# Gasoline Sheen on Roast Beef?

**URL:** <https://boards.straightdope.com/t/gasoline-sheen-on-roast-beef/143784>\
**Category:** Factual Questions\
**Created:** [December 19, 2002, 1:20pm UTC](https://boards.straightdope.com/t/gasoline-sheen-on-roast-beef/143784 "2002-12-19T13:20:13Z")\
**Posts on this page:** 1\
**Showing post:** 5

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**Author:** ![Popup](https://avatars.discourse-cdn.com/v4/letter/p/94ad74/32.png) [@Popup](https://boards.straightdope.com/u/Popup)\
**Post date:** [December 19, 2002, 2:33pm UTC](https://boards.straightdope.com/t/gasoline-sheen-on-roast-beef/143784/5 "2002-12-19T14:33:24Z")

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Yup, I believe that **Mangetout** is on the right track. **Alton Brown** claims that it’s birefringence, and I’m bound to agree:

> [@](#):
>
> Speaking of color, you ever notice the rainbow effect that sometimes appears on the surface of freshly cut tuna? It’s not from age and it’s not fat. It’s birefringence.  
> [reading from a book] "\*Anisotropism of the refractive index which varies as a function of polarization and fre … "

(from [here](http://www.goodeatsfanpage.com/Season6/TunaTranscript.htm))

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