What does an OVI pigment look like at microscopic level?

Each particle is a miniature optical stack, typically three layers: a highly reflective metal base (aluminium or chrome), a transparent dielectric spacer (such as MgF2) that sets the interference wavelength, and a semi-transparent partial reflector on top that creates multiple internal reflections.

Why does the colour change when the viewing angle changes?

In one sentence: viewing angle changes, optical path difference changes, the enhanced wavelength changes, so the colour changes. Light reflecting off several interfaces interferes with itself, and different wavelengths are reinforced or cancelled at different angles of incidence, producing interference colour that varies continuously with angle.

What is the key metric for OVI security performance?

The colour-contrast between the two viewing angles. A high-contrast pair is easy to recognise in daylight with no equipment at all.

How does OVI pigment particle size affect printing?

OVI pigment is relatively coarse, typically 10 to 30 microns, which places specific demands on process. Common processes are gravure for banknote-grade work, screen for the widest use on spirits, tobacco, labels and bottles, flexo for large continuous areas, and pad printing for small or irregular surfaces. Mesh or anilox parameters, drying method and substrate all have to be considered together.

Where is OVI best applied?

High-security documents such as banknotes, passports and ID cards; tax stamps, invoices and securities; premium spirits, tobacco, cosmetics and luxury packaging; security labels, seals and hang tags; and brand-authorisation marks and commemorative items.

OVI Optically Variable Ink Technology Guide

SJH OVI chameleon ink (copper-green): color shifts with viewing angle on glass substrate — magnetic OVI application demo.

Optically Variable Ink (OVI), commonly called “chameleon ink” in the industry, is a security ink based on thin-film optical interference. Its defining feature: the printed image visibly changes color with viewing angle — one color viewed straight-on, another when tilted, much like a chameleon shifting its body color.

Because this angle-dependent color effect cannot be reproduced by photocopying, scanning or photography, OVI is widely recognized as one of the highest-barrier overt security features, used on banknotes, passports, tax stamps and premium packaging.

1. How It Works: Thin-Film Optical Interference

The heart of OVI lies in multilayer thin-film interference (MLI) pigments. Each particle is a microscopic optical stack with a typical three-layer structure:

Base layer: highly reflective metal (e.g. aluminum/chromium) — strong reflective base
Spacer layer: transparent dielectric (e.g. magnesium fluoride MgF2) — determines the interference wavelength
Top layer: semi-transparent partial reflector — creates multi-reflection and interference

When visible light strikes the pigment, rays are reflected at multiple interfaces and interfere. Different wavelengths are enhanced or cancelled at different incidence angles, producing a continuously varying interference color.

In one sentence: angle changes → optical path difference changes → the reinforced wavelength changes → the color changes.

2. Common Color-Shift Pairs

Green to Blue
Gold to Green
Purple to Green
Red to Green
Cyan to Purple
Green to Purple

High-contrast pairs are instantly recognizable under natural light with no equipment.

3. Why OVI Is Extremely Hard to Counterfeit

Cannot be copied: scanning and photocopying capture a single viewing angle and cannot capture the dynamic color change.
High production barrier: vacuum deposition requires dedicated high-vacuum coating equipment and precise film-thickness control.
Controlled raw materials: high-grade OVI pigments come from very few vendors (e.g. SICPA) under tight control.
Democratized verification: anyone can tilt the product and verify authenticity — a public, self-policing security mechanism.

4. Printing Processes

Gravure: banknote-grade — e.g. early Euro denomination numerals.
Screen printing: the most common — for tobacco/alcohol packaging, security labels, bottle decoration.
Flexo: for large continuous areas.
Pad printing: for small, irregular surfaces.

5. Applications

Banknotes, passports, ID documents
Tax stamps, invoices, securities
Premium tobacco, alcohol, cosmetics and luxury packaging
Security labels, tamper seals, hang tags
Brand licensing marks, collectibles

6. SJH OVI Chameleon Ink Solutions

SJH Ink offers a mature OVI chameleon ink series: multiple color-shift pairs, adapted for offset, gravure, screen, flexo and pad printing, combinable with UV-invisible and IR-excited series for multi-layer security; custom formulations supported.

About SJH Ink

Shenzhen Sojhonink Co., Ltd. (est. 2002, 14 Fuxing Road, Pinghu, Longgang District, Shenzhen) specializes in OVI, UV invisible, thermochromic and IR excitation inks. Free printed proofs. Tel 13510998453, www.sjhink.com.

Optically Variable Ink (OVI): How the Chameleon Security Ink Shifts Color