The Rosette has only been the UK SHEFFIELD Town mark ca. 1975 - Present
The old European cut diamond was a development of the "old mine cut" diamond. After the bruting machine was invented in 1891, the girdle of the old European cut diamond was rounded. It was the forerunner to the modern brilliant cut.
It appears you have a late 19th century early 20th century old European cut diamond set in a ca. 1975 plus white gold ring.
White gold was introduced around 1915. It was the prefect imitation of the more expensive platinum which was popular in the early 1900s.
