h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

When a faded black t-shirt is wet it appears less faded than it is. Why?

I assume it's something to do with refraction/reflection and things like that, but it's puzzled me for a long time.

Traveller in Time not sure
"Guess it has to do with the fluffyness of the fibers.

dry:
////////////////////////////////// faded colour in the tiny fibers
---------------------------------- more solid colour in the thread

wet:
__________________________________ tiny fibers flat on the thread, nearly invisible
---------------------------------- more solid colour in the thread


Pebbles do the same, they have beautiful colour when wet but the cracks show up grey when dry. "

Or in other words dry things have a greater surface area and reflect more light?

Isn't the process more dominated by scattering rather than reflection?

A wetted material presents a more uniform optical surface, due largely to surface tension effects which reduce the scattering effect of small irregularities. This filtering out of the 'white noise' allows us to see the less luminous intrinsic coloration that is always there but greatly obscured during dry conditions.

That's my guess, anyway

Traveller in Time thinking
"Fog appears white, snow appears white, liquid or gaseous water seems colourless.

Actually thought it had to do with refraction on the surfaces for water that is.

The fluff on clothes is bleached a little"

This conversation has been done before - more or less...

F2124165?thread=689368

Or even
F2124165?thread=689380
and
F2124165?thread=700691

The second of those two came up with this link
http://www.straightdope.com/classics/a3_356a.html
which seems to hold up the scattering theory that Seth mentioned.