An Introduction to Gloss Measurement
(because we care and we hope you in turn will purchase from us)
1. What is Gloss?
2. What difference in gloss units is visible to the human eye?
3. Why Measure Gloss?
4. How is Gloss Measured?
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1) What is Gloss?
Gloss is an aspect of the visual perception of objects.
Gloss is the attribute of surfaces that causes them to have shiny or lustrous, metallic or mat appearances.
Gloss is a visual impression that is caused when a surface is evaluated. The more direct light is reflected, the more obvious will be the impression of gloss.
Gloss effects are based on the interaction of light with the physical properties of the sample surface. The other influencing component is the physiological evaluation scale. The human eye is still the best tool to evaluate gloss differences. However, the visual surface control is insufficient, because evaluation conditions are not clearly defined, and people see and judge differently
In addition, the subjective perception of appearance is dependent on the personal experience: what is glossy for a paper manufacturer might be dull for an automotive maker. Gloss is measured by focusing on the reflected image and not by focusing on the surface. Eyesight and mood have a decisive role in the visual judgment. Also, important is what our eye is focused on. We evaluate a surface by focusing our eye on a reflected image of a light source. In order to guarantee a reliable and practical quality assurance it is necessary to define appearance with objective, measurable criteria. Accurate characterization of appearance does not only help to control quality, but improves quality and optimizes manufacturing processes.
High Gloss ]
A s mooth and highly polished surfaces reflect images distinctly. The incident light is directly reflected on the surface, i.e. only in the main direction of reflection. The angle of incidence is equal to the angle of reflection.
Semi Gloss ]
O n rough surfaces the light is diffusely scattered in all directions. The image forming qualities are diminished: A reflected object does no longer appear brilliant, but blurred.
The more uniform the light is scattered, the less intense is the reflection in the main direction and the duller the surface will appear.
High and Semi Gloss ]
O ne Gloss meter does double work. The DUAL is a new model from 2007 re-engineered and at a lower price.
Low Gloss or Mat ]
O n very rough surfaces the light is diffusely scattered in all directions. The image forming qualities are much diminished: A reflected object no longer appears brilliant, but almost non-existent.
Measure all three modes Simultaneously ]
W hen one requires measuring all three types of surfaces described above, we have two gloss meters that simultaneously measures all three geometries.
All three modes plus Coating Thickness NFe/Fe ]
O ur gloss meter incorporates all the technological advances into one unit offering a unique package in an economical package. The micro-tri-gloss µ has everything you require in one compact gloss and coating thickness meter.
Measure small rounded objects or small areas ]
2) What difference in gloss units is visible to the human eye?
If two different coatings are measured, what number of gloss units would be detectable by the human eye, how many units would be perceived as significantly different?
When measuring at 60 Degrees these detectable differences depend on the gloss level of the sample, for instance 3.0 GU difference measured on a very matt surface (perhaps 5GU), would be seen by the human eye but on a higher gloss coating (perhaps 60 GU) the difference would be very difficult to notice.
The only way that you can determine tolerances for your products would be experimentally, perhaps preparing printed samples at different gloss levels that you can show to end users of your coatings or internal experts
The other option is to change to a 20/60/85 degree instrument, the 85 degree glossmeter is more sensitive to differences in gloss below 10 GU @ 60º and the 20 Degrees has higher resolution on high gloss coatings (above 70 GU @ 60º). The advantage of using the three angles is that there is more equality to the gloss differences, in our experience a gloss difference of 5 GU, when measured with the correct geometry is just visible to a trained observer.
3) Why measure gloss?
Gloss is an aspect of the visual perception of objects that is as important as colour when considering the psychological impact of products on a consumer. It has been defined as the attribute of surfaces that causes them to have shiny or lustrous, metallic appearance.
The gloss of a surface can be greatly influenced by a number of factors, for example the smoothness achieved during polishing, the amount and type of coating applied or the quality of the substrate. Manufacturers design their products to have maximum appeal- highly reflective car body panels, gloss magazine covers or satin black designer furniture.
It is important therefore that gloss levels are achieved consistently on every product or across different batches of products. Gloss can also be a measure of quality of a surface, for instance a drop in the gloss of a coated surface may indicate problems with its cure- leading to other failures such as poor adhesion or lack of protection for the coated surface.
It is for these reasons that many manufacturing industries monitor the gloss of their products, from cars, printing and furniture to food, pharmaceuticals and consumer electronics.
4) How is gloss measured?
Gloss is measured by shining a known amount of light at a surface and quantifying the reflectance. The angle of the light and the method by which the reflectance is measured are determined by the surface. Gloss is determined using a Gloss Meter which directs a light at a specific angle to the test surface and simultaneously measures the amount of reflection. The type of surface to be measured determines the gloss meter angle to be used and thus the gloss meter model. The intensity is dependent on the material and the angle of illumination. In case of nonmetals (coatings, plastics) the amount of reflected light increases with the increase of the illumination angle. The remaining illuminated light penetrates the material and is absorbed or diffusely scattered dependent on the color.
A glossmeter measures specular reflection. The light intensity is registered over a small range of a pre-defined reflection angle.
The intensity is dependent on the material and the angle of illumination. In case of nonmetals (coatings, plastics) the amount of reflected light increases with the increase of the illumination angle. The remaining illuminated light penetrates the material and is absorbed or diffusely scattered dependent on the color.
Metals have a much higher reflection and are less angle dependent than non metals.
Metals have a much higher reflection and are less angle dependent than non metals. The measurement results of a glossmeter are related to the amount of reflected light from a black glass standard with a defined refractive index, and not to the amount of incident light. The measurement value for this defined standard is equal to 100 gloss units.
Materials with a higher refractive index can have a measurement value above 100 gloss units (GU), e.g. films. In case of transparent materials the measurement value can be increased due to multiple reflections in the bulk of the material. Due to the high reflection capabilities of metals values of up to 2000 GU can be reached. For these applications it is common to document the measurement results in % reflection of the illuminated light. Glossmeters and their handling procedures had to be internationally specified to allow comparison of measurement values. The angle of illumination is of high influence. In order to obtain a clear differentiation over the complete measurement range from high gloss to matte, 3 different geometries, i.e. 3 different ranges, were defined using a 60° gloss meter.
10 to 70
In addition, there are industry specific applications for 45° and 75° measurement geometry. In this case study, 13 samples were visually ranked from matte to high gloss and measured with the 3 specified geometries. In the steep slopes of the curves the differences between the samples can be clearly measured, while in the flat part the measurement geometry no longer correlates with the visual. Gloss measurement for any application, whether you are dealing with specific applications or need a universal solution from high luster to a matte gloss sample or a small curved surface, Imbotec can help through their knowledge and complete line of solutions: