Jeff Lawrence on sun 5 jan 97
Susan Stern writes:
>And finally, I have been attempting to slip cast a pilsner glass and I'm
>having a lot of trouble. I made the mold in plaster last year, purchased
>porcelain slip and cast 4 with no trouble at all. Now that I want to make
>more of them (with that same batch of slip), they will not dry properly.
> I've moved them all over the house and even tried to cast them in a
>different venue to see if that would help. My house is not humid (on the
>contrary, it's quite dry) and I've poured them on the thin side but even days
>later, they will not come off the mold and are still flexible and tear. I'd
>really appreciate any help with this that I can get because I'd really like
>to cast several more of these soon.
>
Hi Susie,
If specific gravity is higher than 1.78,
add a little water.
Else if specific gravity is less than 1.78,
BAILOUT is indicated.
If BAILOUT is not indicated, then /* check deflocculation */
/* Slip viscosity goes up as it ages, and results in weak, flabby casts, which
which might be your slip's difficulty. I know the feeling, as my own
resistance to flow is increasing with age, too. Just hope I can
stave off the weak and flabby part for a while. */
While viscosity is high
if you already added a bunch of deflocculant,
then BAILOUT is indicated once more.
else
add a little more sodium silicate
/* A 100cc veterinarian syringe is a good and
cheap tool for this. */
/* use 1:1 Sod.Silicate and water solution; test
with a viscosity cup. Check with
your supplier on what time they look for.
Overdeflocculation is a trap easy to
fall into and results in long casting times and
casts sticking to the molds */
If BAILOUT is indicated
heave large sigh and go get fresh slip.
/* set the bucket aside until you have large vats of slip to
fold it into in small doses */
else
set all systems GO
/* If the slip is expensive, I think Chappell has a number of porcelain slip
recipes in his book for several temperatures.
This leaves hanging the larger question: does pilsner belong in porcelain? */
Jeff Lawrence
jml@sundagger.com
Sun Dagger Design
ph/fax: 505-753-5913
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