Thanks for the info. I don't think I'm going to invest in a humidity chamber. What happens when you iron a note?
It's like cleaning a coin. There are telltale signs the grading companies pick up and will note on the holder. Just like a 'Details' label on a coin.
If you do, never spray with just regular H2O. Use distilled H2O, but with a very fine mist about two feet or less above it. Afterward, after a flip over you must place the currency between two clean sheets of archive paper. You place the currency in such paper with a very fine mist of distilled water from above and not directly and place it in a large book, then place a heavy weight on top of the book as a press for a period of time till dried. Think about how conservators that you send notes to, make them look better, and how they do it. Good luck. Do what you want, if the note is worth doing this to you.