The Look of Luxury

The Challenge

Visual attributes such as colour, gloss, texture, or sparkle combine to give a surface its unique appearance. In products like cosmetics or automotive paint, appearance can have a significant impact on consumer choice.

If there are two cars in a showroom, one coated in a dull, rough paint, and the other bright and glossy, with a hint of metallic sheen, which one would you choose? It’s no surprise then, that manufacturers of special-effect pigments are producing increasingly sophisticated compounds that make products stand out from the crowd.

But there are very few existing measurement standards for surfaces that display novel optical effects. This has ramifications at all stages – during research and development, in discussions on IP protection, around quality control, and in the wider adoption of these surfaces across industry.

The MSL Solution

MSL partnered with seven other national measurement institutes (NMIs) to establish tools and methods, traceable to the International System of Units, to optically characterise a range of novel surfaces. This included glossy materials and goniochromatic paint, which changes colour when illuminated or observed from different directions. For these surfaces, we focused on the measurement of light scattering, and worked with the Czech Metrology Institute to develop a new primary goniospectrophotometer detector.

Goniospectrophotometers can directly measure an object’s bidirectional reflectance distribution function (BRDF) – a factor that precisely defines how a surface scatters light at different wavelengths, making it a key contributor to a surface’s appearance. Our detector has a very wide dynamic range – it can measure light signals of just a few femtowatts (10⁻¹⁵ watt) to tens of microwatts (10^-6 watt). This makes it possible to accurately characterise dark surfaces, which are typically challenging because they scatter so little visible light.

The resulting system – built here in New Zealand – is now one of a small number of traceable goniospectrophotometers in the world. Its unique design offers more flexibility than many other existing systems, and that allows us to make BRDF measurements for our customers’ surfaces in almost any configuration.

The Impact

In industries where the appearance of a product is crucial (e.g., cosmetics), much of the characterisation and quality control is carried out ‘by eye’, making it highly subjective. MSL’s research is changing that. We now have instrumentation that can objectively, and traceably, characterise materials with novel optical properties.

By working alongside other NMIs, we have also developed a common language for the measurement of light scattering. Together, these tools provide industry with a more reliable way to define and control the properties of a surface, whether it’s a glossy coat of paint for a sportscar, or an eyeshadow that sparkles all evening.

Statement

This work began under a joint research project – xDReflect – that involved eight NMIs and twenty industry collaborators. These included Audi, Toyota, BASF, and Saint-Gobain, who will all benefit from our newly-developed techniques.

A follow-on project, called BiRD, is now using results from xDReflect to produce documentary standards for BRDF and new guidelines for gloss measurements, alongside establishing quantifiable definitions for sparkle and graininess.