Antique French Sterling Silver Penannular Kilt Cloak Pin Brooch Rose Cut Paste

I have for sale an interesting french silver penannular kilt cloak pin/brooch. French hallmark of a crab stamped in the metal - for 800 silver. X-Ray analyized and the piece is actually sterling silver. Not uncommon to mis-stamp pieces to pay a lower tax. At one point this was gold washed and small amount of the plating remains at the top center. Anyway, the mark has been used since the late 1790's up until around the 1970's (going from memory) so I don't see anything other than the stones that might date it. At one point, this appears it may have been gold washed. The paste stones in this are old rose cut with mounting consistent with the 1800's time period. The stones are all glass. Faux sapphires, faux garnets, faux emeralds, and a faux ruby with some facet wear. God bless the french. I am not sure what the blue bit in the pin is. (I have no idea what the material is). There is a small damage area in the piece. I do not know if it was a casting issue that was repaired and showed