ASTM D3424 - Standard Practice for Evaluating the Relative Lightfastness and Weatherability of Printed Matter:
The ASTM D3424 standard, which was withdrawn in 2020, was a guide for evaluating the lightfastness and weatherability of printed matter. Understanding the operation of this standard is important to appreciate how such evaluations can be conducted today.
Lightfastness refers to the ability of printed colors to resist fading when exposed to light, while weatherability refers to the ability of printed colors to resist degradation due to weather conditions, including exposure to UV radiation, rain, humidity, and extreme temperatures.
The ASTM D3424 standard covered the following methods to evaluate these characteristics:
Method 1 - Daylight behind window glass: This is the most basic form of testing where the printed matter is exposed to daylight behind a window. The protective window glass can filter out certain harmful UV wavelengths, providing a general understanding of how a printed material might perform indoors or in a window display.
Method 2 - Outdoor weathering: In this method, the printed matter is exposed to actual outdoor conditions without any cover. This method tests the resilience of the print to real-world conditions such as sunlight, rain, and temperature fluctuations.
Method 3 - Xenon-arc apparatus with window glass filters: This is an accelerated testing procedure that uses a xenon-arc lamp. This lamp produces light that closely resembles natural daylight. When combined with window glass filters, it simulates the exposure conditions of Method 1, but at an accelerated rate.
Method 4 - Xenon-arc apparatus with water spray and daylight filters: This method builds upon Method 3 by adding a water spray feature to mimic natural weather conditions such as rain and humidity. The daylight filters in this method simulate outdoor weathering.
Method 7 - Fluorescent lamp apparatus to simulate indoor fluorescent lighting in combination with window-filtered daylight: This test simulates conditions in an indoor environment where the printed matter is exposed to a combination of fluorescent lighting and daylight filtered through a window.
Method 8 - Fluorescent lamp apparatus operating with fluorescent cool white lamps: This is another indoor testing method where the printed material is subjected to lighting conditions created by fluorescent cool white lamps.
These testing methods were used to evaluate the ability of printed matter to resist fading and weathering. The results could be used to guide the selection of appropriate printing materials for specific use cases and to validate the quality of printed products.
It is important to note that lightfastness and weatherability depend not only on the type of ink used but also on other factors such as the substrate (the material on which printing is done), the thickness of the print, and the printed area.