Sizing a rhodium plated ring

When sizing a rhodium plated ring, is there any trick to see a seam
from a previous sizing?

Some one told me that the ring can be dipped in alcohol and boric
acid, lit and burned off, and a line will be visible where it had
been sized before. I know you can heat up a shank and previous solder
seams will appear, but not when it is rhodium plated. Anyone heard
this or tried it? Also, if you heat a cast and sparexed piece of
silver, and turn it black or brown, and then apply flux, is it true
that heating it oxidizes it and you are defeating what you are trying
to accomplish. Always flux prior to soldering so it does not
oxidize, which will add unwanted problems, correct?

Richard in Denver

Hi, I have never tried this but I have been told that iodine will
make a previous solder line appear…Just polish the shank so the
rhodium is gone and apply the iodine. Good Luck, Mark