The 40th wedding anniversary is known as the ruby anniversary to symbolize how love and passion are still strong after being together for 40 years. As such, the traditional anniversary gift either contains an actual ruby or something ruby red in color.
Giving specific gifts for different milestone anniversaries started during the Middle Ages in the Germanic region of Europe. Only the 25th and 50th years were marked by gifts in silver and gold, respectively. In the Victorian era, the 75th anniversary was added as the diamond anniversary. It wasn't until 1937 that the American National Retail Jeweler Association issued a list matching a material with each of the first 20 years and then each fifth after that, up to the 75th.