The present invention relates to a photochromic ink, the process for its preparation which is based on a spiropyran powder obtainable by melting, cooling and crushing, and to a new form of a spiropyran obtainable thereby. The wrapping apparatus includes a shuttle that moves along the inner periphery of a track dispensing a wrapping material. Preferably, a plurality of multiple-mirror combinations is provided on a sheet, each combination forming a pattern which is repeated regularly, the patterns all having identical shapes and sizes. The shifted data bits are tested for alignment.