Hi there and thanks for the photos and writing in with the following general antique jewelry question:
"I found these while going through some of my late great-aunts things. I would love to know about when they were made so perhaps I can determine who they would have belonged to. She supposedly lost her wedding ring years ago which was the only diamond she had, so I am doubtful that they are hers. But anything is possible!"
Maybe great-aunt's diamond ring wasn't really lost at all :-) OK. The metal Platinum is a big clue. Platinum, a heavy, strong metal was not used in jewelry making until the late 1800's. It continued to grow in popularity and reached a peak in the early 1900's - 1930's. When 18k white gold was introduced in 1915, it being cheaper metal, the variables started to change.
Looking at the diamond, it appears to be a brilliant cut, invented in the early 18th century. Many people mistakenly think the brilliant cut was invented in the 20th century but it goes back further. A fashionable young women in the early to mid 1900s, would lean towards a platinum diamond engagement ring.