A lens works by refracting (bending) light as it passes through the material. For a material to be used to make a lens, it must be transparent or at least translucent to the type of light intended to be used (e.g., visible light for optical lenses). Glass, Sapphire, and Water are all transparent or translucent materials that can refract light, making them suitable for manufacturing lenses. Aluminium is a metal that is opaque to visible light. Light does not pass through it but is reflected or absorbed. Therefore, Aluminium cannot be used to make a convex lens for visible light.