Fade to Black … and Blue

Printed materials fade to black and blue because black and cyan ink are more resistant to the sun’s short UV waves

When you have a poster, a newspaper, or some other printed material sit in direct sunlight, the colors fade over time and frequently you are left with a mostly black & blue print. Colors fade for a variety of reasons (humidity, the type of paper, the types of inks, the temperature, etc) but exposure to light, and in particular ultraviolet light, is the primary reason.

The electromagnetic spectrum accounts for photons with a variety of wavelengths – from the very short (gamma waves) to very long (radio waves). The portion of the spectrum we can see with our eyes is known as visible light, which accounts for all the colors of the rainbow. Blues and violets are shorter wavelengths than yellows and reds. Sitting just beyond the blues & violets is ultraviolet (UV). While blue and violet are visible, ultraviolet is invisible. UV wavelengths are just a bit shorter than what our eyes can perceive. UV wavelengths are also dangerous.

When ultraviolet waves from the sun hit printed materials their short wavelengths can break the chemical bonds of the colored inks. The more damage to those chemical bonds the less those printed colors are able to continue reflecting the wavelength of their particular color. The typical printing process uses 4 colors: cyan, magenta, yellow, and black. Cyan (blue) reflects the relatively short wavelengths to make the color blue and as such it is better equipped to resist the even shorter wavelengths of UV. What we see as “black” is frequently a dense combination of ink colors (including black ink) and so it takes longer for this combination of inks to fully breakdown (although it will start to shift and lighten in color). Yellow and magenta however are forced to absorb shorter wavelengths and only reflect the longer wavelengths that are their colors. As such, the yellow and magenta in a printed poster tend to fade faster because more ultraviolet light is being absorbed and breaking down the chemical bonds of those inks.

This is why printed materials sitting out in the sun for too long will commonly lose their warmer colors faster than their black and blue colors.

Added bonus: The Earth’s atmosphere blocks a lot of UV waves from the sun, but some still enters our atmosphere. Because the moon’s atmosphere is too weak to block the sun’s ultraviolet waves, the American flags planted on the moon are all white at this point after decades of ultraviolet exposure has faded all of their colors away.