Help please I may have burnt silver

I’ve invested in a sterling silver charms and I tried to wash it with baking soda vinegar salt tin foil and boiling water.
when I did so one part of it appeared burnt. but only one area did and I noticed that this particular charm opened and only one part of it had a silver hallmark. and that side didn’t burn, only the other bit. can sterling silver be burn in boiling water? or is that section not real silver? if it is does anyone know how to remove burn marks?? thanks so much

I would never use salt when cleaning silver, it is extremely corrosive for silver, and can do damage in very little time. Jeffrey Hermann has a very comprehensive site on caring for silver here, and he’s a genuine expert: Silver polishing, silver cleaning, and silver storage. Check through there and see if one of his methods can’t help improve things for you.

What may possibly have happened here is that the “burnt” section was electroplated and the over-aggressive cleaning has removed all of the plating exposing the base metal to the corrosive action of the hot solution - just a guess though.