Tuesday, 16 April 2013

Oh Well- puppet construction part 3

Part 1
Part 2

Walter's legs

The fourth and last mould (legs) was by far the most complicated. I chose to create both legs, though separate, in the same mould so that I could conserve its size. The two legs could still be filled independently.

Much like the hands, I drew a basic footprint on paper, and used this as a stencil to create two identical (albeit mirrored) soles. The leg armatures were placed upon these soles, with the top of the feet bulked out on top.

Once again, a relatively simple two-part method was used to create the leg mould- the difficulty came in removing the sculpt from the completed mould later on. 

The first half of my mould covered the entire upper leg. The sculpt had to be unfortunately destroyed for the armature to be removed once the plaster parts were complete, since the knee joint would not fit through the ankle. To remove it, I scooped out the Plasticine foot and unscrewed the ankle joint, pulling that out the bottom and the leg armature out the other end. This was necessary in order to split the mould in two however, allowing the cast models to be removed later.

When creating the second half, which would cast the soles of his feet, it was important to have the tie-down screws in place, so the holes will remain open on the cast models.


NOTE: to any readers wishing to follow this guide, I strongly advise reading on before attempting any casting. I encountered numerous problems and ultimately did not use the latex technique detailed first. All problems and appropriate solutions are covered further below! 

With my moulds complete, I was ready to prepare my armature for casting my puppet components. I padded out the armature with foam, aiming to add a constant barrier between the latex and the brass (with which it is slightly reactive- a barrier should negate any negative effects, I was told). 

With no prior experience casting with latex, I practiced with a test hand to familiarise myself with the material somewhat. I was surprised that the latex mix remained cream colour despite having added a decent amount of brown paint. I had expected the mix to become the desired colour before applying it to my mould, but discovered that the colour in fact changes as it dries to match the paint. One mistake I made was watering down my paint, making the mix quite runny. This it turns out also greatly increased the shrinkage of the cast whilst drying, resulting in a somewhat flat hand with a messy surface texture.

The two hand mould halves were filled separately. Once the mix was tacky and able to hold its shape for a few seconds, I placed the wire armature on top of the latex and clamped the two halves shut. This had to be done quickly to stop the latex from dripping out.

Learning from my mistakes, I mixed a second cupful of latex adjusting the colour to more closely resemble my character design and making sure not to add any water! This time, I proceeded to fill all of my moulds. After waiting overnight, I removed the casts.

These next bits are fairly wordy, but they're of critical importance if you want to follow this guide for yourself! Read on to find out exactly what will and will not work with different casting materials. I was very close to losing several weeks worth of work here!

Problem 1- The Capri-Sun effect

My first impressions were great- the moulds had worked like a charm, able to replicate my original sculpts as accurately as I had hoped for. After waiting a couple days further however, it became apparent that only the latex on the surface was dry. Despite having left considerable air channels in my moulds, the surface latex had dried first and very quickly sealed everything else within, essentially leaving me with some squishy bags of liquid. Cue panic.

After bouncing ideas around with industry professionals, the general consensus seemed to recommend using silicone instead, which sets via chemical reaction and is not therefore dependent on air to cure. Furthermore, it does not shrink as it dries. Colour is also added via a consistent pigment, meaning there is no colour discrepancy between casts as could arise from trying to mix the same colour with acrylic (to mix with latex).

Time was the real problem here as I was being pushed further and further away from my schedule. Bentley Advanced Materials came highly recommended for purchasing silicone, and I was able to arrange a visit to get the opinions and assistance of the very friendly and helpful staff. Unfortunately, I had to cut the dry latex from my armature, wipe off the liquid latex, remove the ruined foam (latex and silicone react) and re-pad my armature in preparation for the silicone.

Problem 2- the latex has the last laugh

Thanks to the staff at Bentley Advanced Materials, I was able to learn the basics of mixing and applying silicone. The cure time for the product I purchased was around 5 hours, and upon returning home I left extra time to be sure the silicone had set prior to opening the moulds. On later inspection however, for some reason the silicone was sticky.

Waiting overnight did not solve the problem- the silicone on the surface had clearly suffered inhibition preventing it from curing. As I have since learnt, liquid latex contains ammonia. It sets when the moisture evaporates, and the ammonia is absorbed into a porous material- in this case, the plaster of my moulds. You can guess where this is going- the silicone had reacted with the ammonia/latex residue that now permeated my moulds, causing it not to cure.

After contacting Bentley again, they recommended that I seal my moulds with several coats of PVA glue in an attempt to prevent the ammonia from leaching into the silicone again. This took the better part of a day, and I had to clean up and re-pad my armature once more before driving back to Bentley Advanced Materials for another attempt at casting my puppet.


Along with the PVA-coated moulds, the staff suggested using an accelerant chemical to speed up the cure time of the silicone, so that it would not be in contact with the moulds as long in the hopes of reducing the chance of inhibition.

This time, I was very relieved to find that everything worked perfectly! All in all, I am incredibly grateful for all the help I received in overcoming the problems I had faced, and would most certainly recommend Bentley Advanced Materials to anyone interested in casting models.

By this point, I was running a good fortnight behind my schedule, eating into my time originally allotted for animating. I still needed to trim the excess from the casts and assemble the puppet, complete with finishing touches.

The lessons learnt here were valuable and will undoubtedly be useful in the future. It seems imperative to be certain before casting what material you will use. Regular liquid rubber latex is not suitable for anything thicker than 5mm it seems.

There is the added question of reactivity too. I would advise anyone to thoroughly research materials and what they can be used with before attempting any casting.

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