Acetate (C 2H 3O− 2)
Acetate frames are lightweight and often considered better and higher quality than plastic frames. They are known for their hypoallergenic qualities and are therefore a popular choice amongst those with sensitive skin. Unlike certain plastic frames or some metal frames, they are less likely to cause irritation.
Titanium (TI)
From the Latin titans, the first sons of the Earth, Greek mythology.
Discovered by Gregor in 1791; named by Klaproth in 1795. Impure titanium was prepared by Nilson and Pettersson in 1887; however, the pure metal (99.9%) was not made until 1910 when Hunter heated TiCl4 with sodium in a steel bomb.
Sources
Titanium is present in meteorites and the sun. Rocks obtained during the Apollo 17 lunar mission showed presence of 12.1% TiO2; rocks obtained during earlier Apollo missions show lower percentages.
Titanium oxide bands are prominent in the spectra of M-type stars. The element is the ninth most abundant in the crust of the earth. Titanium is almost always present in igneous rocks and in the sediments derived from them.