In fact, why do lots of things get darker when wet? I think the answer probably has something to do with water absorbing light as it travels through it, but the layers of water seem to be so thin that I’m not liking that reasoning. Since we can see through a thick fish tank without its appreciably darkening the light coming through, I’m wondering about this phenomenon. I couldn’t find any previous threads, although it seems that this is the type of question that may have appeared here before. And I didn’t find it in my four Dope books. If the Master has dealt with it, I haven’t found it. I know that there are a couple guys here who work in the spectacles industry and know a whole hell of a lot about light. Dopers? Any help?
Dry collections of fibres disperse or scatter light quite effectively; adding water makes the surface layer more transparent, so instead of being scattered at the surface, the light penetrates further into the material, where it is absorbed (well, more of it).
That’s my (not so WA)G, anyway.
And the more I think about it, the more I think the water disperses the reflected light that bounces out from the surface. More light dispersed = less light coming directly to us.
Cecil did a column on this, I think. I don’t have time to look it up, but it’s in there somewhere. Very interesting.
Ok. Thanks - I couldn’t find that for some reason. I claim that Mangetout and I, in some sort of combined version, have stated what the Master said. Mangetout first.
Just to upset the theory-cart: paint of the latex and alkyd variety will dypically dry to a darker shade than that evidenced when applied.
typically=dypically too :smack:
I think this is similar to the white-dries-clear effect of PVA glue; when wet, it’s an emulsion that scatters light effectively; when dry, it’s a layer of polymers (or something).