Now that I have one trial mould, I designated a studio area at home to start experimenting with different materials.
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| my home studio |
Some observations about the materials to be used for moulding and glass casting, will help me narrow down the search.
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| Polystyrene |
Polystyrene or the blue foam is an extremely lightweight; however it is also easily damaged and is very porous, which makes it less useful when high level of detail is required. It is compatible with 3D CNC Router Pacer, easily cut with handheld hacksaw and otherwise manipulated with various tools. The material is easily deformed when heat is applied, it does not have a melting point but burns instead, when the temperature reaches over 200 degrees Celsius. It is completely odourless and relatively cheap to obtain as a raw material. A sufficient amount of detail is achieved for smooth casting with silicon, wax, resin etc. My verdict was that I could not use this directly with glass, but rather create a negative for moulds.
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| Type B modelling wax (natural) |
Type B natural wax is a dense, odourless material with medium softness. It responses instantly to heat source, including the body warmth, making it ideal for hand sculpting and shaping. It melts gradually and feels very “alive” with a distinct character. This particular wax can be melted and reused many times as it carries the mould impressions very accurately and has an almost instant hardening time, when the temperature is cool enough. It is relatively inexpensive, considering the life span of the material, however the heat factor is prohibiting when it comes to slumping glass or even acrylics.
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| Lightweight modelling clay |
Fimo air- light professional modelling clay is incredibly lightweight, with 24 hour or less air drying time, depending on the complexity of the piece. It is odourless and easily manipulated by hands or other tools. When wet, it is non-sticky and when dried, it is non-reusable as one would expect from a standard clay. A piece crafted with fimo air does not have a high temperature tolerance. It is overall a very flexible and consistent material and has from moderate to high impression detailing. The colour is slightly off white. It in unlikely that this can be used for slumping or casting, but it is a great aid for the cast making process.
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| RTV T30 Silicon rubber |
RTV T30 Silicon Rubber is the ideal substance for almost any kind of casting and moulding purposes. It is of a medium weight and viscosity (depends on the type of silicon, the higher the number, the more durable and strong is the outcome) . This particular type is used with a solvent, and can be used with thousands of different materials, since it is non-sticky and has a wonderfully high level of detail impression.
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| pouring the silicon into M80 block machined with the router |
The hardening time may vary, it can take from 6 hour up to several days, or in some cases, when the liquid has not been mixed well enough, it may produce what I call a “half boiled” egg effect.
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| silicon cast out of the mould |
It is an extremely flexible and durable material, and is resistant to high temperatures. The silicon positive mould was used for vacuum forming and it retained its qualities after the procedure. The mould making process is fairly straightforward and the only inhibitory factor is perhaps the cost; it is too expensive to be simply used as a waste mould.
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| Standard filler |
Tetrion filler is simply one of the standard fillers used in construction. It is relatively heavy and does trap air bubbles after drying. The filler is easy to apply due to its hard cream like quality, and the air drying time is about 6 hours, depending on the depth and the positioning of the material. It proved to be durable to high temperatures. The surface of the dry filler piece is easily cracked and damaged where there is a weak point. It is odourless and has an off white colour. It does not have a sufficient level of details, so perhaps this could be a huge disadvantage for intricate models.
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| Plaster |
Lafarge plaster (prestia classic)is one of the best known materials in casting and mould making world, perhaps due to its “value for money” factor. It is of moderate weight and density and not very difficult to prepare. The tricky part, however, is to determine the right setting time to work with, as later this will characterise the success of the end piece. The impressions captured by plaster are of high quality, however even after full drying, the piece remains rather fragile. In order to use this for glass moulds, it will be necessary to mix it with silica.
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| Fire cement |
Sika fire cement is indeed a very heavy weight alternative and perhaps the air drying is not a sufficient option, a firing is needed, which makes this substance time consuming to a certain extent. It is relatively soft and simple to shape, it is odourless and takes high temperatures very well. It has a warm grey colour and a very smooth, glossy finish can be achieved. When making a big scale model, the weight can become a worrying issue.
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| Liquid colour resin |
Pebeo colour resin is a precious material to work with and the outcome is a beautiful surface that is amazingly light weight. The packaging warns that this is an extremely dangerous product for the environment, which instantly makes one think twice before committing to a bigger project, even though it has no smell or other external indication of harmfulness. When poured, it traps millions of air bubbles, which make the structure weak perhaps plenty of air holes are needed. It responses to high temperatures and softens, might even melt, which suggest a possibility of reusing it. I was considering this as an equivalent to glass, but it is the wrong material perhaps for many reasons, like the cost and the artificial chemical consistency, the fact that it is not as translucent or reflective as glass.
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| 3mm transparent acrylic |
There is a wide variety of these products available, in all kinds of thicknesses and sizes, and this along with the relatively reasonable price, make perspex so popular. It is lightweight, compared to glass and has a much lower melting point than glass, in fact it can be manipulated by a heat gun (about 700 degree Celsius) . However, when heated, it produces unpleasant fumes and after cooling, a small number of air bubbles appear on the surface, perhaps a gradual annealing might solve this. It has a high gloss even surface and is an attractive alternative to glass. This could potentially be used for slumping.
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| Polyester resin |
Clear casting polyester resin is a relatively straightforward material to deal with, comes as a liquid with a hardener. The extremely prohibitive factor is the smell, which is very strong and toxic, if working in badly ventilated area.
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| Polyester resin drying in a chamber |
It is quite a heavy and dense product. It is prone to trapping air bubbles and needs to be poured into a cavity with utmost care and attention.It is not suitable for use with foam materials, as it eats through the foam, which perhaps could be preventing by securely varnishing the surface before pouring the resin.
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| The dried polyester resin |
When drying is complete, the resin looks really beautiful and has nice tactile feel to it, with beautiful reflections and translucency clear and magnificent like that of a glass. Unfortunately the dangerous smell of this resin makes it almost impossible for fabricating a big sculptural piece.
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| glass wax |
Glass wax looks like a mineral and does not react to body heat like the natural wax. However it responds well to a heat gun and melts easily producing paraffin like smell.
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| melting glass wax with heat gun |
On the other hand, when a blow torch is applied, it simply burns, while still melting.
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| Handheld torch applied to a glass wax |
It its original form, it is has a frosted looking surface with sharp edges,but after melting it becomes clear and glossy and indeed does look like a glass. Despite this, it is still more of a wax than a glass, therefore it breaks easily and has very low durability in general.
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| Addition cure 13 |
Addition Cure 13 is very similar to Silicon and comes in two parts A and B , which are mixed in equal volumes. It creates translucent human skin colour like soft but durable piece and has a high level of detail.
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| Addition cure mould for silicon casting |
It works really well with silicon as I was anticipating and is incredibly easy and pleasant to use. But, again, the cost is the major prohibitive factor for architectural applications.
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| Polyurethane blocks |
Sike produces a wide range of polyurethane blocks, which are the "Holy Grail" for CNC fabrication on 3 2, 3 and 5 axis milling machines and routers. Generally the series start with more lightweight materials like M80, then with higher the number, the surface gets harder and the piece gets more dense harder, for example M1260 is four times the weight and the density of the M80 and is extremely resilient.
The surface f M80 is fragile and easily damaged; it constantly covered in its own dust. The M80 works really well with the 3D router and makes a higher quality finish than polystyrene. Due to its soft structure, it is easily cut with other handheld tools.
This exercise was targeted to test as many materials as possible and also to investigate into the relationships of different substances. Each material with its characteristics allows certain operation while in the same time hinders others. It is also interesting to compare those results with the digital materials generated with the help of the computer, of course the latter happens only with a click of a mouse.
Next I will be experimenting with glass and "refractory" moulds, which are the so called waste moulds for warm glass (p120 Helga Watkins-Baker, "Kiln Forming Glass", 2010).
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