Anna Woolf on mon 30 apr 07
Hi,
I have been using this 04 Majolica glaze for more than ten years, with
wonderful results. Over the last few firings, however, I have pieces
shivering!! The problem has gradually gotten worse, until this morning when
I unloaded a kiln with absolutely NO usable pieces! When I first noticed
the problem, I started making adjustments to try to correct the problem
(being obsessive about dust on the feet- the problem started on the feet of
some forms, adding a 1 hour soak to the glaze firing, adjusting the glaze
thickness, etc.) The problem is just getting worse. I know a shivering
glaze should be thrown out, but this glaze-clay combo worked for my mentor
and has since worked for me for more than ten years.
04 Majolica:
Frit 3124 - 840.3 g
EPK - 126.1 g
Bar. Carb. - 33.6 g
Zircopax - 126.1 g
Bentonite - 10. g
I use this (and always have) on EM 100 #10 White Earthenware Clay through
Laguna. I have thrown out several batches of this glaze and started over
fresh in case I made a mistake measuring. The glaze from this morning's
disaster was all new, except for a small portion of the Frit 3124 that I
needed to complete the recipe.
Some of my newest thoughts about this problem are:
? Did I switch from Superpax to Zircopax in the past and not notice - would
this make a difference?
? I used to fire my bisque pieces together with my glaze pieces at a slow
setting- both are 04 -, now, due to increased production, I have started
doing separate firings-bisque on slow and glaze on fast?
? Could my worn trimming tools be creating a burnished area that doesn't
accept the glaze? I have two favorite trimming tools that I haven't found
replacements for and they are just about worn down to the nub. They do
create a burnish, but I give that part a rub with a damp sponge at the end.
Is that rub not enough?
? Has there been a change in the manufacture or origin of one of my glaze
chems that I am unaware of?
Thanks for any suggestions,
Anna
Snail Scott on mon 30 apr 07
>Date: Mon, 30 Apr 2007 11:20:50 -0500
>From: Anna Woolf
>Subject: old tried & true glaze begins shivering
>
>I have been using this 04 Majolica glaze for more than ten years, with
>wonderful results. Over the last few firings, however, I have pieces
>shivering!!
Most of your theories - dust, burnished surfaces,
etc, will not account for shivering. They would
account for crawling, possibly even to the point of
glaze falling off the clay during firing and leaving
a bald spot. Shivering, however, is caused by an
incompatible coefficient of explansion, regardless
of the glaze's adhesion to the clay. The visible
difference between crawling and shivering is that
crawling occurs during the firing, and the bare
patches will have smooth melted edges. Shivering
occurs during cooling, after the glaze has hardened,
so the edges of the bare patches are sharp and rough.
Since this is an old recipe, your idea about a change
in materials is very likely the case - either for the
clay body or the glaze or even both. Shivering is the
result of the failure of the hardened glaze to shrink
at the same rate as the cooling clay, forcing little
shards of glaze to pop off, especially at sharp edges.
The classic solution, regardless of which material is
at fault, is to increase the silica in either the clay
OR in the glaze. This sounds counterintuitive, but
silica behaves very differently in the glaze melt than
in does in the less-melted clay, so it's really two
different solutions to fixing the CoE, which just
happen to use the same material.
-Snail
Dinah Steveni on mon 30 apr 07
Try sintering or firing the glaze onto the bisque ware at a lower temp than
the final melt; then apply your colors on the sintered body. Test this
effect first. Daphne Carnegie's Tin-Glazed Earthenware cites proper formula
for sintering. Good results I found.
Rub burnished areas with some sandpaper, then sponge off the dust. You need
proper take-up of the glaze. Sponging areas won't really be the answer will
it?
Dinah Steveni
----- Original Message -----
From: "Anna Woolf"
To:
Sent: Monday, April 30, 2007 9:20 AM
Subject: old tried & true glaze begins shivering
> Hi,
> I have been using this 04 Majolica glaze for more than ten years, with
> wonderful results. Over the last few firings, however, I have pieces
> shivering!! The problem has gradually gotten worse, until this morning
when
> I unloaded a kiln with absolutely NO usable pieces! When I first noticed
> the problem, I started making adjustments to try to correct the problem
> (being obsessive about dust on the feet- the problem started on the feet
of
> some forms, adding a 1 hour soak to the glaze firing, adjusting the glaze
> thickness, etc.) The problem is just getting worse. I know a shivering
> glaze should be thrown out, but this glaze-clay combo worked for my mentor
> and has since worked for me for more than ten years.
>
> 04 Majolica:
> Frit 3124 - 840.3 g
> EPK - 126.1 g
> Bar. Carb. - 33.6 g
> Zircopax - 126.1 g
> Bentonite - 10. g
>
> I use this (and always have) on EM 100 #10 White Earthenware Clay through
> Laguna. I have thrown out several batches of this glaze and started over
> fresh in case I made a mistake measuring. The glaze from this morning's
> disaster was all new, except for a small portion of the Frit 3124 that I
> needed to complete the recipe.
>
> Some of my newest thoughts about this problem are:
>
> ? Did I switch from Superpax to Zircopax in the past and not notice -
would
> this make a difference?
>
> ? I used to fire my bisque pieces together with my glaze pieces at a slow
> setting- both are 04 -, now, due to increased production, I have started
> doing separate firings-bisque on slow and glaze on fast?
>
> ? Could my worn trimming tools be creating a burnished area that doesn't
> accept the glaze? I have two favorite trimming tools that I haven't found
> replacements for and they are just about worn down to the nub. They do
> create a burnish, but I give that part a rub with a damp sponge at the
end.
> Is that rub not enough?
>
> ? Has there been a change in the manufacture or origin of one of my glaze
> chems that I am unaware of?
>
> Thanks for any suggestions,
> Anna
>
>
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Ron Roy on tue 1 may 07
Hi Anna,
It's not the glaze - unless some materials are not what you think they are.
If a mixture with new materials does the same thing it must be the clay.
Perhaps you could ask you clay supplier to give you the names of other
people who are using that same clay - or ask here on ClayArt
Some clay companies provide expansion data on their bodies - if you can get
that you may be able to find another clay that will fit that glaze.
Why you would use a toxic expensive material like barium carbonate when
plain old whiting would do the exact some thing in this glaze is beyound
me.
RR
>Hi,
>I have been using this 04 Majolica glaze for more than ten years, with
>wonderful results. Over the last few firings, however, I have pieces
>shivering!! The problem has gradually gotten worse, until this morning when
>I unloaded a kiln with absolutely NO usable pieces! When I first noticed
>the problem, I started making adjustments to try to correct the problem
>(being obsessive about dust on the feet- the problem started on the feet of
>some forms, adding a 1 hour soak to the glaze firing, adjusting the glaze
>thickness, etc.) The problem is just getting worse. I know a shivering
>glaze should be thrown out, but this glaze-clay combo worked for my mentor
>and has since worked for me for more than ten years.
>
>04 Majolica:
>Frit 3124 - 840.3 g
>EPK - 126.1 g
>Bar. Carb. - 33.6 g
>Zircopax - 126.1 g
>Bentonite - 10. g
>
>I use this (and always have) on EM 100 #10 White Earthenware Clay through
>Laguna. I have thrown out several batches of this glaze and started over
>fresh in case I made a mistake measuring. The glaze from this morning's
>disaster was all new, except for a small portion of the Frit 3124 that I
>needed to complete the recipe.
>
>Some of my newest thoughts about this problem are:
>
>? Did I switch from Superpax to Zircopax in the past and not notice - would
>this make a difference?
>
>? I used to fire my bisque pieces together with my glaze pieces at a slow
>setting- both are 04 -, now, due to increased production, I have started
>doing separate firings-bisque on slow and glaze on fast?
>
>? Could my worn trimming tools be creating a burnished area that doesn't
>accept the glaze? I have two favorite trimming tools that I haven't found
>replacements for and they are just about worn down to the nub. They do
>create a burnish, but I give that part a rub with a damp sponge at the end.
> Is that rub not enough?
>
>? Has there been a change in the manufacture or origin of one of my glaze
>chems that I am unaware of?
>
>Thanks for any suggestions,
>Anna
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Anna Woolf on thu 3 may 07
Thanks for all of your responses. I have been concerned with my use of
barium for quite a while now. Have really only been holding on to this
glaze because of it's great performance (up 'til now)! I had an "if it
ain't broke..." attitude about the glaze, and was very mindful of proper
safety practices with the barium. But, it feels like the universe is
telling me that it's time to throw out the old recipe and begin
experiments with some new, less toxic materials. Not trying to me all
mystical with the "universe" stuff, but what a coincidence that this glaze
begins to act-up just at the time I am expecting my first child. Seems like
it is time for me to take the Barium out of my (and her) work space!
So, it's back to small batches and test tiles for me! I'm open to any
non-toxic recipes you all may have!
Thanks,
Anna
Dan Semler on thu 3 may 07
Hi Anna,
I've been monkeying with barium carb subs a bit of late. If you
want to send me the recipe I'll take a look and see if I can make some
suggestions. Offlist or onlist - up to you. I haven't really been
followibng this thread in detail, so if you do want me to take a look,
let me know the firing temp and what colourants you are using with it,
if any.
thanx
D
Anna Woolf on fri 4 may 07
Hi Daniel,
Here is a portion of my original post:
"I have been using this 04 Majolica glaze for more than ten years, with
wonderful results. Over the last few firings, however, I have pieces
shivering!! The problem has gradually gotten worse, until this morning when
I unloaded a kiln with absolutely NO usable pieces! When I first noticed the
problem, I started making adjustments to try to correct the problem (being
obsessive about dust on the feet- the problem started on the feet of some
forms, adding a 1 hour soak to the glaze firing, adjusting the glaze
thickness, etc.) The problem is just getting worse. I know a shivering glaze
should be thrown out, but this glaze-clay combo worked for my mentor and has
since worked for me for more than ten years.
04 Majolica:
Frit 3124 - 840.3 g
EPK - 126.1 g
Bar. Carb. - 33.6 g
Zircopax - 126.1 g
Bentonite - 10. g
I use this (and always have) on Miller Clay EM 100 #10 White Earthenware
Clay through Laguna. I have thrown out several batches of this glaze and
started over fresh in case I made a mistake measuring. The glaze from this
morning's disaster was all new, except for a small portion of the Frit 3124
that I needed to complete the recipe." - I use mason stains mixed with Frit
3124 (1:2-3) for colorants.
I have made the decision to focus all of my studio efforts on testing new
clay/glaze combos. Any help in removing the Barium from this glaze will be
very appreciated. I took the "Kitchen Recipe" route of Glazing in college,
while my husband actually learned the chemistry of it. But after years of
dis-use, his glaze chem skills have just about rusted away!! My lack of
confidence in being able to "do the math" has kept me using the Barium when
I really would rather banish it from my studio. With our first child on the
way, I find it really is time to move on.
Thanks in advance for any suggestions you might have,
Anna
Anna Woolf on sun 6 may 07
Hi Ron,
Yes, I think so, - the clay has changed?
With this clay glaze combo acting -up so bad, I have decided to take this as
an opportunity to rid my studio of the Barium Carb and to experiment with
getting majolica to go ^6. I have just gotten a mess of new glaze chems and
will start testing new recipes and new clays this week. I must say that I
allowed my "math phobia" (or call it laziness) to prevent me from ever
learning the chemistry of glaze formulation. So I am stuck with the old
kitchen recipe - trial and error method of glazing. I have downloaded a
free trial of GlazeMaster 2.3 and will give it a try, but I know myself and
know that I will be itching to "do something" about the problem long before
I really learn the chemistry behind it. Foolish, I know but my "Don't just
stand there, DO SOMETHING" instinct is quite strong!
Thanks your help,
Anna
Dan Semler on sun 6 may 07
Hi Anna,
First, apologies for the slow turnaround on this.
Ok, so it seems that this glaze is basically frit and EPK, there =20
being only about 3% barium carbonate in it. Removing it can be done =20
simply by subbing in 17 grams or whiting or 25 grams of strontium =20
carbonate. I suspect the whiting may be the better choice - should be =20
cheaper anyway. But you are already on the high side for calcia in a =20
cone 04 glaze, at least according to one set of limits. The advantage =20
though of using whiting is that it will be less likely to perturb =20
colours you have gotten used to, as the glaze is already full of it. =20
BTW, you'll need to retotal it all back to 1000gram batch as these =20
will now be off a little for your bentonite/zircopax percentages. But =20
then again for a quick test I wouldn't worry, its only 16 or so in a =20
1000.
But to the other problem. You have a shivering problem, which it =20
sounds like the claybody may be causing. So we ideally want to push =20
the expansion of this glaze up a bit. Both strontium and calcium carb. =20
on paper reduce the expansion a bit. That said, I'm not expert at =20
earthenware - well in fact nowhere near. So I tried substituting a =20
higher expansion frit (3134) but then we end up adding a bunch of =20
stuff and get ourselves back close to where we started, plus you'd =20
have to melt real silica. Ideally I'd like more potash or soda in =20
there to push the expansion up. OK, so what to do ?
Try the subs above and check them closely for shivering problems.
Let me know what other frits you have, or have ready access to and =20
I'll see what might be concocted. There are some less commonly used =20
frits that have higher soda contents that might help here, but its not =20
much good if you can't get them.
Thanx
D
Anna Woolf on mon 7 may 07
Hi Dan,
I tried to e-mail this directly to you this morning but it was returned as
undeliverable-
Thanks Dan!
I'll be in the studio today working on tests of different majolica glazes.
I found 3 low fire and 2 ^6's that I will try this week and I will also make
a test batch with your subs and let you know. I am most hoping to find a ^6
because of the durability and plus I really fell in love with a couple of
the stonewares I used to make test pieces for this!
I'm pretty sure that I only have frit 3124 and 3134 at hand. My ceramic
supply place is over 3 hours away! And I just made the trip Friday to get
what I need for these tests. I might be able to talk them into shipping
some sample size packages of other frits, otherwise, it will be a few weeks
before I can get back down to Portland.
Again - Thanks so much! Your suggestions have been very helpful!
Now I'm off to the studio,
Anna
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