SNUURG'S LITTLE WORKSHOP
... thought I'd do one of them 'how I did it' kind of things relative to some of the various works I've produced over time, primarily regarding the sculptures and castings I made while going through my Crittercraft phase - wherein I created maybe sixty or so different wildlife subjects - whether birds, frogs, mice, or other animals, at various sizes usually according to the animals' actual dimensions, or very occasionally at smaller scale where the subject concerned would be too large for life-sized replication.
To help out, I've bashed together a quick set of pictures that follow the process involved in making moulds and castings of an original figure: wherever I've mentioned any of the particular materials I might have employed in the part of the process being described, I have also included a link - with the word concerned shown highlighted - that will take you to a list of the suppliers I tend to use most often when ordering my materials.
The following text describes one of the most elementary forms of moulding and casting, using a re-meltable moulding-rubber known originally as vinamold but now more commonly known as gelflex : the method works equally well - or rather, somewhat better, with any of the various silicone rubber compounds, but at the time I needed to use the cheapest materials available, hence the re-usable vinamold rubber.
The first image shows the original sculpture prior to any part of the moulding process: the piece is sculpted from plasticene built over an armature, worked and detailed to the desired finish, or perhaps to a point slightly less than finished - the moulding process tends to cause some degree of damage to the original before the actual moulding takes place, so I usually leave the piece with still a little work needing to be done, such that any fixing-up becomes part of the finishing work before making the mould.
The next stage is the initial preparation for moulding: the sculpt is wrapped in cling-film / cyran wrap or equivalent to protect it from the worst of the process; the whole work is then encased in a layer 10 to 15mm thick of either clay or plasticene ( the piece shown in cut-away here to show what's going on ), with 'risers' built onto the mass to provide pouring access for the rubber and to allow some 'escape' of the vinamold - this will be explained later.
Image two shows part of the 'plaster jacket' built around the mass - I usually execute these in two or more pieces to make the mould more accessible: build up a thin wall of plasticene running across the main body of the mass: then, using a very thick mix, quickly build up a layer of plaster over the newly-sectioned mass and up against this wall: once the first mix has set, remove the plasticene dividing wall, and apply a release agent to the exposed parts of the plaster before applying the next part of the jacket. Repeat until all necessary parts of the jacket are made and the whole mass is encased.
Once the jacket has thoroughly dried, remove each section from the mass and then peel away the mass from the underlying sculpture: looking at the next picture shows how the jacket now houses a cavity between itself and the sculpt - this will be taken up by the vinamold when it is poured.
Fix the entire jacket back in place over the sculpt, after finishing any necessary work to the piece itself: seal any gaps in the jacket but leave the pouring-hole and the riser-spaces open - when the rubber is poured, the riser-holes will allow some of the material to 'escape', ensuring that no air can be trapped inside the jacket, and making sure the mould fills completely with rubber.
When the rubber has fully cooled, take the mould out of the jacket - the rubber should have assumed the shape previously made by the mass of plasticene. Depending on the complexity of the sculpture, you may or may not have to perform a little 'surgery' to extract the sculpt from the mould, but careful work with a scalpel or sharp craft knife will ensure a neatly-fitting empty mould ready for casting. The picture here has the sculpt in cut-away again, showing how the vinamold has taken up the space left by the plasticene mass.
Using whichever casting material you prefer, carefully fill the mould and allow the material to harden: vinamold works well with most plasters and casting resins, but the use of even low-melt metals would not be advisable as they would be likely to damage the mould: once again, silicone rubbers of several sorts would be more appropriate for such requirements. Picture (5) shows the first cast from this mould - as you can see it is far from ideal, requiring some degree of filling and finishing before it will be ready for painting.
The next image shows the cast piece after just such ministrations have been made: I tend to prefer milliput - a two-part epoxy-putty - for my filling needs, it adheres to almost anything and works well with just about any sort of sculpting tool, even my home-made ones.
Once filled and finished, apply the base colours for the subject concerned, and then work up from there with various shading and highlighting techniques until the required degree of finish is achieved for the completed model. I generally use enamel paints, or sometimes acrylics.
There are a couple of variations on this moulding-method that I perhaps ought to cover too, as it's always possible you might get better results with a different way of approaching the same problem: the first of these is the basic two-part mould, which is particulaly suitable for items that are essentially 'two-sided', i.e. not too complex in structure, such that you can effectively make a maould of each half of the piece and fit them together quite neatly. For an example here I've used a small skull and a couple of horns that I've been moulding for another figure.
Basically, the parts concerned should be embedded to about half their depth into some soft medium such as plasticene, uncured sculpey, or whatever suits your purpose. The medium should be pressed up against the sides of the chosen object to create a neat seam around the piece that'll prevent any rubber 'escaping' around the sides of the piece when it is covered.
Next, build a wall of plasticene or milliput around the embedded eobject(s) of a sufficient height to make sure the entire half-piece will be covered over when the resulting enclosure is filled with rubber. Use whatever moulding-compound you prefer, and allow to cure.
Removing the embedding medium from the back of the mould, the wall should now be extended from the back of the moulded piece to create a second enclosure around the reverse half of the work. Pour the rubber as before, allow to cure, and then remove the piece from the now-complete mould, ready for use to create castings. You can cut pouring-vents or runners into the rubber to facilitate entry of the resin or whatever other casting-medium you're going to use: I would recommend doing this in the uppermost surface of the first half of the mould so that the weight of the rubber holds the mould closed to prevent leakage, rather than trying to hold the mould closed in a more upright position opposing the seam of the mould itself.
Another method is the solid mould, in which a piece is entirely encased in rubber and then cut out once cured - this in theory creates a 'perfect' join of the mould-pieces, but is not always a reliable means of getting a good mould or casting. It is illustrated here with this simple box built around the piece being moulded - constructed here from plastic, with a couple of perspex walls that allow you to see what I'm describing: the object to be moulded should be supported inside the box in such a way that it is effectively 'floating' above the box-bottom - since we're requiring the rubber to completely encase the subject, it can't be allowed to touch the bottom surface of the mould-case; to achieve this, the piece should be elevated by rods of whatever substance is suitable (I've simply used fingers of plasticene here) to allow sufficient passage of rubber beneath the piece to create a functional mould. Once the rubber is cured, the work is cut out of the rubber, and the rods removed - the cavities left by these then form the vents and runners for the pouring of your casting medium. The mould should be taped or otherwise held closed to prevent leakages.
Take a look through my Crittercraft Galleries to see some of the other works produced using this process. For a little further information on how I create some of my non-reproducible works, take a look at some of the works in progress.
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