Sun Fading Paint Degradation Measured

by William Rice

 The UV radiation resistance, of an industrial protective paint or coating, to sunlight degradation is one of the most important performance issues of critical concern to buyers of industrial protective coatings. How the effects of that UV exposure are measured in industrial protective paints or coatings is the subject of this article.

Probably the most obvious industrial protective paint or coating performance issue is sunlight fade resistance.This is separated  into color loss, chalking and loss of gloss. What ability does the industrial paint or coating have to resist  UV sunlight from decomposition of the paint's or coating's pigments? How does the industrial protective paint or coating keep the pigments from becoming a lighter color? Most importantly, how does the industrial protective paint or coating preserve the aesthetic appearance of the surface to which it is applied?

 Color Loss Or Fade

The extent of color loss of a protective coating depends on five basic factors: the amount of solar sunlight UV radiation exposure, the type of pigment (whether architectural, industrial, or automotive grade), the pigment's color,  the type of resin or resin polymers and the types of coating additives used (such as ultraviolet light absorbers UVA's, hindered amine light stabilizers HALS, or nano-particles of titanium dioxide or zinc oxide)  in formulating the industrial protective paint or coating. Maximum colorfast pigment combined with optimum UV stable resin(s) or polymers is the objective. (See article Sun Also Destroys).  

How Color Loss Is Measured

Three factors go into what makes up color; the chroma, light, and hue. Chroma is how intense that color is. Lightness refers to the degree of lightness or darkness of the color. And, Hue is what color it is perceived to be. The change in color is measured by a mathematical equation and is expressed as a change in what is termed the "Delta E". Most warranties on architectural and industrial coatings have a color difference of a certain Delta E to be covered. Most people (not color blind) are able to tell a color difference of Delta E 2 to 3 if the samples are held up side to side. A color difference ranked as Delta E 4 to 5 are easy to remember because they are so extreme. The problem is most warranties only apply if the Delta E change is 12 to 15. This is like a fire engine red fading to pink. Remember that the next time you are considering a product that has a "no fade" warranty. Read very carefully what the warranty really says in the fine type.


After long term exposure to UV sunlight solar radiation, industrial protective paints or coatings will develop a loose white substance called chalk. Chalk is what's left behind when some of the resin and pigment are broken down by UV sunlight solar radiation exposure. The "white" chalk makes the underlying color look lighter and even dull. It's quite easy on first examination to mistake chalking (which is somewhat reversible) for true fading (which is permanent) color loss. But, washing and wiping the architectural or industrial coating's surface will remove the chalking and restore a good deal of the color. Rating the degree of chalking is a numerical standard of 2, 4, 6, 8 or 10 with 10 being no chalk wiping off.

Note: One excellent way of determining whether a surface is clean enough for a industrial protective paint or coating to be applied to it,  is to wipe a clean white cloth across the surface and if no color comes off, it is clean. Obviously, if the surface is white, the cloth should be of a darker color with no white coming off. For our restoration and protection clearcoat, it's ready for the faded surface that's left to be restored. (See Vivilon Application Instructions).

Gloss Retention

Gloss has been defined as the ability to reflect without any scattering of light. This reflecting Gloss retention on a architectural or industrial protective coating is measured naturally (I kid you not, as Jack Paar used to say) by an instrument called a  glossometer or gloss meter. These gloss meters read gloss at 85, 60 and 20 degrees by shining at the surface a known amount of light and then measuring the reflectance. Light obeys the law of reflection, that the angle of reflection equals the angle of incidence. Thus, a light shined at a 20 degree angle (angle of incidence to the surface) will be reflected at the same angle. A light that reflects according to the law of reflection is called specular reflection (because of its mirror like nature) as opposed to light which is scattered and called a diffuse reflection. There are a number of reasons for a diffuse reflection. One of them, applicable to coatings, is the scattering caused by a rough surface or rough surface profile (see Why Paints Fade and How To Restore Gelcoat  for coating context).

In the diagram below, the different angles that gloss is measured at are depicted. The 85 is for measuring low gloss (satin) or semi-gloss finishes. A 60 angle measures high gloss materials like paints or coatings on metal. And, a 20 angle measures super high gloss like coatings on polished metal. To put all this in perspective, have you ever looked down the side of a truck or boat almost parallel to the surface. That is what an 85 measurement is like. And, looking down the side did you see what looked like a quite shiny (glossy) surface that wasn't there when you instead looked at the truck or boat almost head on (perpendicular or almost 20) and saw no shine or gloss. This is why each finish has a different gloss reading to accurately measure that coating. The test gloss numbers would simply lose their meaning if a super high gloss was measured by an 85 test or vice versa.

Hopefully, you know have a better idea of how a protective industrial paint or coating's ability to withstand UV radiation degradation from weathering is measured.