In the days of Isabella and Stewart (the middle 1850’s) it was considered the height of vulgarity to own or wear colored stones. So, rubies, emeralds, sapphires, topazes, or any other stone of that sort were avoided, and diamonds and pearls were the only really acceptable gems to be seen with. White opals were just barely allowed, but only as long as they didn’t show too much color.
In the old photographs you will never see a woman decked out in the mid 1800s with anything other than white or colorless gems. This fashion continued until the turn of the century and even a bit beyond.
This brings me to the point of Stewart’s gift to Isabella, that massive colorful explosion of passion bought from an enthusiastic Maltese jeweler. To receive as one’s engagement ring a mammoth pink diamond was just awful! Stewart is a man of science who neither knows nor particularly cares what the fashion of the time is for engagement rings. If his brother, Timothy, had been around to advise him on his fateful trip to the Maltese jeweler, all would have been right BUT Isabella was truly aghast at this eternal present and used all of her well learned poise not to cry out when she received it. She really would have been far happier with a smaller white diamond set in a platinum modest setting.
Ladies had modest engagement and wedding rings (matching metals and stones, thank you) and then wore their eye popping gems during evenings, balls, nights out and grand soirees. That was when the “little” wedding and engagement rings were left at home.
Engagement rings were set with a stone of about 1/2 carat or less in the center, round cut. They were surrounded by much smaller stones also round cut (any other cut was also considered vulgar). All in all we would consider it all very dull and far too understated while being fussy. A great many of those engagement rings have been taken to the modern jeweler and transformed into something more modern or become bit players in larger settings. Here is a page of good examples of the kind of rings I mean.