Optically Variable Magnetic Ink (SPARK®, OVMI)
Dynamic color-shifting ink developed by the Swiss company SICPA. Pigments of the magnetic ink used in SPARK® are oriented with the help of the magnetic field so that when the angle of illumination or observation changes, the image changes its color. As result, there is a rolling-bar dynamic effect (a beam of light moving diagonally across the image). Is applied by screen printing, contains ferromagnetic pigments.
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Fig. 1. Ireland. Official passport issued in 2013:
a — page spread (front endpaper – page 1). Paper substrate (front endpaper), polymer substrate (page 1); b — the same. Zoomed fragment. SPARK® security feature. Nontransparent metallized pigments; c, d, e, f — the same. A rolling-bar dynamic effect (a beam of light moving diagonally across the image). Color shifting. View at different angles of observation