Ceramics group?

On Fri, 30 Jan 2004 13:29:32 GMT, "Noname" wrote:


"Bob Masta" wrote :

It should release
fairly easily, since the plaster will suck moisture away
from the contact surface and cause the clay to shrink
slightly.

Just a side question, can I depend on the amount of shrinkage? I want my
peices to be exactly 6 inches across so I need to know the shrinkage when I
(re) make my mold.


I'd like to elaborate on the good advice others have given.
There are different types and causes of shrinkage. The
first is going from slip to bone-dry, and the second is
going from bone-dry to fully-fired. As noted, the amounts
depend a lot on your clay. I haven't gotten into slip casting,
but I suspect the initial drying shrinkage may also depend
on how heavily deflocculated the slip is. (A deflocculant
is an additive like sodium silicate that makes the slip more
fluid with less water.)

It's been my experience that many clays don't shrink at
all in going from bone-dry to bisque. The shrinkage only
comes when they start to vitrify. I've used this to advantage
on pieces that needed to be a certain dimension after
firing, since you can sand, file, or grind the greenware
before firing. (Possible after bisque, but *much* harder.)
Then glaze at low-fire temperatures to keep the same
size. Note that this is not a good method for dinnerware
or vases, since the unvitrified clay will never really be
waterproof, your best glazing efforts not withstanding.
And you will need a really low-expansion glaze to keep
it from crazing.

Hope this helps!




Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com

Just a side question, can I depend on the amount of shrinkage? I
want
my
peices to be exactly 6 inches across so I need to know the shrinkage
when
I
(re) make my mold.

Grandpa always said, "...give the hardest job to the laziest man...he'll
find the
easiest way to do it..." and Grandpa was right, gods rest his soul :)

Take a kid's plastic ruler, one with raised numbers and lines on it.
Cut a slab of clay at least as long and as wide as the ruler,
then turn the ruler upside down and press to imprint the numbers into it.
Fire that piece as you normally would.
When it's fired and cool, lay the ruler next to it,
and with a pen or marker, mark the "real"
measurements next to the edge.

There's your shrinkage guide for YOUR clay.
Make one for each clay you use.

To find 6 inches, look until you see the "real" six inch mark,
and then read what the clay size has to be to shrink to 6"

Thanks to someone on Clayart for that suggestion, not me.
Best,
Wayne Seidl

Hello

There will be alot of trial and error in what you are attempting for a
first - timer.

May I suggest going to one of the "hobby" ceramics shops and asking them
how much they would charge to do the mold making for you? Many of them
have mold
making facilities to add fresh designs to their collection for their
surface decorating clientele. Having the molds made for you may speed-up
the results you want from this endeavor. Of course there is the process
which may be intriguing to you that's different than a results oriented
intent. At any rate those hobby serving mold-makers have alot of
knowledge and experience to tap into, maybe working for one part-time or
just inquiring will get you the knowledge and experience you need to go
on with your small house making project. Have fun and good luck.
Nancy Jane





v

i have a batch of cheap old wood rulers and i glue a fired clay ruler on the
back of the 'original" ruler to record shrinkage of all the clays i use. you
can readily see the start & finished size of the clay.

steve



Subject: Shrinkage
From: "wayneinkeywest"
Date: 1/31/2004 12:50 PM Pacific Standard Time
Message-id:


Just a side question, can I depend on the amount of shrinkage? I
want
my
peices to be exactly 6 inches across so I need to know the shrinkage
when
I
(re) make my mold.

Grandpa always said, "...give the hardest job to the laziest man...he'll
find the
easiest way to do it..." and Grandpa was right, gods rest his soul :)

Take a kid's plastic ruler, one with raised numbers and lines on it.
Cut a slab of clay at least as long and as wide as the ruler,
then turn the ruler upside down and press to imprint the numbers into it.
Fire that piece as you normally would.
When it's fired and cool, lay the ruler next to it,
and with a pen or marker, mark the "real"
measurements next to the edge.

There's your shrinkage guide for YOUR clay.
Make one for each clay you use.

To find 6 inches, look until you see the "real" six inch mark,
and then read what the clay size has to be to shrink to 6"

Thanks to someone on Clayart for that suggestion, not me.
Best,
Wayne Seidl










steve graber

If shrinkage were only that easy. The shrinkage your measuring is only
linear. Have you considered the shrinkage across the width of say a
bowl?

When a bowl is thrown on the wheel you create compression in the clay at
the base and you stretch the clay at the rim. So when the bowl is
drying it contracts in different ways.

The easiest way I can explain this is if you think of a bag with a
drawstring neck. As you tighten the drawstring the bag closes in
towards the middle.

This is the way the clay behaves in a thrown bowl. If you want a
specific diameter and height you have to make allowances for the rim to
contract making it smaller in diameter and it rises up as it draws in,
therefore making it higher.

Tricky old business if you need to make a specific finished size.

Practice practice is the only way.

Good luck


i have a batch of cheap old wood rulers and i glue a fired clay ruler on the
back of the 'original" ruler to record shrinkage of all the clays i use. you
can readily see the start & finished size of the clay.

steve



Subject: Shrinkage
From: "wayneinkeywest"
Date: 1/31/2004 12:50 PM Pacific Standard Time
Message-id:


Just a side question, can I depend on the amount of shrinkage? I
want
my
peices to be exactly 6 inches across so I need to know the shrinkage
when
I
(re) make my mold.

Grandpa always said, "...give the hardest job to the laziest man...he'll
find the
easiest way to do it..." and Grandpa was right, gods rest his soul :)

Take a kid's plastic ruler, one with raised numbers and lines on it.
Cut a slab of clay at least as long and as wide as the ruler,
then turn the ruler upside down and press to imprint the numbers into it.
Fire that piece as you normally would.
When it's fired and cool, lay the ruler next to it,
and with a pen or marker, mark the "real"
measurements next to the edge.

There's your shrinkage guide for YOUR clay.
Make one for each clay you use.

To find 6 inches, look until you see the "real" six inch mark,
and then read what the clay size has to be to shrink to 6"

Thanks to someone on Clayart for that suggestion, not me.
Best,
Wayne Seidl










steve graber

--
JohnB

"Nancy Albin" wrote :

There will be alot of trial and error in what you are attempting for a
first - timer.

...and error and error and error... apparently!

May I suggest going to one of the "hobby" ceramics shops and asking them
how much they would charge to do the mold making for you?

That's a great idea, and I will expand my search for such a place. So
far, the ceramic places I've visited simply purchase pre-cast peices for
"Paint your own" ceramics. One lady pours molds, but only premade molds.

I suspect I will have to go towards Orlando to find anyone who does
their own work.

"Nancy Albin" wrote ;

Of course there is the process
which may be intriguing to you that's different than a results oriented
intent.

Oh!... and, BTW, I poured slip into my first one-part mold yesterday and
it worked! Today I am making part two of a three-part mold.

Of course, there is still firing and ect to do, but at least now I have
something to fire besides funny looking clay scraps.

Trial and error indeed...

sounds like you are moving right along !
NJ





v

May I suggest you check your local library for a magazine called Popular
Ceramics. It bills itself as "the original ceramic hobby magazine". It
has some excellent information on slip casting, pouring, making molds,
decorating, etc. I make molds from my own original work and have found
this source most helpful. In the magazine, you will find many sources
for the type of ware you seek. You can buy bisqued ware for decorating,
molds to pour you own, or supplies and information on how to make your
own molds. They have also had excellent articles on firing, kiln
maintenance, and studio safety.

Good luck,

Jan C.

Have you tried www.aftosa.com ? They have some interesting links which may
take you to folks who will make the molds for you. Perhaps, they may even
have links to the exact product you are looking for. Steve in Tampa, FL.


"Jan Clauson" wrote in message
hlink.net...

May I suggest you check your local library for a magazine called Popular
Ceramics. It bills itself as "the original ceramic hobby magazine". It
has some excellent information on slip casting, pouring, making molds,
decorating, etc. I make molds from my own original work and have found
this source most helpful. In the magazine, you will find many sources
for the type of ware you seek. You can buy bisqued ware for decorating,
molds to pour you own, or supplies and information on how to make your
own molds. They have also had excellent articles on firing, kiln
maintenance, and studio safety.

Good luck,

Jan C.