In the case of the VX-4C the choice of copper, with its excellent electrical characteristics, would seem a logical one, but it brings with it significant problems. In its purest form it is relatively soft, a property at odds with the need for precision machining, and its surface readily oxidises upon exposure to the air, forming an unsightly layer which is considerably less electrically efficient. Whilst maintaining the high conductivity of the pure material, the addition of tiny amounts of the rare element Tellurium to the copper vastly improves its machining characteristics, making the necessary geometries possible.