26th ENTRY - Moulds in the Future

Note to Self

My design of the join in the upper arms of the puppets, allowing for the arm and hand to be replaced, was not very successful. I knew it would be impossible to achieve a perfect join in this way, but at the time it was the best solution I could think of.

 

After experiencing the mould-making process as well as silicone as a material, I have come up with a new solution for the future.

Maintain the sculpture intact. Make three moulds at once - Mould 1 for body, Mould 2 and 3 in a second step for arms with hands.

In step 1, make the bed and walls for the figure, with a clay wall cutting off the arms.

Step 2, clean away the clay wall separating the arm to reveal the resin from the body mould made in step 1.

Make a guide in the upper arm, lower down than the mould wall, which will be the cut line for replacing an arm. This guideline should be made into the sculpture as well as into the mould bed (see bottom of the page in Fig. 1).

This should give three moulds. It will probably be a positive thing to have a separate mould for each arm, as rarely will both hands need to be replaced at the same time, and it is confusing to know which part of the two halves of a mould correspond during casting when there are two separate elements in the mould and one only wants to cast one.

With this method, during casting of a replacement hand the upper arm will fit into the hand mould and the cast will adhere to it directly in this stage, instead of requiring a joining stage post casting (Fig. 2).

Note: It may be a good idea to devise a way to fix the three moulds together for the first complete casting, though perhaps not important.

Fig. 1

Fig. 2

Also, feet have been problematic in the mould-making process, as well as in the casting phase, because of their vertical position. 

Feet should next time be either spread out sideways, or, and probably preferably, in order to avoid twisting leg muscles, pointing straight down as a ballet position.

As Tobias has not yet finished sculpting Mr. Bernard, I may suggest that he try this approach.

TEST

Entry: Wednesday October 3rd, 2012

Before making the new mould from the re-sculpted Isolde, I decided it was important to test the above theory.

I used the silicone "dress mannequin" cast from the original Isolde for this test. The fact that this figure was a thick silicone cast made moulding her a bit tricky, as she tended to move around a bit, and her thumb popped out of the first half of the resin mould (the bed).

But, although it was a very crude test, I believe it was successful.

Before the test, however, I did succumb to a nostalgic weakness, and took the bus to Kingston to enjoy some moments in a toy shop, surrounded by Lego.

I cannot claim it as my own idea to use Lego blocks for mould-making walls, but they are wonderfully therapeutic, and do the job quite nicely. Fascinating how much fun they still are.

Figure resting face down. Water based clay built up for her resin back part of the mould (which I refer to as bed).
I brought the clay quite high up, making deep undercuts, as she will be cast in rubber, and for the arm replacement process, the bed needs to be shallow enough for her to lay in it easily.

Resin poured for mould back

In the first step, I made two little notches in the clay, following the cut seam line in the arm. These will be a guide for cutting the arm off, and for lining it up in the mould.
Here above I separated the arm with a clay wall. I used two toothpicks sticking through the clay wall which would be embedded into the resin, and act as forks to hold together the two parts of the upper mould. In the proper mould I will use steel pins, probably hex keys.

Second part poured, after removing the clay wall.
This picture was taken after everything had cured and I had removed the Lego walls.

Before pouring the two top parts of the mould, I laid down strips of clay to leave trenches. These will allow excess silicone to escape during casting, without blocking the mould from closing tightly.

A new silicone cast from this mould. The arm looks messy because the original was so, from my previous bad method of joining arm to body.
However, the cut line was visible, making it easy to cut off the arm using the guideline. The arm came off a la Terminator II.

Figure laying in bed, with bare armature arm in place for new skin.

Casting new arm

New arm cast directly to the figure. first arm above.
The experiment was successful.