docholliday wrote:
On Jan 10, 2:15 am, The Natural Philosopher
wrote:
Newshound wrote:
On 08/01/2012 21:03, Bramblestick wrote:
Just noticed this strange thing!
For the last 12 years, we've had an aneroid barometer hanging in the
hall - it's probably 1930's by the look of it, and the top half of the
dial is printed in black text, and the bottom in red. I've just noticed
the the bottom half has disappeared! If you look at it from an oblique
angle, you can see the print, but it has faded to nothing!. The device
is in a really dark nook, getting no natural light, and for at least the
last 5 years the area is lit 24/7 by a lamp on a bureau - some 18" away
(Philips compact fluorescent for the last 3 years or so). The lamp has a
fabric shade, and the barometer's dial has a glass cover. It's not
something that I look at in detail every day - I've got the internet for
the weather ;-), but I know that I calibrated it a couple of years ago &
didn't notice any problem..
Any insight?
Cheers, Bramblestick
Others have mentioned UV, but some red inks as found in hand drawn maps,
legal documents, etc. fade faster than the black even in the absence of
light. Probably oxidation.
I printed some inkjet decals and left em on a window sill half obscured
by an ornament.

In the shade they stayed red. In sunlight with UV they were wiped out
red wise.

Its something in that particular red dye.- Hide quoted text -

- Show quoted text -

I seem to remember that just about all the bright red pigments and
dyes that you could make reasonably inexpensive paints and printing
inks from were prone to fading in light, or chemically by reacting
with air, or toxic - or some combination of the three, although this
may have improved in recent years. On the other hand, carbon black was
(and is) commonly used as the pigment in black paints and printing
inks, and is very stable, as are various black, brown and yellow
pigments based on Iron oxide. I've seen lots of dials where red
printing has faded while the black is as good as new, even when they
were only in indirect sunshine - so a fluorescent lamp only 18 inches
away could possibly have the same effect.

Reds are notorious for UV fading.

Especially organic pigments.

http://www.paintmaking.com/red.htm

Its no bad idea to put a UV barrier lacquer over reds..apparently.