# A Question About Chewing Gum **URL:** \ **Category:** Factual Questions\ **Created:** [October 1, 2004, 1:12pm UTC](https://boards.straightdope.com/t/a-question-about-chewing-gum/267015 "2004-10-01T13:12:41Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![Tir\_Tinuviel](https://avatars.discourse-cdn.com/v4/letter/t/bc79bd/32.png) [@Tir\_Tinuviel](https://boards.straightdope.com/u/Tir_Tinuviel)\ **Post date:** [October 1, 2004, 1:12pm UTC](https://boards.straightdope.com/t/a-question-about-chewing-gum/267015/1 "2004-10-01T13:12:41Z")
Why does discarded chewing gum turn black on the pavement, but remain white on the road? ---
**Author:** ![Sigene](https://avatars.discourse-cdn.com/v4/letter/s/df788c/32.png) [@Sigene](https://boards.straightdope.com/u/Sigene)\ **Post date:** [October 1, 2004, 1:33pm UTC](https://boards.straightdope.com/t/a-question-about-chewing-gum/267015/2 "2004-10-01T13:33:21Z")
Holy Cow!!! A question for the ages! I have no idea of the answer, but this definitely one that Cecil himself needs to address ---
**Author:** ![Shagnasty](https://avatars.discourse-cdn.com/v4/letter/s/9dc877/32.png) [@Shagnasty](https://boards.straightdope.com/u/Shagnasty)\ **Post date:** [October 1, 2004, 1:39pm UTC](https://boards.straightdope.com/t/a-question-about-chewing-gum/267015/3 "2004-10-01T13:39:44Z")
I am not completely clear on what you are asking. Are you asking about chewing gum stuck to an asphalt rather than a concrete service? If so, asphalt has a lot of black residue that gets distributed over anything that is on it for a period of time by cars driving over it etc. Concrete has only dirt. ---
**Author:** ![Tir\_Tinuviel](https://avatars.discourse-cdn.com/v4/letter/t/bc79bd/32.png) [@Tir\_Tinuviel](https://boards.straightdope.com/u/Tir_Tinuviel)\ **Post date:** [October 1, 2004, 1:50pm UTC](https://boards.straightdope.com/t/a-question-about-chewing-gum/267015/4 "2004-10-01T13:50:28Z")
But **Shagnasty** , that is the problem. The chewing gum in the road being driven over by cars remains white. The chewing gum on the pavement being walked over turns black almost straight away. ---
**Author:** ![pokey](https://avatars.discourse-cdn.com/v4/letter/p/ebca7d/32.png) [@pokey](https://boards.straightdope.com/u/pokey)\ **Post date:** [October 1, 2004, 3:09pm UTC](https://boards.straightdope.com/t/a-question-about-chewing-gum/267015/5 "2004-10-01T15:09:35Z")
I’ve never really looked at the gum on the road but maybe it is like this [optical illusion](http://www.wordiq.com/definition/Optical_illusion) where something that grey can look totally different depending on the contrast. Since asphalt is dark grey it is like the dark grey square in the picture and since the sidewalk is light grey it is like the light square. If you look at the picture in that link it looks like a HUGE difference and you can’t even believe they are the same colour. The first time I saw that I opened it in photoshop and cropped it to prove it to myself. ---
**Author:** ![TellMeI\_mNotCrazy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tellmei_mnotcrazy/32/3419_2.png) [@TellMeI\_mNotCrazy](https://boards.straightdope.com/u/TellMeI_mNotCrazy)\ **Post date:** [October 1, 2004, 3:19pm UTC](https://boards.straightdope.com/t/a-question-about-chewing-gum/267015/6 "2004-10-01T15:19:12Z")
I’m just going to point out for those unfamiliar, that \*\*Tir \*\* is referring to sidewalks when she says “pavements”. (Because to us Merkins, pavement and road are generally the same stuff) ---
**Author:** ![TellMeI\_mNotCrazy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tellmei_mnotcrazy/32/3419_2.png) [@TellMeI\_mNotCrazy](https://boards.straightdope.com/u/TellMeI_mNotCrazy)\ **Post date:** [October 1, 2004, 3:23pm UTC](https://boards.straightdope.com/t/a-question-about-chewing-gum/267015/7 "2004-10-01T15:23:29Z")
(and I meant to mention that the only reason _I_ mention it is because for about 2 minutes I sat here trying to work out the difference between “pavement” and “road” before finally remembering.) ---
**Author:** ![Otto](https://avatars.discourse-cdn.com/v4/letter/o/bbe5ce/32.png) [@Otto](https://boards.straightdope.com/u/Otto)\ **Post date:** [October 1, 2004, 3:28pm UTC](https://boards.straightdope.com/t/a-question-about-chewing-gum/267015/8 "2004-10-01T15:28:43Z")
Some of us dumb Americans got it right off… My WAG is that you’re noticing the color-contrasting gum because it stands out against its background. There’s probably plenty of dark gum on the asphalt and lots of light gum on the sidewalk, but it’s less obvious so you overlook it. Since people tend to remember the examples that support their theory and forget the ones that contradict it, you see a wad of light gum on the asphalt and say to yourself “see, the gum on the road is _always_ white” and vice versa for dark gum on the sidewalk. ---
**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:** [October 1, 2004, 3:31pm UTC](https://boards.straightdope.com/t/a-question-about-chewing-gum/267015/9 "2004-10-01T15:31:30Z")
I wonder if the gum dropped in pedestrian areas is more likely to get coated by cigarette ash, turning it dark. Actually, there’s probably a simpler explanation (not dissimilar to **pokey** ’s - gum that is dropped on the road and subsequently turns dark is essentially _invisible_, so maybe you’re only noticing the fresh stuff on the roads, but all of it on the pavement. ---
**Author:** ![Tir\_Tinuviel](https://avatars.discourse-cdn.com/v4/letter/t/bc79bd/32.png) [@Tir\_Tinuviel](https://boards.straightdope.com/u/Tir_Tinuviel)\ **Post date:** [October 1, 2004, 8:23pm UTC](https://boards.straightdope.com/t/a-question-about-chewing-gum/267015/10 "2004-10-01T20:23:09Z")
**pokey** and **Otto** , I know what you mean by the optical illusion, (I’ve seen some very cunning ones courtesy of **Ianzin** ) but honestly that is not happening here. I work with colours and shades as part of my job, and even with contrasting backgrounds, these are quite obviously not the same. I’ll get a piccy tomorrow or the next day (whenever I’m feel brave enough to venture out of the flat), that shows both the pavement(sidewalk) and the road. They are most definately different colours. The road is dark grey, this stuff is as white as the pure snow. The pavement is light grey and the gum is blacker than my heart. 😉 ---
**Author:** ![curly\_chick](https://avatars.discourse-cdn.com/v4/letter/c/7ba0ec/32.png) [@curly\_chick](https://boards.straightdope.com/u/curly_chick)\ **Post date:** [October 6, 2004, 10:12am UTC](https://boards.straightdope.com/t/a-question-about-chewing-gum/267015/11 "2004-10-06T10:12:47Z")
Howsabout this then, **Tir** a WAG from me - On the road, the gum is subjected to cars and buses going over the top of it. As the cars and buses and sundry other big traffic vehicles are exerting a huge downward force on the surface area of the gum, they peel of the top surface layer, exposing the fresh virgin white gum, taking it with them, where it can’t be seen, because a) It’s microscopically thin b) Tyres are all black anyway The dark gum on the pavement is only being trodden on by feet, and no person weighs as much as a car, so the downward pressure of someon’e foot is not enough to shear off the top layer. I suppose I ought to say that I am in no way a chewing gum scientist of international renown, but I reckon you already knew that. ---
**Author:** ![curly\_chick](https://avatars.discourse-cdn.com/v4/letter/c/7ba0ec/32.png) [@curly\_chick](https://boards.straightdope.com/u/curly_chick)\ **Post date:** [October 6, 2004, 10:17am UTC](https://boards.straightdope.com/t/a-question-about-chewing-gum/267015/12 "2004-10-06T10:17:38Z")
Sorry. I missed out a bit, which makes that post a bit confusing. The new bit’s in bold [QUOTE=curly chick] As the cars and buses and sundry other big traffic vehicles are exerting a huge downward force on the surface area of the gum, they peel of the top surface layer, exposing the fresh virgin white gum, \*\*taking the dirty top layer \*\* away with them, where it can’t be seen, because a) It’s microscopically thin b) Tyres are all black anyway [QUOTE] ---
**Author:** ![ZipperJJ](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zipperjj/32/211_2.png) [@ZipperJJ](https://boards.straightdope.com/u/ZipperJJ)\ **Post date:** [October 6, 2004, 3:55pm UTC](https://boards.straightdope.com/t/a-question-about-chewing-gum/267015/13 "2004-10-06T15:55:01Z")
Is it just that the gum on the asphalt has been driven over so much it’s been “polished” by all the tires, and therefore is reflecting all the light that hits it making it look white? **pokey** that illusion has blown my mind so far that I might not be able to work the rest of the day. woah. ---
**Author:** ![Tir\_Tinuviel](https://avatars.discourse-cdn.com/v4/letter/t/bc79bd/32.png) [@Tir\_Tinuviel](https://boards.straightdope.com/u/Tir_Tinuviel)\ **Post date:** [October 7, 2004, 2:40pm UTC](https://boards.straightdope.com/t/a-question-about-chewing-gum/267015/14 "2004-10-07T14:40:39Z")
I dunno **Curly** , would the chewing gum not have a stronger attachment to itself rather than a car tyre, especially if the top layer is covered in dirt it’ll no longer be sticky?