Abstract: A barcode encodes information in a digital format readable by an optical instrument. Conventionally, barcodes comprise a machine readable portion and a human readable portion, the portions being physically separate. The invention is the use of an ink for the machine readable portion which is visible to the barcode reader instrument when exposed to ultra-violet light or to ultra-violet light. The human readable information may correspond to the machine readable information or it may differ. The respective absorption spectra of the machine readable portion and the human readable portion have no significant overlap and the machine readable portion has no significant absorption in the visible region of the spectrum.