--
Martin Howard on sun 7 nov 99
There is probably no simple answer and easy answer, other than plotting all
your glazes on triaxial paper, putting a line around those that are glossy,
those that are silk (lucky you if have them) and those that are matte.
Then the triaxial graph will show what of the great three groupings are our
of balance for your needs.
However, how to get hold of triaxial graph paper? It was available from
Chartwell in England. But they do not do it now. Has anyone got some? Could
you put a copy of it on line for us to take down and use?
I am just about to plot all my glazes and experiments in this way.
Martin Howard
Webbs Cottage Pottery
Woolpits Road
Great Saling
BRAINTREE
Essex CM7 5DZ
martin@webbscottage.co.uk
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