Jeff Longtin on sun 8 apr 12
An opportunity has come up for me to start doing belly casts of expecting
moms.
Rather than use plaster gauze I'm thinking of using alginate. (Backed with
a plaster/gauze mother mold?)
I'm wondering if anyone has made such casts and what material they liked
best.
Thanks
Jeff Longtin
Minneapolis
_www.jefflongtin.com_ (http://www.jefflongtin.com)
Eve Rose on sun 8 apr 12
When I took Theatre Makeup in college, the alginate was more comfortable
than the gauze against the skin. Plaster would irritate and could get
too hot to be comfortable.
Jeff Longtin wrote:
>An opportunity has come up for me to start doing belly casts of expecting
>moms.
>
>Rather than use plaster gauze I'm thinking of using alginate. (Backed with
>a plaster/gauze mother mold?)
>
>I'm wondering if anyone has made such casts and what material they liked
>best.
>
>Thanks
>
>Jeff Longtin
>Minneapolis
>_www.jefflongtin.com_ (http://www.jefflongtin.com)
>
>
>
>
Snail Scott on sun 8 apr 12
On Apr 8, 2012, at 6:17 AM, Jeff Longtin wrote:
> An opportunity has come up for me to start doing belly casts of =3D
expecting
> moms. Rather than use plaster gauze I'm thinking of using alginate. =3D
(Backed with
> a plaster/gauze mother mold?)
Alginate is very floppy unless it's quite thick in=3D20
proportion to the mold's area, so a backer or=3D20
mother mold of some sort is essential. Alginate =3D20
feels very nice on the skin, unlike plaster, but=3D20
two considerations that would probably make=3D20
me use plaster alone are the cost of alginate,=3D20
and the fast working time/pot life of the alginate.=3D20
If you need to use it over such a large surface=3D20
area, you should mix with fairly cool water to=3D20
retard the reaction, and work fast. Cost is a factor=3D20
that you'll have to consider on your own terms.=3D20
There are a few other considerations, though:
If you do decide to work with alginate, you'll need=3D20
to pull a positive from that mold within a day or so.=3D20
Even well-wrapped, it won't keep forever, and=3D20
alginate (which is mostly water) will start to distort=3D20
and shrivel as it dries out. If you can't cast the=3D20
finished object directly from alginate in a timely=3D20
fashion, you'll need to pull a new positive from it=3D20
instead, to use in making a fresh negative mold.=3D20
Because of the water content, alginate works well=3D20
for plaster or wax castings, but not for clay. The nice=3D20
thing about an all-plaster mold is that it keeps well=3D20
(offering schedule flexibility), and can be used to=3D20
make a direct clay impression by press-molding,=3D20
from which the clay will release easily. To make a clay=3D20
impression from an alginate mold, you will likely have=3D20
to make a fresh positive of plaster and then a new=3D20
negative mold (also of plaster) to form the clay. While=3D20
it's possible to use nonabsorbent materials to do=3D20
press-molding, I can't see a good way to form clay in=3D20
a mold that's actively wet. Alginate is also fragile, and=3D20
likely to tear apart under the force needed to press=3D20
even soft clay.=3D20
The only use I can see for alginate - if the final product=3D20
is intended to be clay - is as a preliminary step before=3D20
making a final mold out of plaster. Sometimes, as with=3D20
squirming children, it's the only way to get a clean and=3D20
detailed mold, but otherwise I'd just work in plaster=3D20
from the outset and skip the extra step.=3D20
-Snail
| |
|
