One of the most basic things you should familiarise yourself with when expanding your education on opal are those partially man made stones known as doublets and triplets. In summary, these stones are slices of opal glued to a black backing, designed to imitate the appearance of a solid black opal. Adhering the slice of opal to a black backing causes the colour to become much darker and more vibrant. However doublets and triplets are generally much cheaper than solid black opals as they only contain a small amount of genuine opal.