If you are a map or natural history aquatint collector, the ideal condition is when the sheet of paper has the natural waviness that speaks to the natural qualities of the celluouse fiber.
This is especially true of the Whatman paper of the 18th and 19th centuries. PLEASE dont allow some clown who calls himself a "paper restorer" to charge you $1000 to flatten something that should have a natural waviness or rippling to the sheets.
A map should NEVER be flat. If it is flat, that means that a reducing agent has been used in restoration by someone who is incompetent. They have weakened the cellulose fiber to make it flat. This ruins the molecular structure.
And sometimes staining in the 16th century map is desirable if it depicts the aging of the wheat paste used to hold the sheet together or to hold it on to the tab that was part of the book.
You are welcome to come to Arader Galleries in all of our locations to learn what good condition really is.
If you dont pay attention now someday when you know better you will be sickened to learn that something with bright white paper that is flat is actually in the worst possible condition. A collection filled with these horrible wrecks will depress you when you learn that objects are great when they are as they were when they were published plus normal aging, oxidation of the copper in the green and oxidation of the iron in the ink.
I will give you a FREE consultation anytime. PLEASE be careful. You may have something that truly is great that will be ruined by an ignorant or dishonest paper restorer. Most of them have no idea what they are doing.