traditional bronze cast sculpture, solid ones, are
expensive. The British firm of Alex Tiranti in 1959
developed a cold casting process to achieve the same
looking result as a furnace produced article, at a
fraction of the cost. The process consisted of coating
the inside of a rubber mould with a metal filled gel
coat of resin and then backing up or completely filling
the mould with a resin containing a lower cost filler.
What Metals to use
Although bronze metal flake powders are often used
to give coloured effects to resin castings, a true
metal powder must be used to give a realistic metal
cast effect in cold casting.
Among the metals
used in this process are Bronze, aluminium, copper, brass
and iron usually of a 200 to 300 mesh size in irregular shaped
particles (not flake). These metal powders can be obtained
from us by clicking
These metals can be treated with chemical patina solutions
to give true aged metal appearance. Being actual metals, colours
will vary from batch to batch due to oxidation, so sufficient
should be purchased to complete a particular cold casting
How much metal is required?
The resin/metal mix should be as high as possible. Too little
metal will give a very plastic appearance. An ideal metal
to resin ration would be equal parts by volume. We add slightly
more metal filler to make sure we have enough to yield a mix
that is still pourable or brushable.
The temperature of your working area is very important. At
lower temperatures the resin mix takes longer to go off ad
is much thicker than usual and so will not accept as much
The usual amount of catalyst to be used with cold casting
resins is 2 to 3% except with aluminium which usually only
requires 1 to 2%.
Warning: Safety requirements
Always wear a face mask to prevent the inhalation of dust
from the metal fillers. Aluminium powder can form dust clouds
when being used which can form an explosive mix. Aluminium
can also have a dangerous interaction with water. Always mix
the resin with the catalyst first before adding the metal
powder as the metal can react with the liquid hardener if
What colours are possible
Metal fillers can be mixed together to give colour variations.
A lifeless bronze can be given a brighter look by adding a
little copper. In reverse, a too striking copper can be toned
down by adding a little bronze.
type of mould to use
Your bust mould may be made from any one of a number
of rubbers or plaster. Silicone is highly recommended
if you are going to make many cold castings from the
same mould. Polyurethane is suitable for most uses,
while plaster can be used for rigid articles with
no undercuts. Latex is not suitable for metal/resin
castings as it is not compatible with brass, bronze
or copper, however it is fine for short run cold castings.
Your mould may be a one or two piece mould. If it
is a plaster mould it should be completely dry. One
coat of Release agent should be applied and let dry.
Silicone moulds do not need a release agent. Polyurethane
moulds should have the appropriate release agent applied.
We recommend using our CraftSil
General Purpose Silicone.
much metal to how much resin
The use of a clear casting resin is recommended as
the resin colour affects the final outcome. It is
important to use sufficient metal powder to give a
truly metallic appearance to the final product. Too
little metal and you will lose the metallic look or
the metal will settle to the bottom of the mould.
This especially noticeable with low viscosity polyurethane
resins such as CraftCast. On the other hand too much
metal is costly without adding the metallic effect.
Regardless of which metal is used , the minimum amount
of metal powder that can be used effectively is one
part of metal powder to two parts of resin by volume.
For a lot of our cold casting work we use equal parts
of metal and resin by volume to produce a result that
is indistinguishable from an actual metal article.
We suggest that you experiment to determine the ratio
of metal to resin that gives you the finished product
that you require.
How to Mix
Stir the catalyst and resin together in a disposable paper
cup using a wooden stirrer or tongue depressor. Then add the
metal powder and stir till thoroughly mixed.
How to pour your mould
This mixture is then poured into the one-piece mould to yield
a thickness of about 10-20mm thickness. This is achieved by
placing a piece of laminated wood coated with mould release
over the opening in the base of the mould after the resin/metal
mixture has been poured into the mould, and then rotating
the mould in all direction to ensure adequate coverage of
the inner mould surface.
After 1 to 4 hours, when the bronze face coat is leathery,
but has not yet hardened a low cost backup material can be
poured into the mould to fill it. This can take many forms,
from a silica filled resin, polyurethane foam, plaster, cement
or iron loaded resin for weight. Another method would be to
back up the bronze face coat with fibre glass and resin toe
yield a lightweight but very strong bronze faced cold casting.
When cured, demould and rub the surface with steel wool to
bring up the highlights. Patina may be added with a black
or dark oil based spray or brush on paint. Rub off the high
spots with a cloth, leaving the paint in the texture and when
it has dried, burnish with steel wool and wax if desired.
You can purchase
Powders and Resins
for cold casting on our online Mould store by clicking