that unforgivable hoovering
Colin Berry, with his non-stop observant and inquisitive mind:
Am I not correct in thinking that there are dark specks associated with the tan-coloured areas, which are unlikely to be artefactual (chance deposits of dust etc) given they are absent for all intents and purposes in the less-strongly coloured non-image areas?
Flour particles, toasted?
(click on picture to see enlarged version)
A working hypothesis:
Working hypothesis. There are (or were, before the 2002 conservation measures, including that unforgivable hoovering) a scattering of dark-coloured particles on the TS concentrated mainly in the image-bearing regions, with far fewer in non-image regions.
An analysis of those particles would show them to be a substance that has been rendered yellow or brown by thermal energy ("heat" in common parlance). A possible candidate might be white flour particles – an intentional additive – one that acquired colour via a Maillard reaction, thus contributing to the image-forming process and hence its heterogeneity and complexity.
Do they match what we see in the Mark Evans pictures?
As ever, more and more work beckons. First, one will need to do microscopy on the flour-coated imprinted linen to see what happens to the appearance of individual flour particles, and whether or not they match the specks one sees in the above Mark Evans pictures, at least in terms of size.
And what did McCrone see?
Then comes the difficult part: to track down such papers are available online from the Walter McCrone Microscopy Institute on the studies he did on sticky-tape samples supplied by Ray Rogers. I definitely recall seeing one summary that had a long long list of the different types of particle he had identified.
One wonders what he would have made of those dark specks we see above if indeed they were flour or some other ‘food’ type particle that had undergone a Maillard reaction. One imagines it would take some fairly sophisticated kind of spectrographic microscopy to make a positive identification, but that is not my area, so there’s a steep learning curve that will need to be climbed to make headway.