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 anniversary widely marked as her Diamond Jubilee. The origins of the current gift conventions date to 1937. Before that, only the 1st, 5th, 10th, 15th, 20th, 25th, 50th, and 75th anniversaries had an associated gift. In 1937, the American National Retail Jeweler Association (now known as Jewelers of America as a result of an organizational merger) introduced an expanded list of gifts. The revamped list gave a gift for each year up to the 25th, and then for every fifth anniversary after that. Lists of wedding anniversary gifts vary by country. The traditional and modern U.S. versions were compiled by librarians