We recommend the Pantone Graphics guides are replaced every 12-18 months, which is stated in the front of the guide as well on the back cover of the guides. The ink pigments will fade with time, handling and exposure to UV light (and environment) and as the paper ages the optical brighteners used to make the paper white will fade and the paper will yellow with oxidation. This will cause a shift in the colors appearance and the accuracy of the visual color to change from its original intent.