Cracking/crazing info.......... https://www.opalauctions.com/learn/did-you-know/what-is-the-difference-with-crazing-to-crack-in-an-opal
At the time the piece was made,it would have been illegal to add a gold mark to it.The opal is very crazed probably do to being exposed to too...
Looks like it was fused together using a colloidal or eutectic soldering process. The whole piece was polished and the areas not having applied...
Looks like the ring was poorly made by a beginner hobbyist/student.
All of these links are for for rose cut stones,the OP's diamonds are uncut rough diamonds.
Polki diamonds usually from India.
If the bezel is Nickle silver or another base metal it is harder.
Many makers today prefer the .999 fine over sterling bezel wire as it is easier to bend the edge over the stone.
Sawtooth bezel has been commercially available for over 60 years....
Jasper
@Any Jewelry is the expert.
See if a magnet is attracted to the black side. Backside can be cleaned a bit with a sunshine,front side with a mild soap and soft rag and it must...
The molds can be made with a variety of materials like bronze,soap stone ,wood,silicon putty,etc. A number of historical reenactment groups may...
It doesn't appear anything was cut out,it was cast and the 2 parts of the mold were not tight where the filled area is....
Too much bright light and reflection to see any detail about the stone setting. They appear to have standard bead setting.
Blue sapphires have a variety of colors/shades depending on the location mined,heat treatment,faceting of the stone....
Casting investment is poured over the wax pattern in a metal flask. If the water/investment ratio is off when mixing the investment it causes air...
Looks like there are casting bubbles on both sides of the leaf.
People have used steel blocks to hold the metal for some time,one example......
Excess solder and no clean up on the bezels,probably not made by a professional.
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