Featured Cleaning and dating turquoise stick pin

This little beauty can’t be quite restored to its formed glory but it desperately needs cleaning. Before I attack it with jewellery foam, does anyone know what the black stuff is that the turquoise is set into and will it resist being cleaned?
After having managed to dissolve a previous necklace that had gelatin based sequin discs (who knew?) I’m leary of cleaning without researching first!.
It may be gold, it tests as such on a stone but until it’s clean I can’t really see what’s going on with it!
Also, any ideas for a date would be fab.
Thanks for any thoughts

 

Nice! The turquoises are set in metal (Oxidized silver?) in what appears to my eyes to be a panel, further set in the pin mount (original to the piece, or a marriage? There is a gap around it).
The pin unscrew, see the threaded end
1860s is my feeling for the date.
You can safely use your silver foam, just not hot water if the panel is glued in the mount.

 

That’s brilliantly helpful Kyra, Thankyou. It didn’t occur to me that it was set in silver that had oxidised. I think it is all original, unfortunately it has been squashed at some point in its life which has shifted the turquoise panel hence the gap.
I will get cleaning

 

Persian turquoise that.

 

Fab, Thankyou