Tom Buck on mon 10 aug 98
Ms Busch:
Let me add my thoughts on this. Tony Hansen has advocated many
times that a glaze should always be in compression on the pot, ie, the
body should shrink a tiny bit more than the glaze, much, much less than a
millimetre difference but this amount is important. He has reported on his
tests that show a body's physical strength on firing more than doubles
when the glaze compresses the body ever so little, compared to a glaze
that shrinks a bit more than the body (and the glaze thereby goes into
tension and cracks).
Some of your problems surely stem from an unsatisfactory claybody
for your working methods. But if you prefer not the find a new body then
you'll will have to change your methods.
Firstly, avoid your Floating Blue recipe as is. Its expansion at
8x10-6 is way above the likely expansion level of the body (probably
around/below 7x10-6). This recipe analyzes as being oustide usual Limits
(best Seger unity formula), and it has "awkwardnesses" built-in.
I suggest you adopt Hansen's 5x20 glaze as your base glaze for C5.
It contains 20 weight per cent of Wollastonite, Ferro Frit 3134, Custer
(or G200 feldspar), EPK (or equal), and Flint. This mix has been
thoroughly tested by Tony and others and has a lot in its favor, espy its
7x10-6 expansion level.
Now, to get the float-blue effect, you will have to run some tests
with this new base. Do a five-part line blend and see if you get what you
like. The rutile will likely be between 2 & 3 wt%, the iron oxide red 1
wt%, and the Cobalt carb, 1-2%. Run these tests without the overglaze
first, and if one mix is suitable, then try it with the overglaze.
And as it was already noted, please in plates, etc., use a good
foot and glaze inside the foot (so foot has to be high enough to allow for
this). By having glaze on both sides of a pot one tends to have the forces
equalized.
Good tests. Til later. Peace.
Tom Buck ) tel: 905-389-2339
& snailmail: 373 East 43rd St. Hamilton ON L8T 3E1 Canada
(westend Lake Ontario, province of Ontario, Canada).
Olivia T Cavy on wed 12 aug 98
Tom,
FYI when I first tried Tony's 5 part glaze, the first colorants I tried
were the floating blue colorants. (I label his Floating Magic on my glaze
bucket.) I did not experiment with the quantity of rutile, but it looked
like the 2 glazes were vastly different in appearance. I discussed this
briefly with Tony, and (if I remember correctly) he pointed out that the
original floating blue glaze was runnier than his glaze base. Actually in
my experience, his glaze base pretty much stays where you put it, but not
as much as a matt glaze.
I've continued to use both glazes now for a few years, but I don't think
there is any way that Tony's glaze will ever look remotely similar to
Floating Blue. I like both glazes, and use them both in combination. I
also find that many times if I fire a previously bisqued pot with Tony's
glaze (Floating Magic) in a second bisque firing to ^06, I get
interesting crackling patterns. I then re-dip the pot in a contrasting
color glaze like white, and fire up to temperature, to end up with a
marble-like appearance. BTW I use ^6 porcelain (mostly grolleg) and
Standard Ceramics ^6 white stoneware clay #181.
Tony's glaze is wonderful (thanks Tony) but floating blue, it ain't.
BTW when I first used floating blue I had crawling problems. I had many
suggestions from Clayarters about possible causes, but finally figured
out that on my clays it crawls if applied too thickly and unevenly.
Bonnie
Bonnie D. Hellman
Pittsburgh, PA
work email: bdh@firstcaptl.com or oliviatcavy@juno.com
home email: mou10man@sgi.net
On Mon, 10 Aug 1998 09:49:57 EDT Tom Buck writes:
>----------------------------Original
>message----------------------------
>Ms Busch:
> Let me add my thoughts on this. Tony Hansen has advocated many
>times that a glaze should always be in compression on the pot, ie, the
>body should shrink a tiny bit more than the glaze, much, much less
>than a
>millimetre difference but this amount is important. He has reported on
>his
>tests that show a body's physical strength on firing more than doubles
>when the glaze compresses the body ever so little, compared to a glaze
>that shrinks a bit more than the body (and the glaze thereby goes into
>tension and cracks).
> Some of your problems surely stem from an unsatisfactory
>claybody
>for your working methods. But if you prefer not the find a new body
>then
>you'll will have to change your methods.
> Firstly, avoid your Floating Blue recipe as is. Its expansion
>at
>8x10-6 is way above the likely expansion level of the body (probably
>around/below 7x10-6). This recipe analyzes as being oustide usual
>Limits
>(best Seger unity formula), and it has "awkwardnesses" built-in.
> I suggest you adopt Hansen's 5x20 glaze as your base glaze for
>C5.
>It contains 20 weight per cent of Wollastonite, Ferro Frit 3134,
>Custer
>(or G200 feldspar), EPK (or equal), and Flint. This mix has been
>thoroughly tested by Tony and others and has a lot in its favor, espy
>its
>7x10-6 expansion level.
> Now, to get the float-blue effect, you will have to run some
>tests
>with this new base. Do a five-part line blend and see if you get what
>you
>like. The rutile will likely be between 2 & 3 wt%, the iron oxide red
>1
>wt%, and the Cobalt carb, 1-2%. Run these tests without the overglaze
>first, and if one mix is suitable, then try it with the overglaze.
> And as it was already noted, please in plates, etc., use a
>good
>foot and glaze inside the foot (so foot has to be high enough to allow
>for
>this). By having glaze on both sides of a pot one tends to have the
>forces
>equalized.
> Good tests. Til later. Peace.
>
>Tom Buck ) tel: 905-389-2339
>& snailmail: 373 East 43rd St. Hamilton ON L8T 3E1 Canada
>(westend Lake Ontario, province of Ontario, Canada).
>
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