FROM
CONCEPT TO COMPLETION
A brief explanation of the process
involved in completing a commissioned sculpture
Recently, a friend asked me to produce a sculpture of his wife's
dog Penny, a pedigree "Pointer".
Penny is a pretty dog and we agreed that this would be non-exclusive
commission whereby the sculpture would be of this particular
dog and he would have the first casting but I would have the
right to sell this as a part of the range of products in my
Sales Gallery.
This is brief picture diary of the course of this commission
from concept to casting and hand painting the final product.
This piece was intended as a resin casting for hand painting
from the outset.
Before you start>>>
It is important to decide this early on what the final medium
will be as there are a number of differences both in sculpting
techniques and in mould making if you intend to produce a
hot or cold cast bronze as opposed to hand painted resin.
The first thing to do is to take as many pictures of the
subject as possible. If you cannot take them yourself you
need to rely on your client but be specific about the angles
and shots you need. I like to use a camcorder for this as
it gives you a good feel for the character of your subject,
which if you are lucky will get built into your work.
Next take as many dimensions as possible but definitely eye
centres, length of head, nose to 'stop', head width and so
on. In this case I decided that the sculpture would be to
a scale of half-life size. I used Photoshop to scale up a
few of the most relevant photo's to working size, I can then
use the measuring tool in photoshop for detailed dimensioning
around eyes and ears etcetera.
Taking the First Step
OK now to make a
practical start. Hopefully I've accurately visualised the
job in my head so I have a good idea what I need for the base
and armature. I will need a flat surface for the bottom of
the sculpture. Then because this will be cast in a vacuum
tank, I need to create a reservoir space for the excess resin
that will expand in the mould. Thirdly I need the base for
the plaster back-up or mother-mould that I will create around
my finished work. Finally I will set this on a work base.
The resultant armature and base ended up as below
The base for the mother mould will need some registration
points I will use upholstery nails for this later on. For
now I am anxious to start sculpting.
I use a fairly hard oil based wax/clay which needs to be
heated in an oven to make it soft enough to apply
Starting the Sculpture>>>>
After
every job, I recycle it by melting it down, removing any "foreign
bodies" and then pouring it into cup-cake moulds so that
I end up with a stock of cup cake sized pieces of clay for
future use. I've had this clay so long i can't remember where
it came from
Now it is starting to take shape but the ears are a bit incredible<
I like to use marbles or ball bearings for the eyes in the
original if the piece is to be hand painted. They make for
realistic reproduction but it is very important to get them
at the right height, depth and centres otherwise you can end
up with a figure that has eyes pointing in different directions,
up down or sideways and it is nearly impossible to correct
on the finished casting, even with painting.
I decided to make the short stand from neck to base, look
like a piece of driftwood, it seemed like a good idea at the
time and I couldn't think what else to do. It seemed to work
but this was destined to be changed on the final piece.
On to moulding. >>>>>>>>
If this was a bronze, I would need to do a two piece mould
so that a hollow wax could be painted into each side for lost
wax casting. However as this is for a resin reproduction,
the more joints or seams I have the more of a nuisance and
a disfigurement it will be so I am going for a single skin
silicon mould with minimal cut lines - in this case, just
one from base to under the chin. I will make the final cut
in the mould with a scalpel. Oops! I nearly forgot the registration
points for the mother-mould.
As you can see, I've incorporated a seam divider under the
chin in order to give me a guide when cutting mould at the
end. The rod coming down from the chin will also act as an
air release in the mould to avoid air bubbles becoming trapped.
WARNING: If your model is made with a soft
clay or is very intricate you need to make a "block mould"
before going to the next stage.If you do not you could damage
your original beyond reasonable repair.
A block mould would be the same process up to now except
at this point you would build a containment around your clay
original and simply fill it full of vacuumed silicon rubber.
You will get a perfect reproduction of your original but made
with a lot of expensive silicon. You will then need to use
a hard copy reproduction to go on to the next stage. Of course
if you only want one copy for yourself you can stop here.
Protecting your Sculpture>>>
As I am making a "skin mould", next I need to protect
the my original clay sculpture, I use kitchen foil but you
could use cling-film just as well. I like foil because there
will be some heat generated in forming the mother-mould and
I think the foil helps to reduce the effect on the surface.
First steps to create a Back-up or Mother mould>>>
I am now going to encase my protected original, in a skin
of wet clay in order to form the mother-mould. I use wet clay
because it is soft and forms over the original without the
need to exert any risky pressure which might cause damage
or movement.
I roll out the clay (like baking a cake) with depth guides
to maintain an even thickness and then lay it over the model
until I have fully encased the original
The pipe was intend as the main feed for pouring the silicon
but in the event, I used a different feed. However it was
not wasted as it formed a reference for the silicon and a
riser for any trapped air.
There are many ways to form the boxing for the mother-mould
and there are also a few alternative materials to use for
the purpose. This is just the way I did it for this figure.
In order to form two halves, I often use, as in this case,
plaster board. It is strong and easy to cut with a jig-saw.
Firstly mark out your work as accurately as you can and then
cut it out.
This is a little bit simplified but now the plaster board
needs to be fitted around the encased original and box shuttering
put in place to form the plaster.At this stage, you have to
hope your armature was strong enough for it not to collapse,
I usually support it underneath to help avoid that situation.
Any gaps around your work piece need to be filled bearing
in mind that you need to avoid undercuts or any awkward shapes
that might make casting difficult. Also because I've used
clay and it will stick to the plaster former I give it a liberal
coating of release agent made up of petroleum jelly and white
spirit. When I get around to taking the plaster back-up's
off later I don't want anything to catch and risk damaging
the original.
Applying the Plaster Case>>>>
I want my plaster mother mold to be as strong and lightweight
as possible. Also to avoid damage to my original work piece,
I want to minimise the heat generated during the plaster curing
process. For these reasons I will make a thin laminated mother-mould
using fibreglass strips to reinforce my plaster shell. I use
a plaster called Crystacal R and you can find more information
on it at www.bpbformula.com
My basic method is to pour a little plaster over the work
piece and then soak the strips of Fibreglass and lay them
over the top (pic.2) when I think I have enough on, I poke
and prod (pic.3) to try and remove any excess air from the
inside surface of the cast. As the plaster starts to harden
off, I then form it up at the front and back (top and bottom)
and smooth it off (pic.4)
Time to do side 2
This is essentially a repeat of side one. I need to make
registration keys in the plaster so that the two halves join
correctly and I use a countersink drill bit for this (pic.2)
I also need to use the release agent again on this side to
stop the plaster sticking together.
You then end up your completed mother-mould all the time
hoping of course, that your original artwork is intact inside.
We should wait 24 hours now for the plaster to harden and
cool off - I rarely have the patience for this as I start
to get a bit excited now I'm this close to the end
When you are ready prize apart, ever so carefully, the two
half of the mould and peel of the layer of clay. This is the
part where I hold my breath - it is inevitable that some surface
damage will have occurred but if you have been careful, this
should be minimal and easily cleaned up
Pouring the Silicon>>>
Before discarding the waste clay, I weigh it to give me a
rough idea of how much silicon I need to mix for the mould.
The inside surfaces of the plaster will need to be cleaned
and sealed before the final stage. Also air bubbles need to
be filled, I use epoxy putty for this. I would normally spray
paint the inside of the plaster cast with grey primer to complete
the sealing process and neaten up the mould but I haven't
got the time on this occasion. Before moving on, drill the
casings wherever it looks like you might have an air trap
or want to provide an escape route for air
To avoid the silicon sticking to the plaster surface when
it is moulded, I need to use release agent but I believe that
the silicon is affected by white spirit so I use a mix of
tap water and washing up liquid which works quite well. You
must be very careful when placing the plaster back-ups around
your original because any little dink or scrape will be forever
impressed upon your casting.
OK, all done and ready to pour the silicon rubber
It is essential that the silicon is de-gassed in a vacuum
tank so that all air is removed before it is poured into the
back-up plaster. Vacuum tanks are expensive items but the
cost can be reduced by buying second hand pumps and making
the actual tank yourself but that's another subject.
Ok I'm nearly at the end now. The sculpture is "under
rubber" as we say in the trade
Allowing 24 hours for cure, I now prize the two plaster sides
apart and reveal the silicon mould. First job is to clean
off the superfluous bits of rubber (being very careful not
to cut into the mould) so you end up with a mould as in pic.2.
Next having decided where the cut is going to be we just "confirm"
it with a good long and sharp blade. When I am happy that
I have cut in enough, I just peel off the silicon. A big surprise!
my original is almost perfectly intact, they usually get totally
destroyed at this stage
Taking the First Casting>>>>
I am now ready to cast my first reproduction and I cannot
wait to see the outcome. I will make up a mix of 50% polyester
casting resin and 50% white marble dust. I will then pour
it into the mould and put it in my vacuum tank to extract
all the air bubbles from the casting
In 'pic.1' you can see the reservoir area to avoid expanding
resin overflowing in the tank. In 'pic.2' I have inserted
a threaded rod mainly as reinforcement to stop the casting
from snapping at the weak points and also for fixing it down
onto the intended hardwood base. 'Pic.3' and I'm peeling off
the silicon and HERE IT IS 'pic.4' my first casting as good
as I could have hoped it would be.
The Finished Product>>>
The only thing left to do is paint it and fix it on a base
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