Micom Laboratories can now evaluate your pigments’ reaction to sunlight filtered through glass with ASTM D4303
Micom Laboratories is pleased to announce that it now offers the ASTM D4303 test as part of its offering for Coating testing services. ASTM D4303 is aimed at simulating daylight filtered through glass to induce color changes of the pigments used in artists’ paints. Indeed, knowledge of the retention of a pigment’s chromatic properties over a long period of time is crucial. Depending on the quality and nature of the materials which have gone into a pigment’s construction as well as its environment, a painting may age well or poorly. Furthermore, different pigments are naturally sensitive to UV light. This is why many masterpieces are behind glass windows and the usage of camera flashes is not allowed as even indoor lighting and camera flashes can alter the pigments’ visual properties.
By undertaking a weathering test on different pigments, it will be possible to select specific colorants best suited for certain applications based on their performance. These pigments include oil, resin-oil, acrylic, emulsion, alkyd, watercolor paints as well as gouache paints. To quantify the changes in color, color measurements such as ASTM D2244 will be made before and after the exposure.
In order to quantify the difference between 2 colors, a formula was established and is called DE (Delta E). The formula used to determine the distance between color 1 (L1*, a1*, b1*) and color 2 (L2*, a2*, b2*) is:
DE = [ (L2*‐ L1*)2 + (a2*‐ a1*)2 + (b2*‐ b1*)2 ] 0.5
L*.a*.b*. coordinates refer to the coordinates of the color in the CIELAB 76 sphere. It is actually a three‐dimensional space where the L* axis represents the “lightness” of the color (Black to white), a* is the green‐red axis and b* isthe blue‐yellow axis. L* axis goes from 0 (darkest black) to 100 (brightest white), a* goes from ‐100 (green) to + 100 (red), b* goes from ‐100 (blue) to + 100 (yellow).
It was found that the Just Noticeable Difference (JND) is, for most people, at DE =2.3. This means that the magnitude of difference between 2 colors must be 2.3 or more to be noticed by the naked eye. Over the years, some industries came up with their own JND value based on specific needs and applications. The 2.3 value is, however, still widely used as the JND.
Other DE scales can be found in the literature:
0,0 < DE ≤ 0,5: No color difference
0,5 < DE ≤ 1,0: Difference only perceivable by experienced observers
1,0 < DE ≤ 2,0: Minimal color difference
2,0 < DE ≤ 4,0: Perceivable color difference
4,0 < DE ≤ 5,0: Significant color difference
5 < DE: Different colors
0 < DE ≤ 1: Observer does not notice the difference
1 < DE ≤ 2: Only experienced observer can notice the difference
2 < DE ≤ 3.5: Unexperienced observer can notice the difference
3.5 < DE ≤ 5: Clear difference in color is noticed
5 < DE: Observer notices two different colors
Before undertaking testing, it is important to choose at least two of the four methods that ASTM D4303 englobes. Depending on the test method, the type of exposures changes. These include: natural daylight, fluorescent UV lamps (e.g.: ASTM G154) or xenon-arc UV light sources (e.g.: ASTM G155). Both of the UV light sources mentioned are used to predict the effect of sunlight exposure, either outdoor or indoor, on your product on an accelerated basis. To determine which is best suited for you specific needs, please see; The Difference between ASTM G154 and G155 and which is Right for you.
Micom offers polymer testing services for a wide selection of material and products. For more information about the ASTM D4329 test, do not hesitate to get in touch with our specialists.
Micom Laboratories is a third party industrial material testing laboratory accredited by the Standards Council of Canada, CGSB, ISTA and many other organizations.
All of the information and opinions contained in this blog are made with the information, and the understanding that we have reviewed at the time of publishing. However, despite our efforts, we do not offer any guarantee of their accuracy, thoroughness of our investigation or validity. The author of this blog is not liable for any inaccuracies or any losses or damages that may result from the use of the information or data contained herein. This blog has not been reviewed or verified for its accuracy by any peer group associates prior to publication.