Document dating and, therefore, the time that a document and/ or ink could have been once placed on the paper, is one of the most difficult and hardest problems to solve in forensic science. This is mainly due to the great variety of inks that exist on the market, the complexity of chemical processes that inks undergo from the time they are entered on the paper when they begin their aging process and the amount of external factors that can influence this aging process (environmental factors: light, humidity, temperature; in short, storage conditions of the document) . In spite of the complexity of the issue, important advances have been made with the single objective of determining for how long the ink has been deposited on the paper, which would lead to establishing the date on which the document was produced. The modern writing instruments, are those we can find nowadays in any store of any country and, therefore, those that are most frequently used in questioned documents – are divided into two fundamental groups : 1. Ball point pens: Containing oil-based inks and whose colorants are dyes. 2. Non ball point pens: Containing water-based inks and whose colorants are dyes as well as pigments (one, the other or both). In this second group fountain pens, roller ball pens, as well as markers and gel ink instruments are included.