Maybe it didn't start out as a simple pin,the stone has been removed/replaced then poorly remounted.There is 4 solder points on the back where...
Horn bird cane handle. https://www.invaluable.com/auction-lot/a-horn-handled-wood-walking-stick-with-a-sectiona-127-c-c264a72819
It has koftgari/zogan style overlay of silver wire.The designs were chased and not engraved.
#4 looks like a Dentalium/tusk shell,the backside surface seems strange,metal pealing off?
black lip mop
If it is an actual hole,it's put there so the piece doesn't blow up in the face of the goldsmith when the solder seam is heated.
A vise and a pair of pliers.
There is a "Wrinkle stone" which comes from China.
Silver plating is very thin and would not be noticeable on the turned metal. Plating thickness.... 0.0005 inch (0.013mm)
Engine turning machine cuts/removes the metal like a lathe,the machine video I posted imprints/embosses the patterns onto the metal.
It was probably made on a rolling machine. [MEDIA]
Natural black opal has a black base with color flashes,matrix opal can look like sandstone with color flashes. https://www.gia.edu/doc/SU91A3.pdf...
Yes an opal soaked in a sugar solution and dropped into sulfuric acid to turn the sugar black.
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