Randall Moody on mon 12 mar 12
If you have not tried this already, try scrubbing the mold out with some
water and a fine bristle scrub brush.
On Mon, Mar 12, 2012 at 6:41 PM, Roets Liselot wrote:
> Dear,
>
> first of all i would like to excuse myself, my active english isn't verr=
y
> good.
>
> now to my question:
>
> working with paper clay slip, made from pulp and a commercial molding
> clay.
>
> after experimenting for a few times in the same cast, the cast seems
> ruined,
> even with ordinary slip, the work sticks to the plaster and is verry/ if
> not
> impossible to remove.
>
> what could i have done wrong? Anyone any experience with slip casting
> paper
> clay in a plaster mold?
>
> thank you verry much,
> Liselot.
>
--
Randall in Atlanta
http://wrandallmoody.com
Roets Liselot on mon 12 mar 12
Dear,=3D20
first of all i would like to excuse myself, my active english isn't verr=
=3D
y good.
now to my question:
working with paper clay slip, made from pulp and a commercial molding cl=
=3D
ay.
after experimenting for a few times in the same cast, the cast seems rui=
=3D
ned,=3D20=3D20
even with ordinary slip, the work sticks to the plaster and is verry/ if=
=3D
not=3D20
impossible to remove.=3D20=3D20
what could i have done wrong? Anyone any experience with slip casting pa=
=3D
per=3D20
clay in a plaster mold?=3D20=3D20
thank you verry much,
Liselot.
Roets Liselot on tue 13 mar 12
Thank you for your quick response,
I did clean the mold with water and a toothbrush before using it a second=
=3D
time.
plasterjfl@AOL.COM on tue 13 mar 12
Liselot,
I've not used paperclay, as such, but I am a long time slip caster/mold
maker, so I'll share this.
Because I've farmed myself out as a mold maker I sometimes have artists,
or artists' widows, who bring me very old molds asking if I can reproduce
the piece within.
Not really sure what the mold is made of, i.e. what kind of plaster, or the
previous clay that was used, I've made a habit of soaking the mold in
water, and sponging all surfaces, as a good first step. (and then allowing=
to
dry of course)
As water is fairly non-corrosive I figure I can do no harm.
If, after soaking and sponging, I still find the mold uncooperative, I then
consider recasting it.
As well, I use Murphy's Oils Soap, as a separator, in the mold making
process. I suppose you could lather it up and try to dissolve the surface
contamination, and then soak it in water to thoroughly clean it, but I've =
never
used Murphy's in that way before.
a side note: have you ever thought of wetting your molds before each pour?
Years ago a porcelain doll artist explained to me that she likes to soak
her molds before casting. I'm working with a cone 6 porcelain that likes t=
o
stick. I too have started to soak my molds before pouring and find it real=
ly
works wonders.
Perhaps others on the list have more on point recommendations?
take care
Jeff Longtin
Minneapolis
_www.jefflongtin.etsy.com_ (http://www.jefflongtin.etsy.com)
Snail Scott on tue 13 mar 12
On Mar 13, 2012, at 6:52 AM, plasterjfl@aol.com wrote:
> ... have you ever thought of wetting your molds before each pour?
I have also found that although a saturated mold is of
no use, a too-dry mold does not properly wick the water
away from the slip. Doesn't take much water to 'prime' it,
though, and I've never had clay stick to the mold if it's too
dry.
I wonder, if the mold has become clogged with too many
salts (from hard water or deflocculants) if it might cause
Liselot's symptoms. A clogged mold can have trouble
wicking the moisture away from the slip and consequently
may cause some difficulty in releasing, though I've never
had trouble at the level described.
Jeff's suggestion of re-casting the mold may be best, though
it will be a fair amount of work. Work soap well into all the
mold surfaces, cast plaster into the cavity t fill it, then remove
one mold part at a time to re-cast it in fresh plaster. Don't
forget to soap the surfaces of the fresh casting wherever
they are exposed!
-Snail
-Snail
plasterjfl@AOL.COM on tue 13 mar 12
Hey Snail,
I'll explain a few things in detail.
For the last 12 years, or so, I've been casting plates and platters with
two part molds. One part has texture and forms the topside of the plate
while the other part forms the bottom of the plate. (The foot rim in other
words.)
The rim of the plate is cast between the two surfaces of the molds. Since
switching to a porcelain clay last year I've been having circular cracks
occur, in the casting process, around the perimeter of the plate well.
As best as I can surmise the clay is "catching" between these two plaster
surfaces. (If I cast the topside mold part independent of the bottom mold
part I don't have any cracking.)
If I soak the topside mold part in water, before binding the two mold
parts together, the casting comes out without this circular cracking. (Whi=
le I
don't find it necessary to wet the mold in most casting situations I did
find it useful in this one.)
saturation: for the sake of this discussion I'm distinguishing between
"wetting" the mold, with water, as opposed to a "saturated" mold. If I rec=
all
USG suggests that a mold be thoroughly wetted before use. They say this
allows the pores of the plaster to be "opened". (Once the mold dries.) A
"saturated" mold, a mold in which three or four casting have been made,
consecutively, does become unusable and needs to be allowed to dry before =
further
use.
The chemistry people can speak to this better than I but I find a mold
wetted with drinkable water doesn't really affect the casting process as m=
uch
as a mold saturated with sodium silicate laden water. (But I might be
wrong?)
btw - What I've written above is separate from my advice to Liselot. I was
suggesting wetting the mold, while brushing with a sponge, to allow the
evaporation process to further remove any contaminate in the mold surface.
take care
Jeff Longtin
Minneapolis
_www.jefflongtin.etsy.com_ (http://www.jefflongtin.etsy.com)
Jeff Lawrence on tue 13 mar 12
Hello Liselot,
Plaster molds work poorly if the pores (the tiny gaps that suck out
the water) are blocked, usually by some type of oil or soap.
If this is the problem, you can probably fix it temporarily by wiping
the mold surface with isopropyl alcohol on a soft cloth (don't use
paper towels - they are abrasive and will ruin your detail). However,
the problem will return if the pulp you use contains any residual oil.
Also, if you mix your own slip, be careful you don't use too much
deflocculant (sodium silicate, soda ash or Darvan). That can also
cause problems with absorption (not to mention making your molds turn
yellow and sprout ugly gray hair on the outside ...)
Good luck,
Jeff
| |
|
