There are three types of dye used in CD-R discs. The most common is phthalocyanine, and it is usually light green. CMC Pro (formerly Taiyo Yuden) uses cyanine dye. It is usually teal or dark green. Verbatim uses phthalocyanine dye on some discs, and AZO dye on others. AZO dye is usually dark blue or blue-ish silver. The metal layer on the disc is usually made of silver. Archival discs and some professional audio discs use a gold top layer. Verbatim UltraLife discs have a silver main layer, and a gold upper protective layer, providing the reflectivity of silver and the chemical stability of gold. Early cyanine discs could decay and become unplayable within a few years. Recent cyanine discs have preservatives added to the dye to prevent this from happening. AZO and phthalocyanine dyes do not need preservatives and do not decay easily.