Tin pest related problems such as tin whiskers. At 13.2 °C (about 56 °F) and below, pure tin transforms from the silvery, ductile metallic allotrope of β-form "white tin" to the brittle, nonmetallic, α-form "grey tin" with a diamond cubic structure. The transformation is slow to initiate due to a high activation energy but the presence of germanium (or crystal structures of similar form and size) or very low temperatures of roughly −30 °C aids the initiation. There is also a large volume increase of about 27% associated with the phase change to the nonmetallic low temperature allotrope. This frequently makes tin
Wedding ring phrase of significance to the spouses. In many nations the engagement rings are plain while the bride's wedding ring commonly is bejeweled. Some customs include the wedding ring as the final of a series of gifts, which also may include the engagement ring, traditionally given as a betrothal present. This custom was practiced in ancient Rome and is possibly much older. In several traditions, the best man or maid of honour has the duty of keeping track of a couple's wedding rings and to produce them at the symbolic moment of the giving and receiving of the rings during the