Disappearing inks are used in textile industry such as dressmaking crafts and as a kind of teaching material; for example, printed questions are visible and the spaces for an answer exhibit invisible disappearing ink. The answers only become visible using a coloring assistant. This research was conducted on the preparation of disappearing inks using different concentrations of thymolphthalein (Th-ph) and O-Cresolphthalein (O-Cph). The prepared inks were applied to different types of handwriting papers. It was found that the handwriting stability increased by increasing thymolphthalein (Th-ph) and O-Cresolphthalein (O-Cph), or alkali concentration. Deciphering of the faded documents was evaluated by different methods. Commercial paper C2 surfaces gave the more handwriting stability than other paper, the order of stability were C2 ≥ C1 > Azhar >Xerox > C3 >C4 > Edfo. All the faded documents were visible when treated with alkaline solution. When the faded documents surfaces are exposed to the thermal effect there is no change in all the faded documents.
Disappearing inks have been used in different fields, but it may be abused in forgery and counterfeiting.