Most banknotes you will handle will be made of some sort of paper. Although a number of countries nowadays are adopting a polymer substrate (type of plastic), the vast majority of banknotes available to the collector will be made of paper in one form or another.

Clean hands are essential to prevent undue oils and dirt transferring to the paper.
Ensure that there are no fans or breezes nearby which may blow the banknote from your hands. There should be no food or beverage in the nearby vicinity. There have been many cases of someone removing a banknote from a holder and then a third party ends up accidentally spilling something which stains the banknote. This is of particular concern at busy show bourses where the normal hustle and bustle of patrons may create this scenario. Removing the banknote from its holder or sleeve should be done with care. Once out of the holders, simply treat the banknote with care however not so gingerly so as to drop it. Lightly feeling the surface of the note can tell you a number of things.

Once you are finished handling the banknote, place it back into its holder. This should be done with the utmost care as this is when most banknotes become torn or creased. If you are viewing a dealer's banknote and are having any type of trouble getting it back into the holder, it is always better to hand the banknote and the holder back to the dealer and allow them to complete the task.

By virtue of its nature, a piece of paper money has a limited life expectancy, which is directly proportional to the amount of handling it receives.

From Printer to Bank to Wallet or Your Collection

The handling of a banknote used to begin at the printers with a manual counting of the sheets both prior to printing and then again prior to cutting. This is now done mechanically with little to no evidence of handling.

In the very early years of banknotes, the actual cutting was done by hand which is noticeable by varying margin sizes of many countries banknotes.

After cutting, the banknotes were recounted, stacked and bundled. Bundling was accomplished by a variety of different methods and often created marks on the edges of the banknotes in the bundles (or bricks) as well as the banknotes on the top and bottom of the stacks.

The bundles are then stacked and either stored or shipped to the appropriate issuing authority. Storage was not always done in climate-controlled environments and in certain countries the effects of the natural environment are noticeable on the banknotes. This is particularly noticeable in banknotes from countries with a tropical climate. While in storage vaults, banknotes were often counted regularly for auditing purposes. They were normally kept in their respective bundles and often only random bundles were counted, however in the case of certain issuing authorities all bundles were regularly counted which created "counting creases" on these banknotes. If a banknote made it this far without traces of handling, these counting creases were often the first visible signs of handling manifested.

Upon requisition by a bank or bank teller, the banknotes would be further counted, usually more than once, before being released to the general public. Certain countries issued banknotes that were quite large which necessitated folding by the tellers in order to fit them into their boxes or drawers. Even if a teller did not need to fold the notes, it was certainly a necessity for a customer to fold the banknote to fit it into their wallet or purse. Banknotes from these countries are extremely difficult to find without varying degrees of folds in even the cleanest, crispest banknotes put away during that time.

Modern equipment and machinery has created a process whereby a banknote may now remain virtually untouched and pristine until the moment a bank teller hands the banknote to a customer.

The above steps relay the difficulties that collectors of old notes / times had in
obtaining truly UNC notes. Many other factors, unrelated to grade, created
additional obstacles for the early paper money enthusiast including economic
factors, the relative unpopularity of collecting paper money in those days, the
stigma attached to paper money in relation to precious metals with intrinsic value,
not to mention the fact that paper money was almost always worth more than
coins and very few individuals could actually afford to "save" a piece of paper money.