Gloss is often difficult to describe, let alone measure, and everyone has their own idea of what "gloss‟ is. It‟s an important factor in quantifying the appearance of a product in many industries from plastics to cosmetics - in fact, anywhere the perception of a product is dependent on its reflective properties.
Gloss is an optical property related to the reflection of highlights - the ability of a surface to reflect light in a particular direction. Measuring it has to take into account a number of elements: the refractive index of the material, the angle of incident light and the surface topography. Essentially, it involves comparing the amount of reflected light from a sample, to that reflected from a black glass calibration standard with a defined refractive index. Several different angles are used for measurement, with incident angles of 20, 60, and 85 degrees the most common (for high, medium and low gloss surfaces respectively), but other angles are used for specific applications, such as 75 degrees for plastic film, and 45 degrees for vinyl siding.
The increasing importance of being able to quantify gloss, when in the past it has been simply subjective, has led to a large number of different instruments being produced to measure gloss, but these are often sold, and calibrated, without traceability. That‟s a problem for companies with (sometimes very specific) obligations under standardized quality management systems such as ISO 9001:2008, or the more prescriptive and industry-related SAE AS9100 / AECMA prEN 9100, in the aerospace sector, or ISO/TS 16949:2009, in the automotive sector, for example. Accredited calibration of instruments is becoming crucial as new requirements specify that traceability and competent measurements are demonstrated by accreditation to ISO/lEC 17025:2005.
Aerospace Metrology & Electromechanical Calibration Ltd (AMECaL) is the company setting the standard for others to follow, building a reputation, and gaining a unique position in the UK, by being awarded the only ISO 17025 accreditation for gloss measurements (and meeting ISO/lEC 17025:2005).
Based in Newcastle upon Tyne, AMECaL has spent four years researching and developing a method of calibration relating to optical gloss measurement. The emergence of an accredited laboratory able to calibrate both the instruments and reference standards will ensure that many more of these instruments can, and will, be calibrated against measurement standards traceable to internat