The Science of Gloss: Understanding its Measurement and Application in Automotive Detailing

By: Jay Broom, Marketing Specialist, and Kelly Harris, Global Director of Training, Lake Country Manufacturing, Inc.

Gloss is a fundamental characteristic that plays a significant role in our perception of the visual appearance of objects. We all know perfectly polished paint is a thing of beauty, but let’s delve into the technical definition of gloss, discuss the measurement of gloss on automotive paint, examine the standardization (or lack thereof) in determining units of gloss using digital gloss meters, and finally, analyze the practical utility of gloss meters for professional auto detailers.

What is ‘Gloss’?

Gloss can be defined as the optical property of a surface that relates to the interaction of light with that surface. A glossy surface reflects a high percentage of incident light, resulting in a bright and shiny appearance and sharp, wet-looking reflections. In contrast, a matte or corrupted surface reflects a lower percentage of light, giving a more diffused, less reflective appearance. Mirrors can sharply reflect almost 100% of incident light, hence “mirror finish” is a commonly used description of attractive, highly glossy paintwork.

Measuring Gloss on Automotive Paintwork

To quantify gloss, digital instruments called gloss meters are used. These devices measure the amount of reflected light at a specific angle, typically 20°, 60°, or 85°. The angle of measurement determines the type of gloss being assessed, such as distinctness of image (DOI) or specular gloss. Automotive paint is often evaluated at a 60° angle, as it provides a good balance between overall gloss and the ability to hide surface imperfections.

Gloss meters use a light source, a detector, and sophisticated algorithms to determine the gloss value of a surface. When the gloss meter emits a beam of light onto the painted surface, the detector measures the intensity of the reflected light (from a very specific point on the painted surface). This measurement is then converted into gloss units (GU) or gloss values, which provide a numerical representation of the surface gloss.

Are Gloss Measurements Standardized?

Organizations such as ASTM International (American Society for Testing and Materials) and ISO (International Organization for Standardization) have developed guidelines and standards to ensure consistency and comparability of gloss measurements. However, while gloss meters provide a standardized method for measuring gloss, there is a lack of universal standardization when it comes to gloss units. Manufacturers may utilize different scales, making it challenging to compare gloss values obtained from different gloss meters accurately. The most common units used include Gloss Units (GU), Gloss Points (GP), and Percent Gloss (%G).

Do Detailers Need to Use Gloss Meters?

Gloss meters can serve as valuable tools for professional auto detailers, allowing them to measure and evaluate the quality of their work in a convincing, methodological way. By quantifying the gloss levels before and after detailing processes, such as polishing or waxing, detailers can objectively assess the effectiveness of their techniques and products. Gloss meters enable them to provide measured results to their clients that point to a high standard of quality in their work — however, there are several pitfalls with reliance on digital gloss meters.

By taking measurements from specific points on paintwork surfaces, gloss meters may not provide precise readings to compare a before and after situation unless great care has been taken to measure the same pinpoint of paintwork each time. It’s also worth noting that gloss meter readings may not necessarily align with what the human eye identifies. Here are two examples:

• The effects of fillers, silicone, and oils on paintwork that is ‘truly’ in poor condition can cause misleading results; similarly, the brightness and viewing angle of certain light sources may reveal such defects as rotary holograms clearly. So, regardless of how big an improvement the gloss meter says you‘ve made, the actual observed result may not be cause for celebration. 
• A gloss meter may give hugely different readings when comparing dull, swirly paint with paintwork that has been buffed heavily; however, as the margins close through subsequent refining stages, the readings obtained by a gloss meter may become so negligibly separate that even though the human eye can see, for example, the difference between a faint DA cutting haze and a fully refined surface, the gloss meter may barely detect the difference — if at all.

In conclusion, gloss meters should not be the sole determinant of a surface's aesthetic appeal. Professional auto detailers should consider gloss measurements as one part of their overall assessment, but only when combined with their expertise in visual inspection, experience, and customer feedback.  

Until next time – happy polishing!

Jay @ Lake Country

IG: /jaybroomdetailing

FB: /jay.broom.detailing 

*This article was provided by Lake Country Manufacturing, Inc., an IDA Diamond Sponsor. It does not constitute an endorsement, guarantee, warranty, or recommendation by the IDA. The IDA makes no representation or warranties about any information contained herein.