# Why does cardboard get dark when wet? **URL:** \ **Category:** Factual Questions\ **Created:** [September 11, 2006, 3:30pm UTC](https://boards.straightdope.com/t/why-does-cardboard-get-dark-when-wet/372297 "2006-09-11T15:30:37Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [September 11, 2006, 3:30pm UTC](https://boards.straightdope.com/t/why-does-cardboard-get-dark-when-wet/372297/1 "2006-09-11T15:30:37Z")
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? ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [September 11, 2006, 3:38pm UTC](https://boards.straightdope.com/t/why-does-cardboard-get-dark-when-wet/372297/2 "2006-09-11T15:38:57Z")
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. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [September 11, 2006, 3:42pm UTC](https://boards.straightdope.com/t/why-does-cardboard-get-dark-when-wet/372297/3 "2006-09-11T15:42:30Z")
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. ---
**Author:** ![Kalhoun](https://avatars.discourse-cdn.com/v4/letter/k/3bc359/32.png) [@Kalhoun](https://boards.straightdope.com/u/Kalhoun)\ **Post date:** [September 11, 2006, 4:32pm UTC](https://boards.straightdope.com/t/why-does-cardboard-get-dark-when-wet/372297/4 "2006-09-11T16:32:42Z")
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. ---
**Author:** ![Arjuna34](https://avatars.discourse-cdn.com/v4/letter/a/eb8c5e/32.png) [@Arjuna34](https://boards.straightdope.com/u/Arjuna34)\ **Post date:** [September 11, 2006, 8:13pm UTC](https://boards.straightdope.com/t/why-does-cardboard-get-dark-when-wet/372297/5 "2006-09-11T20:13:18Z")
[QUOTE=Kalhoun] 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. [/QUOTE] Here it is: [Why do wet things look darker than dry things?](http://www.straightdope.com/classics/a3_356a.html) Arjuna34 ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [September 11, 2006, 9:42pm UTC](https://boards.straightdope.com/t/why-does-cardboard-get-dark-when-wet/372297/6 "2006-09-11T21:42:36Z")
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. ---
**Author:** ![danceswithcats](https://avatars.discourse-cdn.com/v4/letter/d/9e8a1a/32.png) [@danceswithcats](https://boards.straightdope.com/u/danceswithcats)\ **Post date:** [September 12, 2006, 8:33am UTC](https://boards.straightdope.com/t/why-does-cardboard-get-dark-when-wet/372297/7 "2006-09-12T08:33:59Z")
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. ---
**Author:** ![danceswithcats](https://avatars.discourse-cdn.com/v4/letter/d/9e8a1a/32.png) [@danceswithcats](https://boards.straightdope.com/u/danceswithcats)\ **Post date:** [September 12, 2006, 8:35am UTC](https://boards.straightdope.com/t/why-does-cardboard-get-dark-when-wet/372297/8 "2006-09-12T08:35:05Z")
typically=dypically too :smack: ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [September 12, 2006, 9:07am UTC](https://boards.straightdope.com/t/why-does-cardboard-get-dark-when-wet/372297/9 "2006-09-12T09:07:17Z")
[QUOTE=danceswithcats] 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. [/QUOTE] 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).