An optically readable media (10) has an information-encoding layer (16)
and at least one color-forming layer (12) that embodies an optical
readout-limiting mechanism. In a first embodiment the at least one
color-forming layer contains an additive that does not interfere with the
optical readability of the media for a duration of a readout period. The
additive, upon exposure to a source of optical radiation that is suitable
for reversing the color-forming layer from an optical readout inhibiting
state to an optical readout enabling state, undergoes a transformation
that maintains the color-forming layer in the optical readout inhibiting
state. More specifically, exposure to the source causes the color-forming
layer to photobleach and the additive to oxidize, where the oxidation of
the additive permanently inhibits the optical readability of the media.
The additive may be a leuco dye. In one embodiment the color-forming
layer is comprised of
3-[2,2-bis(4-diethylaminophenyl)vinyl]-6-dimethylaminophthalide and the
additive is comprised of benzoyl leucomethylene blue. In a further
embodiment the additive is placed into a protective layer (18) that
overlies the color-forming layer.