Tattoos used for cosmetic rather than artistic purposes are a special class. The ink colors tend to be pink, white, light brown or rust-colored. The pigments used to make the inks may or may not contain iron ores. Through an unknown chemical reaction, iron-containing inks may darken irreversibly to black or dark gray when treated with a q-switched laser normally used for laser tattoo removal, such as a YAG or Ruby laser. Attempts to further remove the tattoo may succeed after multiple treatments or may fail altogether, requiring surgical excision. The mechanism is thought to be the reduction of the ferric oxide (Fe2O3, “rust") to ferrous oxide (FeO, black) but it is unknown exactly why it occurs with q-switched laser exposure.
There is a great degree of variability in inks used for cosmetic tattooing. Some artists also do tattooing and cosmetic tattooists may use artistic ink or ink that does not contain any ferric oxide. In that case, the tattoo should respond to laser treatment similarly to another artistic tattoo anywhere on the body. For this reason, when approaching the treatment of cosmetic tattoos, especially on the face, extreme caution is used. Patients getting tattoo removal should be warned about the risk of irreversible conversion of their cosmetic tattoo from flesh or rust-colored to black. With that in mind, a test spot is then performed in the least exposed part of the tattoo (about 3 millimeters wide). The patient is then brought back in 1-2 weeks for a re-examination. If there is no darkening and/or if the patient wants to continue treatment for the rest of the tattoo then treatment may proceed. In some cases in the medical literature, even a tattoo that turned black may still be removable with lasers but it may require many more treatments than originally anticipated. Some patients have elected to have such a tattoo surgically excised.
The bottom line is that, if possible, it would be good for clients of cosmetic and artistic tattooists to know what kind of ink they are receiving. The ideal ink is one that is most easily removable without any complications if the wearer changes their mind about it.