Beware the mirage of apparent reverse-side scorching produced by the ‘BROIL’ effect.

This is essentially a repeat of yesterday’s posting, using a scorch image (off a crucifix) instead of that red marker pen.

I’ll let the pictures speak largely for themselves.

BROIL = Back Radiation Of Incomplete Light.

(OK, so filtered light, coloured due to  certain missing wavelengths, has to be described somewhat unconventionally as “incomplete”.  But there’s such a thing as acronymic licence, surely? Come on, say yes.)

In this instance the light passing through the scorch has emerged as yellow/brown, due to abstraction of its short-wave blue component by the pyrolysed carbohydrates. When linen is placed down on a white surface, most of that yellow light gets reflected/radiated back through the interstices to the viewer’s eye, creating a mirage of a heavier scorch on the reverse side than is really the case. Viewing the reverse side on a black surface allows one to compare the real v mirage-reinforced reverse-side image.

DSC09749(Ignore the writing – it was a reference to there being a damp backing cloth in the original scorch experiment. The cloth used today was bone dry.)

First, this shows how white light being transmitted through a scorch image is filtered. The filtered light, now yellow/brown as per scorch, creates a patch on the white background. Note the presence of a gap between fabric and paper. But when the linen is then placed back on the white paper, that yellow light then gets reflected back through the interstices of the weave.



It’s the back-radiation of filtered/coloured  light that accounts for the anomaly you see in the above photo, where the colour of a reverse-side image appears to be mainly in the interstices of the weave, when viewing on a white background. Once could almost imagine that it was yellow or brown paper behind the fabric.

The moral is clear: if you think there is reverse-side scorching, especially from a faint top-side scorch, then always view against a matt black surface. Don’t be fooled by the BROIL- mirage. (Mirages, in the desert etc, are caused by refraction of light. This one’s caused by back-reflection/scattering, but it’s a similar idea of light playing tricks).

Caveat: it was necessary to choose a heavy front-side scorch from my collection in order to capture that transmitted yellow light on the backing white paper. Consequently there WAS some real reverse-side image that is not seen on lighter front-side scorches. Nevertheless, a sizeable difference in reverse side intensity was seen when comparing white  (left) v black (right) background. Sorry, the images are not quite the same size for the purposes of strict comparability, but  I maintain that occasional sloppiness and indolence  is an essential prerequisite for staying power in science.





Once again, I’m giving Google no help in putting my ideas and images onto targeted searches under (shroud turin + additional term ), not while this site with its 202 postings languishes out of sight on Page 12 or 13 of  (shroud of turin) returns, with priority being given to so many 9-day wonder stories.  In fact, thanks to Google, stories that should be 9-day wonders hang around in top listings for 90 or even 190 days!   Fix that algorithm, Google, or pay someone to manually mark up the sites that offer real content and long-term commitment, and mark down the flash-in-pan content. Don’t do evil. Don’t even do lazy robotic dysfunctional.


About Colin Berry

Retired science bod, previous research interests: phototherapy of neonatal jaundice, membrane influences on microsomal UDP-glucuronyltransferase, defective bilirubin and xenobiotic conjugation and hepatic excretion, dietary fibre and resistant starch.
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