Combifluo™

Type

Machine Readable Pattern (MR-UV) — security thread with Cleartext-style demetallised patterns and an alternation of fluorescent colours along the front, mirrored by an inverted alternation along the back, producing at least a third distinct fluorescent colour at the transparent pattern regions when illuminated under UV.

Overview

Combifluo™ is a fluorescent security thread developed by VHP Security Paper, the Dutch state security paper mill in Apeldoorn (operating under the VHPSP brand and tracing its banknote paper-making heritage to the Joh. Enschedé lineage). The thread combines two complementary security mechanisms in a single component: a Cleartext-style demetallised pattern visible in transmission, and a UV-fluorescent colour scheme that is structured to deliver three distinct fluorescent colours from only two physical fluorescent inks. The thread carries an alternating fluorescent colour pattern on its front face — for example, a sequence of red, green, red, green — and an inverted alternation of the same colours on its back face, so where red appears on the front, green appears on the back, and vice versa. At the transparent demetallised cleartext patterns, the front and back colours overlay in transmission, producing at least one additional distinct fluorescent colour. The result is a UV-active feature with three perceived colours and a tightly registered front-to-back relationship that cannot be reproduced through commercially available fluorescent printing.

Technology & Effects

The Combifluo™ effect rests on three coordinated structural elements. First, a thread carrier carrying alternating fluorescent ink bands on its front face. Second, an inverted alternation of the same fluorescent inks on the back face, precisely registered to the front pattern. Third, demetallised Cleartext-style patterns that create transparent windows through the thread, allowing transmitted UV-induced fluorescence from the back face to combine with the front face emissions in those regions. The result delivers three distinct UV-fluorescent colours — the two original ink emissions visible directly on each face, and at least one additional combined colour visible at the transparent pattern regions when the banknote is illuminated under UV in a manner that allows transmitted light to interact with both faces. The Cleartext patterns themselves provide a complementary daylight authentication cue, visible in transmission as legible text or design elements. Effect types: MR-UV (primary), Demetallised (secondary, via the Cleartext patterns).

Form Factors & Application

Combifluo™ is supplied as an embedded security thread, integrated into VHP banknote paper during paper formation rather than applied at the printing stage. Public deployments document a 1.2 mm thread width on the Oman ½ rial and 100 baisa banknotes, indicating the thread is suited to narrow-thread embedded formats rather than super-wide windowed configurations. As a VHP-paper-integrated feature, it is naturally compatible with VHP's other paper-based offerings (PIXEL™ and HD VISION™ watermarks, Diamone™ and Highlink™ durability substrates, Bioguard™ antimicrobial treatment), and sits in VHP's security thread portfolio alongside Picture Thread™ (3D portraits via fine-dot tonal variation), Pulsar™ (micro-optic moving colour-shift), Dual Track™ (wide windowed two-track machine-readable thread), and Starsheen™ (liquid-crystal colour-shift).

Security Levels

• Level 1 (public): Cleartext patterns visible in transmission as a daylight authentication cue, providing immediate verification without equipment.
• Level 2 (cash handler): Three distinct fluorescent colours under UV illumination, derived from a two-ink front/back inverted alternation registered through transparent Cleartext windows. The combination of front-back registration accuracy, demetallisation precision, and the perceived third-colour effect resists reproduction using commercial fluorescent printing or photocopying technologies.

Notable Deployments

• Oman — ½ rial and 100 baisa banknotes (Central Bank of Oman, 2020 series): both denominations carry an embedded 1.2 mm Combifluo™ thread with the front/back alternating fluorescent colour pattern and the third-colour transmission effect. The Oman series also features Avalon Tri Fluo™ printing throughout (Oberthur Fiduciaire's first deployment of that ink on circulating banknotes), Ultra™ post-print varnish, and — on the 1 rial — Oberthur Fiduciaire's Pulsar™ thread. The series received recognition at HSP EMEA awards for design and innovation.