In the early days where arranged marriages and “marriages by purchase” were commonplace, the engagement or betrothal ring had two purposes. It served as partial payment for the bride as well as a symbol of the groom’s intentions.
The first diamond engagement ring was said to have started in Austria in 1477, when Archduke Maximilian gave one to his beloved, Mary of Burgundy.
However, the use of other gemstones was popular in the 18th and 19th centuries. It was said that the first letters of the stones used would often spell out the name of the giver or a word, such as “dearest,” for diamond, emerald, amethyst, ruby, epidote, sapphire, turquoise.
Then there was also the “gimmal ring.” This was a three-part ring with two clasped hands on it. During the engagement, one part was worn by the bride-to-be, one by the groom-to-be, and the third by a witness. The three parts are reunited on the wedding as the bride’s wedding ring.
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Sources:
Engagement Ring Customs Through History.
http://www.diamonddiamonds.com/diamond_engagement_rings/Engagement_Ring_Traditions.html