Color and sunlight degradation of materials

[Rick]

Over 30 years ago I was a young engineer working in support of various physics experiments, some of which were laser research projects. Laser optical layouts were set ups were confined to dedicated rooms secured so as to prevent inadvertent exposure to high power beams which could cause eye damage.

Although it was standard procedure to wear protective eye covers with proper lenses the white walls were usually painted with large black stripes at eye level around the room. The idea was that if some scattering of the laser beam should occur the black stripe would absorb the light energy and not cause further reflection. This worked, especially with the high power red laser beams.

When lasers were developed which generated light in the ultra-violet range (beyond the frequency respose of human eyes) special optical "translators" were worn to observe the beam. Much to the surprise of the physicists it was discovered that ultra-violet light reflected off of the black stripe like a mirror! Upon reflection (I like stupid puns) the experimenters realized that black was a good absorber of infra-red energy and a reflector to ultra-violet and the obverse was true for white.

That general concept is why materials normally degraded by long exposure to sunlight are made of light colored materials (like plastics and cloths). It may seem counterintuitive to us to do so yet if you use black plastic tie wraps above deck you will notice a much longer life than if you use the white or clear ones. Boaters have known that the black, blue and dark Sunbrella materials last longer than the lighter colors which is why you don't see very many variations to that color "theme".

Yes, black makes for a hot item from the absorption of the infra-red energy from the sun but the degradation from heat is insignificant compared to the degradation caused by the very short wave-length ultra-violet energy which generates molecular breakdown. Black caulking lasts longer than white...have you noticed? White items may last longer if coated with a sacrificail layer of some white paint heavily loaded with titanium dioxide, for example. There are some clear ultra-violet shields yet, in general, they are not chemically available to us in a form useful to coat things like white canvas, plastic, etc. I'm sure that this will change.

Black, cool, huh?

Regards,
Rick

[Alan Wheeler]

Wow!. That was fantastic Rick. I have wondered for years why Black lasts longer outdoors, when it supposedly absorbed everything. Now that makes perfect sense. Thankyou.
Mate, this is why I love certain BB's. The wealth of experiance found is just plain astronomical. I can also be found on a Live Audio BB,(about 10years) and once again, the experiance is unbelievable. Everyone from NASA through to guys that work with the President and Pope, to guy's that just turn up to work with their lunch box.

[Strygaldwir]

Rick;

Thank you. I do so enjoy lucid and on point discussions!



Keith

[Richhh]

Yup, White dacron degrades much faster in UV exposure than 'tanbark' .... now you know why serious cruisers have brown sails.
Ditto with nylon ripstop spinnaker cloth.... its always the white that 'goes' and long before the colored panels, black being the last to go.
Go to any auto junkyard and see what colors are still good after many years of exposure .... yup, its black.

;-)