Stephani Stephenson on wed 2 apr 03
Becky Schroeder asked about how to release a clay relief tile from a
mold before the tile becomes too dry:
When you press or pour clay into a SHALLOW relief mold
it will usually start to pull away, on it's own, from the plaster in 15
minutes to a couple of hours, depending on
the the temperature, the dryness of plaster, the relative humidity,
wetness of clay, etc.
When you see it separate from the plaster, along the borders, you can
usually just turn the mold over and plop the piece out
With very shallow pieces all you have to do is stand the mold up on
end, gently angle it over and catch pieces with board or hand
(so they don't leap from the mold and plummet to the nearest hard
surface, thereby denting themselves!)
Some books show a way to remove pieces by placing mold upside down on
spacer boards, then tapping the backside of the mold with a mallet
(rubber mallet , or gently but firmly tap with wooden mallet but place
something over top of mold to prevent breaking the mold)
I don't use this method as I don't like hitting plaster molds, and
usually a mere 'light' thump will not do the job.
Either the tile will self release, as already mentioned, without the
thump, or it simply will NOT release, and the thump won't help very
much!
MEDIUM to DEEP relief pieces can be difficult to release, especially if
the relief areas in the piece are are somewhat vertical rather then
gradual , or if you start with wet clay: because as the clay releases
it shrinks, and the relief areas can get hung up in the process.
Then you are faced with having to dig the piece out, which mars it, or
hoping it will shrink enough to release when dry, which often is
unsuccessful
You can make an air purge mold, but that is too long a topic for now
However there is a simple way to use compressed air to release the
clay .
It is the best way I have found to release medium to deep relief
pieces from plaster molds , as follows :
Stand the mold on end, so the mold and still moist clay piece are
basically vertical.
Place a catch board, somewhat larger than the clay piece, horizontally
in front of the vertical mold
If you are really fancy, place the catch board on an angled surface,
maybe 30 degrees from horizontal, but that isn't crucial....
PUT ON SAFETY GLASSES OR GOGGLES!
shoot a little compressed air into the edge of the piece
by this I mean snuggle that air nozzle right up next to a place where
the clay meets the plaster,
usually near , but not on, a top corner
what you are going to do is force air down between the plaster wall
and the side/face of the clay piece.
experiment with this
sometimes if the air pressure is too high
and the clay is too wet, the air will dig a little air trench into
the clay.
if the relief is shallow and the piece is small, the clay may jetison
out of the mold and fly completely off the table
So, monkey with the air pressure and the technique.....
Sometimes you can go around the perimeter of the tile with the
compressed air , first separating it on all sides.
usually what happens, when you get good at it
is that one or two well placed 'poofs' release the tile, or one major
section of the tile
At this point I usually do sort of an all in one move
usually when I shoot the air with one hand
the other hand is cradling and tilting the mold so it is
a bit like the leaning tower of Pisa, maybe not even leaning quite that
much
clay side leaning down
for shallow or medium relief pieces, as the clay 'emerges' from the
mold in one area, I put down the air hose
(you can sling the hose over your shoulder so it doesn't drop to the
ground)
and with the free hand, guide the tile down to the board, especially if
it is large tile or clay piece
or , if deep relief, I actually pull/coax it out with the free hand,
tilting the mold more as it comes out
sometimes still introducing air as I go
(where did I get that third hand???? who knows? I always wonder about
that))
needless to say, if the mold is h-u-u-u-g-e and the relief is d-e-e-e-p,
get a helper to tilt and anchor the mold while you do the air and clay
dance!
Or they tilt the mold and shoot the air while you manage the clay and
catch board.
because the clay is still moist
it is pliable,
Naturally you try to not distort it
But if it gets out of square, or the last edge to release gets hung up
a bit
You can true up the piece with lengths of 2 X2 afterwards
place 2X2 on opposing sides of tile and press, to square up and
compress the piece slightly
if a piece is very deep relief, just ease it out gradually , with
pulling , not digging motions,
you can get the air hose further down into the mold and release little
by little
usually there is a point where it comes out quite nicely
with slurry or slip molds
if they don't release on their own
wait till the
slurry firms up to the point where it is like
regular moist clay.
I have added grog and/or paper pulp to deflocculated
clay casting slip to
make it more useful for tile pieces
and to reduce shrinkage
I also age the casting slip .
Note: if you are really doing slipcasting and want typical thin walls
+/- 1/4" and having problems with release
i would suggest that you redo the model and the mold to address
problems of undercuts
most molds I use for hand pressing allow for clay thickness of 1/2" or
5/8 to 3/4"
Stephani Stephenson
steph@alchemiestudio.com
http://www.alchemiestudio.com
Russel Fouts on thu 3 apr 03
Stephani,
>> Some books show a way to remove pieces by placing mold upside down on spacer boards, then tapping the backside of the mold with a mallet (rubber mallet , or gently but firmly tap with wooden mallet but place something over top of mold to prevent breaking the mold) I don't use this method as I don't like hitting plaster molds, and usually a mere 'light' thump will not do the job. Either the tile will self release, as already mentioned, without the thump, or it simply will NOT release, and the thump won't help very much! <<
I would think that if you left the mold upside down on spacers (1/2")
and left it to dry on it's own, there might be a pretty good chance that
the tile would drop out before it could get hung up.
I'm saving a lot of the stuff you're writing about tiles for later. I
love tiles but have never made many.
Russel
--
Russel Fouts
Mes Potes & Mes Pots
Brussels, Belgium
Tel: +32 2 223 02 75
Mobile: +32 476 55 38 75
Http://www.mypots.com
Home of "The Potters Portal"
Over 1800 Pottery Links!
Updated frequently
"Is the Hokey Pokey really what it's all about?"
Stephani Stephenson on thu 3 apr 03
hi Russel
that is true, for a flat tile or a tile with shallow relief, or a deeper
piece in a very well designed mold..
where the draft , or angling of the walls and projections, is
generous, i.e sloping , not 90 degrees..
(am groping for a better way to say that.....)
When pieces have unusually intricate , deep or radical relief
then they don't always drop out
they just shrink themselves around the mold relief projections
amazing how they can hang like that!
PS today I finally unpacked soome of the slide carousels, etc, from
NCECA
and to my delight I found
in the box
a CLAYART tee shirt!!!!!
what a pleasant surprise!
I love the fact that it sat there a couple of weeks, in the box,
keeping it's secret, without a peep!
whoever did this
thank you
Stephani
Russel Fouts wrote:
> Stephani,
>
> >> Some books show a way to remove pieces by placing mold upside down
on spacer boards, then tapping the backside of the mold with a mallet
(rubber mallet , or gently but firmly tap with wooden mallet but place
something over top of mold to prevent breaking the mold) I don't use
this method as I don't like hitting plaster molds, and usually a mere
'light' thump will not do the job. Either the tile will self release, as
already mentioned, without the thump, or it simply will NOT release,
and the thump won't help very much! <<
>
> I would think that if you left the mold upside down on spacers (1/2")
> and left it to dry on it's own, there might be a pretty good chance
that
> the tile would drop out before it could get hung up.
>
> I'm saving a lot of the stuff you're writing about tiles for later. I
> love tiles but have never made many.
>
> Russel
>
> --
>
> Russel Fouts
> Mes Potes & Mes Pots
> Brussels, Belgium
> Tel: +32 2 223 02 75
> Mobile: +32 476 55 38 75
>
> Http://www.mypots.com
> Home of "The Potters Portal"
> Over 1800 Pottery Links!
> Updated frequently
>
> "Is the Hokey Pokey really what it's all about?"
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