Vintage 15ct. Gold Opal ChipTube Brooch

I'm fairly certain it's 15 ct gold based on the marking in the last photo. There is no damage to the pin and it is still in working condition. One of the markings kind of looks like what you would see for a 1696 London Hallmark, but I'm being more conservative dating it to the late 1800's. I'm not sure if it at one time held liquid, if it did there are no marks on the inside of the glass indicating that was the case. This is one of my favorite pieces of Grandma's so it is sentimental.