# Self cleaning oven ash **URL:** \ **Category:** Factual Questions\ **Created:** [May 5, 2018, 4:35pm UTC](https://boards.straightdope.com/t/self-cleaning-oven-ash/813646 "2018-05-05T16:35:14Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [May 5, 2018, 4:35pm UTC](https://boards.straightdope.com/t/self-cleaning-oven-ash/813646/1 "2018-05-05T16:35:14Z")
After I run the self cleaning cycle on my oven, the inside has patches covered with fine white ash, where debris has been incinerated. If I wipe up this ash with a damp paper towel, the paper towel is stained with BLACK ash. How does this magical color transformation happen? I have some theories but I want to hear other ideas. ---
**Author:** ![TimeWinder](https://avatars.discourse-cdn.com/v4/letter/t/bcef8e/32.png) [@TimeWinder](https://boards.straightdope.com/u/TimeWinder)\ **Post date:** [May 5, 2018, 4:49pm UTC](https://boards.straightdope.com/t/self-cleaning-oven-ash/813646/2 "2018-05-05T16:49:06Z")
My guess: The ash isn’t actually white, it’s grey. Looks white on dark oven, looks black on white paper towel (plus it’s now damp, which darkens any powder). Like those optical illusions you see all the time where the “dark square” in the light and the “light square” in shadow turn out to be the same color. (Second guess: There’s ash of both colors there, and you only see the one that contrasts on each surface.) ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [May 5, 2018, 6:56pm UTC](https://boards.straightdope.com/t/self-cleaning-oven-ash/813646/4 "2018-05-05T18:56:12Z")
reported ---
**Author:** ![ZurBob](https://avatars.discourse-cdn.com/v4/letter/z/71e660/32.png) [@ZurBob](https://boards.straightdope.com/u/ZurBob)\ **Post date:** [May 6, 2018, 12:00pm UTC](https://boards.straightdope.com/t/self-cleaning-oven-ash/813646/5 "2018-05-06T12:00:11Z")
Chemical reaction of the substance in the oven with the water in your towel due to a differing ph. ---
**Author:** ![Jeff\_Lichtman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jeff_lichtman/32/1531_2.png) [@Jeff\_Lichtman](https://boards.straightdope.com/u/Jeff_Lichtman)\ **Post date:** [May 7, 2018, 6:30pm UTC](https://boards.straightdope.com/t/self-cleaning-oven-ash/813646/6 "2018-05-07T18:30:21Z")
First, the ash isn’t pure white. It’s gray. This is the same phenomenon that causes rough surfaces to darken when they get wet. The ashes appear lighter when they’re dry because they scatter light randomly. Wetting the ashes reduces the scattering, so they appear darker. There’s a pretty good explanation [here](https://www.reddit.com/r/askscience/comments/37l9sk/why_do_things_look_darker_when_wet/). ---
**Author:** ![Melbourne](https://avatars.discourse-cdn.com/v4/letter/m/b5e925/32.png) [@Melbourne](https://boards.straightdope.com/u/Melbourne)\ **Post date:** [May 9, 2018, 10:02am UTC](https://boards.straightdope.com/t/self-cleaning-oven-ash/813646/7 "2018-05-09T10:02:40Z")
I’ve always noticed that the outside of ash is white, and the inside is black. That may be an effect of the surface structure, or it may be that the content is different. I don’t know. ---
**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\ **Post date:** [May 9, 2018, 10:37am UTC](https://boards.straightdope.com/t/self-cleaning-oven-ash/813646/8 "2018-05-09T10:37:01Z")
The moon looks pretty white, but on a white spacesuit the dust looks [pretty dark](http://sservi.nasa.gov/wp-content/uploads/2015/08/dustysuit.jpg).