Production
Optically variable ink (OVI)
Tinta OVI
Optically variable ink (OVI) changes colour with the viewing angle — for example, from green to purple. It is a printed OVD, not a holographic foil or a SPARK patch. A counterfeiter who photocopies or prints flat offset does not reproduce that shift. It is checked by tilting the note under a point light, without solvents. If the colour does not move, it is not OVI, even if it shines: that may be iridescent ink or a separate foil.
The millennium 100-yuan carries an optically variable device with the characters 千年, cited in the record beside the Temple of Heaven window. The Churchill £5 combines window, Elizabeth Tower, and BLENHEIM foil; that patch is not asserted here as OVI if the record names it as foil. The Malaysian RM5 and the Canadian $5 use polymer and window effects; each record says what it shows, without copying an advertising leaflet.
On recent Colombian paper there are iridescent inks and threads; a Pick in this case is not labelled OVI if the source does not say so. The glossary keeps iridescent ink, SPARK, and foil anchored on the index, and leaves this article for printed colour-shift and its OVD relative. None of that ink is for sale; it is described on pieces already published.
OVI, foil, and SPARK are sometimes presented as if they were the same; the catalogue does not. This collection names the effect when the record or the source identifies it, and stays silent when it does not. The 100-yuan and the £5 suffice to show a commemorative OVD and a circulating foil, without attributing a colour shift to a Colombian Pick that does not document it.
Examples in the collection
See also: Optically variable device (OVD) , Iridescent / metallic ink , SPARK , Foil patch