Frank Colson on fri 29 apr 05
Plaster is, for the most part, one of the basic materials used by a large
majority of clay artists. But, is plaster, is plaster, plaster? No!
Plaster is a gypsum product but it can come in many grades! Most commonly
known is Plaster of Paris, and next, Molding Plaster, because it can be
acquire at nearly any builder's supply outlet. Also, well known, is
Hydrocal. Hydrocal can be a great asset for making molds and forms because
it is super strong. Many a time I have made 24" wide Hydrocal bats upon
which I could throw 25 to 26" wide platters. I used the metal lid of a 55
gallon drum as a form to cast the bats.
After Hydrocal, which is also readidly available, is "Ultracal" which puts
Hydrocal to shame. This is a little more difficult to acquire as it is
not readidly kept in stock with large plaster suppliers. Also, if you have
a need for a really strong plaster, you might just as well stay with
Hydrocal as bother to special order Ultracal.
By the way, Hydrocal is widely used in the medical field. You can go to a
medical supply store, purchase Hydrocal laced gauze by the roll.
I have use this to make a "body cast" directly applied onto bear flesh.
Its makeup is totally harmless to the skin.
Next on the plaster higharchy for strength is "Hydrostone". Now, our way of
thinking needs to change with the use of this gypsum base
material. A great example for using Hydrostone is the ability for casting
white marble sculpture. Why go through all the labor intensive
effort to carve a sculpture out of a block of marble when the original
prototype piece can first be made in clay? After making a plaster
negitive piece mold of the original work, simply pour in a solid mixture of
50/50 Hydrostone, and white marble powder. The head of a sculpture art
department at a university, where I was on staff, used this technique as his
sole medium of expression. After the cast is set up, only the seam lines
need removing once the piece mold is removed. It is virtually impossible to
tell the difference from a cast marble to a carved marble sculpture if good
craftsmenship is used.
Mixing gypsum plasters is something else. There seems to be several
approaches. I will not attempt to address this issue presently.
I will say, however; if you wish to accelerate the set up time, use warm or
even hot water! If you want to slow down the initial set up
time, use vinegar in your water.
Frank Colson
www.R2D2u.com
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