A new, invisible to the naked eye and infrared (IR) readable, ink form
ulation based on silicon(IV) 2,3-naphthalocyanine bis(trihexylsilyloxi
de) as colorant is described The ink formulation is based on absorptio
n and reflection of light in the IR, in contrast to the currently empl
oyed mechanism of excitation and fluorescence detection. The ink absor
bs strongly at 790 nm and has highly transmitting characteristics in t
he visible. A good contrast level was obtained with an illumination so
urce emitting at 790 nm. The ink is stable, lightfast and applicable t
o offset printing, and can also be extended to other printing techniqu
es.