Eleanor Hendriks on fri 18 feb 05
I have been trolling the archives in search of a solution to a problem I
have been having in the initial stages of slip experimentation. I mixed up
various thicknesses of the Universal Slip that I found in the archives
-thank you! I have had good success brushing very thick slip over newspaper
stencils. Dipping thrown forms into thinner (a brush dragged though barely
leaves a wake) slips and trying some apple cider mocha tea, slip trailing
and feathering also with met with reasonable success. I run into problems
when I try to pour slip onto one side of slab built plates. The plates crack
and disintegrate into flat broken objects after sitting for about 20
minutes. Applying the slip when the plates are leatherhard -about to show
dry spots seems to work better than at the soft leatherhard stage but they
deform even if they don't crack. My understanding of the problem so far is
that my plates are getting too wet in the process. The thrown forms that I
dipped fared better (I believe) because it didn't take as long to get an
even coat of slip while the slab plates required pouring which takes longer.
I can't pour the slip if it is thicker and thinning requires more water
-which I don't want. So we now enter the arena of flocculation and
deflocculation!! Am I right in saying that I need to mix new slip using less
water and adding something like sodium silicate or Darvan to get a thinner
consistency. How does this affect the relationship between the slip coating
and any slip technique I add ontop (marbling, feathering etc) -do these
slips need to be the same mixture or can I use the just water version? -well
I'm sure I can -but how do they react with each other?
Thank you all!
Kate Johnson on sat 19 feb 05
This appears to be one of those "your mileage may vary" situations, but here
is what has worked best for me.
I run into problems
> when I try to pour slip onto one side of slab built plates. The plates
> and disintegrate into flat broken objects after sitting for about 20
> minutes. Applying the slip when the plates are leatherhard -about to show
> dry spots seems to work better than at the soft leatherhard stage but they
> deform even if they don't crack. My understanding of the problem so far is
> that my plates are getting too wet in the process.
I think you're right...mine work best with two different techniques.
If I do them in a plaster slump mold (must be plaster--the china, plastic,
or other molds don't have the same moisture wicking capabilities), I can add
the slip and marbling or other decoration almost immediately--no need to
wait till any stage of leather hard beyond what it took to make the molded
form itself (often quite moist, here). Everything appears to dry at almost
the same speed, and no problems with warping, cracking, deforming. I take
the plate, bowl, or platter out of the mold when it's uniformly firm, and it
stays that way.
If I work flat (slip decorating heavily before putting into a mold, as in
marbling or feathering) or use a mold other than plaster (so there's the
non-absorbent factor to deal with), I use a hair dryer to speed the drying
of the slip. No warping or cracking there, either. It may not be
traditional, but it works.
I HAVE run into serious problems leaving the wet, decorated slab flat for 20
minutes or so, as you say--mostly wet-cracks, with that technique, though
several here have said that works fine for them, so it may be the surface I
have the clay on. I want to find something better (MUCH better!) before I
try that again!
I've also had wet cracks form on the bottom of a molded, decorated form, if
my mold in non-absorbent. That can be avoided with the hair dryer, again,
or impeccable timing, keeping the rim damp with plastic wrap and unmolding
at the perfect time, then allowing the bottom to dry on a rack while keeping
the edges slowed down...the indomitable Snail Scott suggested that. Works
well, and is probably very traditional.
Let us know how flocculation/deflocculation works--that's a new area for me,
and just exploring the possibilities...