Rose Cut Diamond Pin - When was 14k gold first used in jewelry.

I'm looking at what is clearly an antique diamond brooch, foil backed rose cut diamonds, hand cut diamonds, stone sizes all over the map, set in yellow gold which tests out to be 14k.

This is a very large brooch and the floral style appears distinctly Georgian, but it's the karatage of the gold that gives me pause. The piece is not stamped. A history of work to the piece, some good quality, some not so good, using lead solder, is evident on the closed reverse of the brooch. It was purchased perhaps fifty to sixty years ago from a high end jeweler in the middle east and was said to have had a Russian provenance.

As I recall however, Russian diamonds were known for being higher quality, and very white, and these diamonds are K-M or higher in color. A very pretty piece to be sure, but even after going through a dozen or more books on antique jewelry (to no avail) I'm still struggling to accurately identify the age. The 14k gold karatage in use here may help. Any thoughts as to age on your end?