Slumping and firing

Hi folks :-)

Okay - I have been wondering how to fire a couple of pieces. When they are
all put together, they will have surfaces that won't be touching the oven
shelf, and I worry about slumping occurring. Especially one of the pieces
just can not do that (a clock face).

So, I was thinking - should I maybe bisque fire, glaze fire at eg. 1270,
mount the pieces and finish glazing and refire at eg. 1250? Would
re-glaze-firing at a lower temperature than original glaze firing help
ensure that the pieces don't slump? Or do they get just as soft on the
second firing?

Marianne

Make some support pieces out of the same clay, and make them cone shaped
so that they are stable but the area in contact with the piece itself
are minimal, so that if they stick to the piece, the damage is minimal.
These are called sacrificial supports; the Tang Potters used them to
support those wonderful horses and camels they made during the glaze
firing.

Steve
Bath
UK


In article , Bubbles_
writes
Hi folks :-)

Okay - I have been wondering how to fire a couple of pieces. When they are
all put together, they will have surfaces that won't be touching the oven
shelf, and I worry about slumping occurring. Especially one of the pieces
just can not do that (a clock face).

So, I was thinking - should I maybe bisque fire, glaze fire at eg. 1270,
mount the pieces and finish glazing and refire at eg. 1250? Would
re-glaze-firing at a lower temperature than original glaze firing help
ensure that the pieces don't slump? Or do they get just as soft on the
second firing?

Marianne



--
Steve Mills
Bath
UK

"Steve Mills" wrote in message
...
Make some support pieces out of the same clay, and make them cone shaped
so that they are stable but the area in contact with the piece itself
are minimal, so that if they stick to the piece, the damage is minimal.
These are called sacrificial supports; the Tang Potters used them to
support those wonderful horses and camels they made during the glaze
firing.

Hi Steve!

I know what you mean, but if you imagine a clock-face disk, for example,
with roman numerals around it - might not the whole face slump around the
numerals? Or, if I turn it the other way, even if I do support it with
"sacrificials", might it not slump anyway?

I haven't tried my theories out, as this clock is for my teacher's workshop,
as her plastic clock died on her and I just don't approve of anything
plastic in a potter's workshop, as long as the same thing can be made out of
clay! :-D

I go on holiday in July, so I hope to have the clock all ready for her the
last Friday lesson before I leave.

Marianne

So are you intending to fire it face down?

Is not the back of the Clock flat? or have you built it up.

The Clocks I have made have all been flat backed because the hanging
provision is part of the case containing the movement

The current Kitchen clock at home is a fairly freeform flat shape,
mounted on a black stained wooden panel with the movement held onto the
panel by the shaft with the hands on it, surrounded by a wooden box with
the hanging hook on that. Saves trying to build all that onto the
ceramic.

Steve
Bath
UK


In article , Bubbles_
writes
Hi Steve!

I know what you mean, but if you imagine a clock-face disk, for example,
with roman numerals around it - might not the whole face slump around the
numerals? Or, if I turn it the other way, even if I do support it with
"sacrificials", might it not slump anyway?

I haven't tried my theories out, as this clock is for my teacher's workshop,
as her plastic clock died on her and I just don't approve of anything
plastic in a potter's workshop, as long as the same thing can be made out of
clay! :-D

I go on holiday in July, so I hope to have the clock all ready for her the
last Friday lesson before I leave.

Marianne



--
Steve Mills
Bath
UK

"Steve Mills" wrote in message
...
So are you intending to fire it face down?

I cheated this time and dug the pattern in, instead of adding it to. So,
yes, intending to bisque fire face down. Will be worse with the glaze
firing, though, as that has to be face up. I have made a collar around the
whole face, for better dust-protection and deep enough to contain the
clockwork.

Is not the back of the Clock flat? or have you built it up.

see above

The Clocks I have made have all been flat backed because the hanging
provision is part of the case containing the movement

My clockworks have no hanging provision attached, so I figured on making
that in the collar of the clock sides.

The current Kitchen clock at home is a fairly freeform flat shape,
mounted on a black stained wooden panel with the movement held onto the
panel by the shaft with the hands on it, surrounded by a wooden box with
the hanging hook on that. Saves trying to build all that onto the
ceramic.

I have a cylinder with a face - and then I have a smaller box inside which
will be closed to facilitate reopening to change batteries. The trouble is
that this clock is going in a ceramics workshop, so it needsto be - shall I
say - dust efficientl

When I do fire it "on its back" for the glaze firing, that will probably be
my greatest slumping risk. I do make some supports now and then and can only
hope I have onesto fit under the clock face so it stays flat.

Marianne

In message , Bubbles_
writes

"Steve Mills" wrote in message
...
So are you intending to fire it face down?

I cheated this time and dug the pattern in, instead of adding it to. So,
yes, intending to bisque fire face down. Will be worse with the glaze
firing, though, as that has to be face up. I have made a collar around the
whole face, for better dust-protection and deep enough to contain the
clockwork.

Is not the back of the Clock flat? or have you built it up.

see above

The Clocks I have made have all been flat backed because the hanging
provision is part of the case containing the movement

My clockworks have no hanging provision attached, so I figured on making
that in the collar of the clock sides.

The current Kitchen clock at home is a fairly freeform flat shape,
mounted on a black stained wooden panel with the movement held onto the
panel by the shaft with the hands on it, surrounded by a wooden box with
the hanging hook on that. Saves trying to build all that onto the
ceramic.

I have a cylinder with a face - and then I have a smaller box inside which
will be closed to facilitate reopening to change batteries. The trouble is
that this clock is going in a ceramics workshop, so it needsto be - shall I
say - dust efficientl

When I do fire it "on its back" for the glaze firing, that will probably be
my greatest slumping risk. I do make some supports now and then and can only
hope I have onesto fit under the clock face so it stays flat.

Marianne


Hi Marianne

I work in porcelain and fire to around 1250, mostly leaving work bisque.
I really don't glaze much at all, and then only to use a good white tin
glaze as a base for lustres and onglaze colours. Glazes really aren't
my thing at all!

I often make pieces that really do risk slumping at high temperature.
Years ago someone suggested using high temperature ceramic fibre as a
support. I had to use this technique a couple of weeks back and it does
work for me. I wondered if it might help you? Any way of packing the
back of your clock with the fibre? It doesn't stick to bisque porcelain
but I'm sure you'd need to keep it away from glaze. I wonder if Steve
can add anything to this?

Regards
Susie
--
Susie Thompson, Isle of Arran
SPAM BLOCK IN OPERATION! Replace "deadspam.com" with "arrandragons.co.uk" to
reply by e-mail.

"SusieThompson" wrote in message
...

I often make pieces that really do risk slumping at high temperature.
Years ago someone suggested using high temperature ceramic fibre as a
support. I had to use this technique a couple of weeks back and it does
work for me. I wondered if it might help you? Any way of packing the
back of your clock with the fibre? It doesn't stick to bisque porcelain
but I'm sure you'd need to keep it away from glaze. I wonder if Steve can
add anything to this?

That sounds like a great idea, Susie, but I have never seen that here in
Switzerland. That might just be because I don't know what it is, though! Now
I know, I will ask my teacher and mmy dealer about it. Thanks!

Marianne

In article , SusieThompson
writes

Hi Marianne

I work in porcelain and fire to around 1250, mostly leaving work bisque.
I really don't glaze much at all, and then only to use a good white tin
glaze as a base for lustres and onglaze colours. Glazes really aren't
my thing at all!

I often make pieces that really do risk slumping at high temperature.
Years ago someone suggested using high temperature ceramic fibre as a
support. I had to use this technique a couple of weeks back and it does
work for me. I wondered if it might help you? Any way of packing the
back of your clock with the fibre? It doesn't stick to bisque porcelain
but I'm sure you'd need to keep it away from glaze. I wonder if Steve
can add anything to this?

Regards
Susie


That is a very reliable technique;
I use pieces of Ceramic Fibre in between pots in a biscuit firing, but
the one occasion I used it in a glaze, cleaning off the fibre remaining
on the piece after the firing needed care AND a good respirator (very
important that). I was using a fairly high iron clay, and firing to cone
9 right over in reduction, so that will have made it stick more than a
straight oxidising electric firing would.

--
Steve Mills
Bath
UK

In message , Steve Mills
writes
In article , SusieThompson
writes

Hi Marianne

I work in porcelain and fire to around 1250, mostly leaving work bisque.
I really don't glaze much at all, and then only to use a good white tin
glaze as a base for lustres and onglaze colours. Glazes really aren't
my thing at all!

I often make pieces that really do risk slumping at high temperature.
Years ago someone suggested using high temperature ceramic fibre as a
support. I had to use this technique a couple of weeks back and it does
work for me. I wondered if it might help you? Any way of packing the
back of your clock with the fibre? It doesn't stick to bisque porcelain
but I'm sure you'd need to keep it away from glaze. I wonder if Steve
can add anything to this?

Regards
Susie


That is a very reliable technique;
I use pieces of Ceramic Fibre in between pots in a biscuit firing, but
the one occasion I used it in a glaze, cleaning off the fibre remaining
on the piece after the firing needed care AND a good respirator (very
important that). I was using a fairly high iron clay, and firing to cone
9 right over in reduction, so that will have made it stick more than a
straight oxidising electric firing would.

Thanks Steve. I'd forgotten to warn Marianne that ceramic fibre is a
hazardous material. I always wash my hands carefully after using it.

I've been thinking through how I use the fibre, and I suspect that if I
packed/supported something too rigidly with it, there could be the
possibility that the clay might split if it was trapped in one position.
The things I make tend to flex and move around in firing. Any thoughts
Steve?
Susie
--
Susie Thompson, Isle of Arran
SPAM BLOCK IN OPERATION! Replace "deadspam.com" with "arrandragons.co.uk" to
reply by e-mail.

In article , SusieThompson
writes
Thanks Steve. I'd forgotten to warn Marianne that ceramic fibre is a
hazardous material. I always wash my hands carefully after using it.

I've been thinking through how I use the fibre, and I suspect that if I
packed/supported something too rigidly with it, there could be the
possibility that the clay might split if it was trapped in one position.
The things I make tend to flex and move around in firing. Any thoughts
Steve?
Susie

You'd have to pack it pretty tight to do that; most CF shrinks
noticeably during its first firing anyway (except 1400 grade), The
current *body soluble* stuff (Calcium-Magnesium-Silicate) does as well,
tho' it's not yet as good at high temperatures as the old stuff
(Alumina-Silica).

For bisc. firing stacks of bowls I have been using and re-using the same
box full of fibre squares for the last 10 years (true!). They stop them
pinning each other together and cracking, I use 3 to a layer.

I'm away for a week now, see you all later.

Steve
--
Steve Mills
Bath
UK