Polyurethane (Crystal Clear)

Most famously, this clear transparent resin was used by Rachel Whiteread to create Untitled Plinth, her inverted 'mirror-image' cast of the Fourth Plinth in Trafalgar Square. 10 tonnes of this material were poured in one continuous casting process to create the largest resin object in the world. The polymer has an unusual watery transparency, hence the name 'Crystal Clear®'. For this reason, it has been used in prop-making to simulate ice cubes and eyeballs. The mechanical properties of polyurethane resins are not really affected by UV light, but they can discolour over time when exposed to sunlight. This material contains chemical stabilizers that make it UV-resistant and non-brittle, making it very suitable for open-air artefacts. Regardless of the end-product or even type of polyurethane you are using, the way in which you use polyurethane resins is always the same: the raw materials come in two parts, a liquid isocyanate (a very reactive chemical derived from petroleum) and a polyol (a long-chain alcohol), which are mixed to a specified ratio to create a reacting liquid, which is then poured into a mould or onto a surface and left until it cures to form a solid object. This relatively low-tech process makes it a useful material for tinkering and making prototypes.