A large collection of ink samples fills storage space at a small laboratory in Washington, D.C. The samples are kept inside a mix of soft, plastic bottles and small glass containers. To the untrained eye, they are just a lot of dark liquids with strange names like “moldy sponge” or “green grass.” But to the United States Secret Service agents who use the ink samples, they could provide information that saves the life of the president. Agents say the samples also could help them stop criminals from reproducing money illegally. The ink library at the laboratory has more than 15,000 samples. They come from writing instruments and printing machines dating back more than 85 years. The collection is the result of one man, Antonio Cantu. He started collecting samples in the 1960s. Cantu was a well-known investigator and former chief chemist at the Secret Service.