Sterling silver leaving a mark on skin

[Littlewhitefeathers]

Hi, I have been making sterling silver cuff bracelets. I have had them tested and hallmarked so they are definitely sterling silver.

Once I stamp quotes on them I use platinol oxidising solution to define the letters then polish off the excess with a polishing pad.

I polish the bracelets by using sanding pads of various grits then polishing with a polishing pad.

One of my customers recieved their bracelet yesterday and wore it over night. It has letters on the inside.

This morning she says it has marked her wrist but I am confused as to why? Any ideas?

See pic attached. Thanks