Can a size 10 ring be resized to a size 5 1/2. It is a marquise shape centerstone with three small round stones on each side. What is the average size to size capability.
It really depends on how well made the mounting is. If it is a casting, then it could very easily create some serious problems. I am assuming this is a woman's ring and was probably sized up to a ten at some point in time. A talented goldsmith can usually tackle a job like that. It just requires a bit more work and reinforcement in some cases. The side stones could possibly loosen up and even fall out from bringing the ring in but these could be reset and the mounting reworked if necessary.
Cindy
Cindy is completely correct in this. That job is not for a newbe with a blowtorch. Make sure the person doing the job is very experienced.
You might consider having a new ring made for your diamonds.
Good Luck.