High-Security Smart Glass for Luxury Collections

Introduction

As smart glass OEM manufacturers since 2009, we are often asked if it is possible to combine smart (auto-tinting) interlayers into high-security glass.

The answer is: yes, absolutely!

The main benefits include:

• exclusivity and privacy over the items on display,
• after-hours security (since the smart glass becomes dark by default, hiding the items), and
• a stunning, theatrical presentation to wow your customers and visitors.

This article describes the engineering challenges we have overcome in building high-security, auto-tinting smart glass products.

Smart Glass for Patrimonial Jewellery

One such project we delivered in 2022 was through our parent company ArtRatio for a luxury jewellery house in Paris.

Our customer asked us to build high-security smart glass display cases for a series of patrimonial jewellery exhibitions in Shanghai, Riyadh and Seoul. Since these exhibitions are now over, we can write about them without exposing any details that could compromise security.

For this project, we designed a 20.5 mm thick high-security smart glass stack, featuring a PVB interlayer to ensure compliance to EN 356 (P6B).

The glass also featured a SPD smart glass interlayer that tints under the control of our patented ArtRatio Operating System.

The display cases housed heritage jewellery, including a gold and diamond choker from the Elizabeth Taylor collection and a diamond tiara once belonging to Princess Grace of Monaco. 

Needless to say, the visual effect was stunning:

Multi-Layered Smart Glass

When building high-security smart glass, the best solution is based on a ‘multi-layered sandwich’. This consists of an EVA (ethylene-vinyl acetate) layer to laminate the smart SPD film, and PVB (polyvinyl butyral) to laminate the security glass.

The resulting glass stack design was as follows:

The diagram below shows the SPD smart film in its powered state, where the particles align with the electric field. This gives a visible light transmittance (VLT) of 49%.

We augmented this ambient lighting with directed LED spot lights to create a stunning, high-contrast effect. As you can see in the video at the end of this page, the item appears to float mid-air as the display case slowly becomes transparent.

All timings are configurable via the ArtRatio Operating System intranet.

(The dimensions of the layers in the following diagram are not to proportion).

The diagram below shows the SPD film in its off state, where it blocks light by absorption, since the particles are no longer aligned with the electric field. 

Our control system drives the smart glass and LEDs simultaneously with our timer mechanism, in this case allowing for 30 seconds ‘on’ and 10 seconds ‘off’ (repeatable).

How much does this glass weigh?

This 20.5 mm thick multi-laminate glass (of dimensions 680 x 680 mm) weighed 21kg, which poses some real issues when fitting the glass into a hinged door mechanism. 

On top of that, the display cases were to be installed into a wooden wall, where the glass door needed to open outwards up to 120º. This creates a risk of damage while the curator is installing the items on display.

For this purpose, we built a wooden wall in our workshop to test out the installation, since we were not allowed to travel to Shanghai due to COVID travel restrictions at the time. See the videos at the end of this article.

Smart Glass Lamination

Some types of smart glass, such as Suspended Particle Devices (SPD) smart glass, require lamination only with EVA. 

Alternatives such as PVB contain chemical plasticisers that can dissolve the active emulsion layer of the smart film and damage the Indium Tin Oxide (ITO) transparent conductors during high-pressure processing. 

EVA, on the other hand, is chemically inert and safe. 

The SPD film is laminated with ITO-coated tempered glass and EVA to produce a glazing unit, which we subsequently bonded to a second glass structure using PVB. An alternative, even stronger layer would be SentryGlass (SGP) but was not specified on this project.

Both PVB (and SGP) are thermoplastic resins, known for their optical clarity, binding strength and impact resistance. The PVB side is thus the outer-facing side which hinders brute-force attacks on the glass.

The glass itself is tempered, ensuring resistance to thermal shock, and has low iron content to reduce the greenish tint and improve visibility on the items displayed.

Smart Glass Reflection

We are often asked about anti-reflective (AR) layers on smart glass, but internal reflections within the glass stack itself negate the effects of any AR coatings that might be placed on the glass exterior.

Since the AR coatings are quite expensive, the net result is of minimal benefit. In short, it’s simply not worth the extra cost to the customer.

Below we can find some images and videos of the build process in our workshop in Spain, and of the exhibition in Shanghai.

Conclusion

This article discusses the benefits and engineering issues in building high-security, auto-tinting smart glass to control the visibility of high-valued luxury items. 

The multi-laminate smart glass has to contend with weight issues, and must be designed carefully when installing the glass into hinged doors or frames which can be opened beyond 90º.

The overall external reflectivity of the glass stack is around 12-14% due to the multiple changes in refractive index throughout the complex glass structure, which one cannot negate with simple anti-reflective (AR) coatings. 

This project did not however suffer any complaints due to reflectivity, thanks to the low ambient light levels in the exhibition.

The prime benefit of high-security smart glass is the privacy and exclusivity afforded to the items on display. Also important is security compliance to EN 356 (P6B), a necessary requirement for luxury jewellery collections.