| This article is an orphan, as no articles link to it.
Please add a link to it on another article. Suggestions may be available here.
Banknotes are considerably more fragile than their coin counterparts, as a result of being composed of thinner, more brittle materials such as paper or polymer. It is common for some paper money to become dirty, soiled, or torn during circulation. Dye packs are used by some banks to mark notes stolen by robbers with colored dye, thus rendering the stolen currency useless.
Coins, even though they are often considered less vulnerable than banknotes, are still susceptible to damage. They can be worn or scratched through circulation, and some collectors accidentally or unknowingly damage their coins by polishing them, cleaning them, or exposing them to air and other harmful substances, such as sulfur and PVC. Some metals, such as copper and iron, are more reactant to air than others, and may become green or red as time progresses if and they are not stored properly. To combat this, a number of suppliers, such as the Littleton Coin Company and Krause Publications, offer varieties of protectant holders that protect coins from the environment.