Inks do not maintain their original properties forever. Many conditions can affect the aging/weathering of the various types of inks used today. Ink formulation, paper surface, temperature, temperature fluctuations, light exposure, storage and humidity can gradually and drastically over time affect the optical properties of the original ink. Changes to ink can vary from a lightened image, a change in color to the entry becoming virtually invisible. Common examples are the signatures on old elevator inspection certificates or other aged official certificates or diplomas that contain numerous signatures produced with different pens. Below is an example of a metal water inspection plate where the original ink entries have over time faded and had become indecipherable. However, with the use of the Foster + Freeman VSC-4® the original entries were recoverable.