Art and Design A comprehensive guide for creative artists - Aaltodoc

Rich(1998, 250) offers a reasonable explanation: “A study of
Michelangelo's nearly finished stone carvings show that
he worked in a manner similar to Greeks and did not make
much use of the flat chisel, proceeding from the use of
the claw chisel to finishing stone abrasives.” Here we see
that stone especially Marble was a common material for
sculptors like Michelangelo, which was very hard for them
to finish it.
Casting clay
As Rich (1988, 39) reminds us, “There are two major methods
of casting with earthly clay; 1. Pressing or squeezing clay
into moulds, or hand forming against a mould. 2. Slip
casting. Earth-clay or terra cotta can be employed as a
positive casting material and cast it in sectional plaster
moulds when more than one copy of terra cotta is desired.”
Clearly, then, casting necessitates a mould—made up of
two parts or more—known as a positive and a negative.
Where by, the part with a hollow cavity is its negative and
the positive part is the place where a desired sculpture
forms by using hot molten (metal, glass) or wet slip made
out of clay.
Types of moulds
By simple explanation a mould is a reverse form of a cast.
It uses a hollow space to reproduce a resembling shape of
the original using liquefied substances that will later harden
to form a required shape. The solid materials of clay slip or
molten cools from inside a mould, it turns hard by setting to
form an assumed shape.
Here are some types of moulds:
Slip mould
In Segal's (1991, 28) Ceramic Fabrication,
“slip casting is a technique which involves
pouring a slip into a porous mould often
made from plaster of Paris (calcium sulphate
hemihydrate), it absorbs liquids and
deposits a solid material at the mould walls.”
It should be tied well to avoid falling apart.
At certain intervals the mould containing
slip is shaken carefully for a slip membrane
(inside) to fortify well onto a mould surface.
Then, residual slip can be poured out as the
shaped artwork drains to form a precise
shape with adequate thickness.
Gelatine mould
(glue mould)
Piece mould
Press mould
This type of mould is not very strong, but it
is good for reproducing small and detailed
sculpture artworks. Creative sculptors who
make artworks with a gelatine moulds use
glue, water and glycerine. Rich (1988, 101)
explains, “a gelatine mould is occasionally
referred to as a glue mould, but glue is
actually an impure and cheaper form of
a gelatine and does not possess as much
elasticity.”
As Rich (1988, 265) has remarked, “a piece
mould is a negative mould ... made with
several piece sections. The number of
sections to be made are determined by
under cuts of the artwork meant to be
cast,” and its sections are shaped in such a
way that; they are easy to remove “without
fracturing” the positive cast. This type of
mould is constructed in separate halves
and where necessary a mould created can
again be reassembled for another cast
reproduction.
On a press mould, the action and process is
done by pressing a prototype of the exact
sculpture artwork into a wet lump of clay or
a similar material—by applying pressure on
it. The generated negative shape or space is
later on used to cast another exact sculpture
artwork. A press mould can be used to make
a large number of individual press-cast
pieces. Peterson et al. (2003, 97) remark,
“laying a slab of clay over a plaster form or
pressing clay between a plaster moulds is
also possible.” Certainly, a press mould is
typically used for casting low reliefs.
A slip-cast.
Liquid clay was
poured into a
Plaster of Paris
mould. It absorbs
water from the
clay slip, leaving
a layer of clay
against the surface
of the mould.
198 199
Clay cast
Plaster of Paris
molds