In natural form, Opal is made up of closely packed spheres of silica as silica oxide, and water in varying amounts up to 15%. Water fills the gaps between the spheres of silica oxide causing diffraction of light at specific points and creating the "fire" effect. Lab created opals are grown in a laboratory using pure silica or a polymer-resin, instead of water, to fill the gaps between the silica oxide spheres. The process takes from 1 to 2 years and results in a similar structural and chemical makeup to natural opals but with increased stability and durability. The process of growing opals in a lab was first invented by Pierre Gilson Sr. of France in 1974.