I'll try to answer your questions about the antique platinum ring.
But first, is the ring set with stones? If it is set with stones
the correct way was to unset all of the stones and then either weld
or high temp platinum solder as needed. However we are now blessed
with laser welding which will handle this job perfectly without the
risk and cost of unsetting. Many fine old rings have been
contaminated with gold solder because the repairman took the easy
If the ring was originally made by knowledgeable craftsman it was
most likely welded, not soldered together. He would fusion weld the
two half's together so you will not be able to find solder seams. If
the ring has been rhodium plated then you must first strip the
plating off to find any platinum or gold solder seams. Again, with
laser welding chances are you won't have bother with stripping. Do
yourself and your customer a favor and use a laser.