The present invention provides an emerging security or authentication feature for identification documents and other objects. The security feature is constructed using two differently emission-decaying inks. The inks are arranged so as to convey a first pattern when they are both exited. A second pattern emerges as a first and more rapidly decaying ink decays, but while a second and relatively longer decaying ink still provides emissions. The second pattern can be alphanumeric characters, a barcode, a pattern that will yield a predictable frequency domain representation, a digital watermark, etc. In one implementation, the first pattern is a first machine-readable code and the second pattern is a second, different machine-readable code.