Blue or black ink is most typically used for signing papers. While both are acceptable, many people believe that "blue" is the better option. The use of blue ink also suggests that the document is an original rather than a replica. It is not illegal to use other colors besides blue for writing documents that will be filed in the court system, but using other colors may not give the impression of importance that judges and lawyers expect from all parties involved. Black ink was originally made from soot taken from burnt wood. Today, it is produced by mixing carbon black with oil or wax and adding acids to adjust the pH value. Although black ink is commonly assumed to be non-reactive, it can stain fabrics if it comes into contact with them. This means that professionals who work with papers such as librarians and archivists should avoid wearing clothing that they do not want stained with black ink. The best way to ensure that documents you sign are official is to use only blue ink. However, if you work in a fast-paced environment where you need to sign lots of documents without having time to find the right color, using black ink is acceptable too. All things considered, blue is the safest choice.