while he would confirm it was being used on red coral, he would not tell me what the acid was. He did indicate that they just 'painted' it on and then neutralized it (I guess with soda).
Coral chemically is very similar to the Mexican ‘onyx’, that is
mainly calcite. I would think that what ever is used on onyx can be
used, though it may need to be more dilute, on coral.
My observations. From Slowly warming, I think spring actually may
have found us, Calgary, Alberta, Canada.
Karen Seidel-Bahr the ‘ROCKLADY’ @Rocklady K.I.S.
Creations May your gems always “Sparkle”