Moulding
Through this workshop I learnt how to produce a single cast in plaster.
For a fragment, the most common option would be to either cast the front or the back, but I was really keen on trying a profile (with a challenge around the arm).
General process:
We have made a sculpture in clay (the original, positive).
We want to create a plaster mould from it (a negative).
Once it's dry, we get rid of our original to access the mould.
After being cleaned and protected by a waxy layer of soft soap, we pour plaster in the mould to create our cast (positive).
Waiting for it to dry, then chiselling off the mould (therefore a single use) to access the cast.
This is only how I understood and remembered it, I'm by no means an expert on the matter but hopefully this will be of some interest :)
Day 1: creating the mould
Delineating the fragment by building a wall (the golden shims inserted all around).
Starting the mould with a first layer of plaster. To prevent air bubbles to form, this layer is applied by flicking as well as using straws to blow the plaster in the smallest creases.
Applying a tinted layer of plaster. This way it'll be easier to see the limit between mould and cast when we'll chisel the mould..
More plaster, layer by layer, to fill holes and to even out the surface.
Applying hessian strips in two layers to add rigidity to the mould. One applied vertically, the other one horizontally which will be easier to peel off when we'll start breaking the mould.
Letting it dry overnight.
Day 2: cleaning the mould and creating the cast.
Digging the clay out and pulling the armature off to free the mould.
Making sure not to scratch the mould: any unintentional scratch in our negative mould will appear as a spike on the positive cast.
Running water to soften and brush off the last bits of clay. (on mine, the arm was particularly difficult to access and clean).
Using soft soap to finish cleaning and to build a waxy layer that will isolate the cast from the mould.
Letting dry over lunch break
Now starting the plaster cast. The first layer being super important as it's the one that will be visible: it needs to be thin and even, no air bubbles.
Making it sturdier by adding some wire and hessian strips.
Adding hanging accessories. If the bits of metal we're using here aren't galvanised, they could rust and dye the plaster. Treat accordingly.
Adding the last layers of plaster, aiming to keep the edges thin for aesthetic, and in the same time thick enough not to be too brittle.
Letting dry overnight.
Day 3 (only a morning) : breaking the mould to reveal the cast.
Peeling off the hessian strips (remember horizontal and vertical layers made this step easier)
Chiselling off the mould, starting along the wall.
Slowing down when reaching the pink layer, which means we're getting close to the cast.
Later: fixing once everything is fully dry
Pouring glue in the cracks (arm).
Adding bits of plaster where I chopped too much off
Sanding down a few undesired bits and cleaning the edges.
Et voilà !
I'm really glad I got to try moulding: beyond the challenges (easy to go wrong at any step and ruin the whole thing) there's something quite magical once you reach the 'big reveal'.
It also demonstrated why paying someone else to do it costs what it does: it is a tough job that can't be hurried and each piece has individual constraints.
I'm now looking forward to the new term, where I'll be learning different ways of casting, this time directly on the human body.
So… more 3diness to come!