Holograms work by grating diffractions. On reducing the grating period to be below wavelengths of visible light, optical absorptions of visible light by surface plasmon resonance emerge. On direct observation, bright colors due to the absorptions can be seen in reflection and in transmission. On oblique observation, the colors become pale and diffractions become distinct. This enables designing different security features for different observation angles.

ColorTrace™ is an optical security technology working by surface plasmon resonance to show colors for naked eyes and under a polarizer. It takes one more step to add appealing kinetics features to the colors and modulated the diffractions to form rainbow hologram.

ColorTrace™ proves the feasibility of a single Al coating for plasmon resonance, instead of noble metals normally studied in literatures. Not only can this be easily combined with various holographic and de-metallized features, but also makes it affordable to end users.