This is a holding post. I’ll add the details later. For now, it’s a case of one picture being worth a thousand words.
IMPORTANT: NOW UPDATED WITH NEW INFORMATION ON TEMPERATURES (SEE AT END OF ORIGINAL POSTING)
Actually, what this experiment shows is that a more intense image is obtained on the impregnated linen than the control, untreated linen, for heated metal templates at the same temperature. You will have to take my word for now that images can be obtained at lower temperatures on the impregnated linen with scarcely if any image on untreated linen.
It may well be that none of the imaging on treated linen is due to modification of linen carbohydrates, whether the cellulose or even the more heat-sensitive hemicelluloses etc of the primary cell wall. It may be that ALL the image represents pyrolysed products in the lemon juice. In other words, one can have thermal imprinting using a heat-sensitive invisible “ink” that need not damage or affect the linen itself. This makes it more probable that the image thickness meets that 2o0nm criterion!
A recent paper (pdf) reports that lemon juice can produce a brown coloration on glass as well as linen, i.e. that no chemical reaction with linen constituents is needed to explain the “invisible writing” effect.
Incidentally: this result was predicted in a comment I made in reply to Matthias this morning in regard to fluorescence. It’s always good to have one’s predictions confirmed. It gives one confidence that one is doing something right. (Important, given the number of mean-spirited detractors out there who think nothing of demeaning one’s scientific competence and/or credentials).
Other news: I have responded to Thibault Heimburger regarding the macroscopic aspects of his scorching experiments. Microscopic aspects will be the subject of a second instalment, probably tomorrow, the writing of which will be aided by today’s result.
Kelly Kearse has confirmed my hunch that Alan D.Adler did NOT have hard data to back up his claim for an “extraordinary” amount of bilirubin in the Shroud’s bloodstains. One is now entitled to ask whether he even detected ANY bilirubin by anything other than a spot test, far less quantify it.. I shall say more about this entire bilirubin fiasco – A LOT MORE – in due course.
Apologies for the terseness of this post. I have had to write this in a hurry, and will be away from my laptop for most of the day.
Afterthought: I have now come full circle. My very first posting (Dec 30 2011 on my sciencebuzz site) described the use of a thermosensitizer (charcoal) to make possible scorching-by-infrared radiation at a distance (sizeable air gap). But I dropped that radiation model when I realized (or rather had it pointed out to me) that the image was not a Shroud-like pseudo-negative. That was my reason for dropping radiation, and looking at scorching by direct contact/heat conduction instead. And now I have a thermosensitizer for the conduction model – plain old lemon juice. I shall naturally be testing some other well-known invisible ink recipes, e.g. sodium carbonate.
UPDATE: SATURDAY 27 OCTOBER
Here’s more evidence that the temperature for producing a visible scorch is considerably reduced using linen that has been impregnated with lemon juice. Previously I had to set my fan oven to its highest setting (250 degrees C) to get barely visible scorching with a heated template pressed onto untreated linen. Here, there is visible scorching at 190 degrees C, well below the reported pyrolysis temperature (220 degrees) of even the most sensitive linen constituents, ie. the hemicelluloses.
It seems highly probable that what we see here is purely an ‘invisible ink’ effect, i.e. due to colour changes in the heated lemon residue per se, given that lemon juice converts to a dark brown glassy residue when in contact with glass only, i.e. no linen:
(One might think that the above “burnt on” residue would have been difficult to shift, though not so (according to the missus). So I got to wondering whether the ‘burnt lemon juice’ pigment would wash easily out of the linen. Answer: no, despite kneading in cold water quite vigorously. At the moment I have to keep an open mind as to whether or not the linen carbohydrates have been modified, or whether there is merely a strong physical association between ‘burnt lemon’ and otherwise pristine linen. From a modelling point of view, a strong association between ‘thermosensitizer’ and linen is preferable, given the evidence that water stains have failed to elute body image from the Shroud’s fabric, i.e. transport from their original location with the moving solvent front, indicative of weak pigment-linen interaction.)
We now have to consider the interesting possibility that a medieval forger, cognizant of the ‘invisible ink’ effect, might have impregnated some linen with citrus fruit juice (or maybe some other acid/sugar combination) and been able to thermally imprint an image from a suitable template (metal? ceramic? plaster of Paris?) at a much lower temperature than that required using untreated linen. Is the Shroud image really modified linen carbohydrate or a coating that has become caramelised? Shades of Raymond N.Rogers, and his ‘impurity coating hypothesis’ but my model still incorporates the template/scorch model to account for that highly superficial negative image, concentrated mainly on the most superficial parts of the weave which rival models struggle to explain (Rogers with his migrating sugars) or which simply ignore (all the radiation models) ….
Wiki entry on lemon:
Lemons entered Europe near southern Italy no later than the 1st century AD, during the time of Ancient Rome. However, they were not widely cultivated. They were later introduced to Persia and then to Iraq and Egypt around 700 AD. The lemon was first recorded in literature in a 10th century Arabic treatise on farming, and was also used as an ornamental plant in early Islamic gardens. It was distributed widely throughout the Arab world and the Mediterranean region between 1000 and 1150.
The first substantial cultivation of lemons in Europe began in Genoa in the middle of the 15th century.
So, lemons would have had a great novelty value in the Arab and Mediterranean world in the medieval era. At some point, invisible writing with lemon juice would have been discovered by accident. Did that put the idea into someone’s head to create a unique artefact? Was that someone successful beyond his wildest dreams?
Templar, Holy Land connection? Even the Vatican( or at any rate, Vatican researcher) is now suggesting that the Shroud was in the care of Templars, they who helped finance the last Crusades, prior to its first showing by the knightly De Charny family in Lirey approx 1355.
Update: September 28, 2014
It’s almost two years since I reported this experiment, which went down like the proverbial lead balloon when news of it reached a certain pro-authenticity shroudie site. To say the reception was derisive would be an understatement, but that was not the chief reason this experimentalist dropped the ‘lemon juice’ model, about which more later.
For now, let’s leave it at saying that all the current revisiting of old, allegedly discarded ideas re the TS image having been ‘painted-on’ made me re-think the possibilities of painting-on an image with a stiff paste of lemon-juice (or something chemically similar) and then heating to produce/develop the ‘invisible ink’ effect.
The first thing to do was confirm my previous finding, with better photographic recording of the outcome, which I have just this minute done (successfully I’m relieved to say).
As before: serial scorch imprints from a heated metal template, going hottest (left) to coolest (right) as the template lost heat to the linen.
Top half: linen impregnated with lemon juice, then air-dried. Lower half: water-soaked control, air dried. Both then overlapped and imprinted simultaneously with a heated metal template.
The black regions are added to provide a background against which it’s easier to see the linen.
Note that the lemon-juice impregnated top half could be scorched by the cooling template at a temperature (undetermined) that scarcely affected the water control. The scorched experimental (top half ) was then bisected with scissors to see if the scorch pigment could be dissolved out with water. The little notches were removed with scissors to keep track of which was which (water v dry control).
Here one can see that the scorch that was dependent on prior lemon-juice impregnation does NOT dissolve out with water. That suggests, does it not, that the linen fibres have been permanently and irreversibly etched by something in the lemon juice, at a temperature below that which scorches untreated linen?
So what are the key ingredients in lemon juice that sensitize linen to scorching?
Note added 30 Sep 2014: have had to delete all the following, having just discovered that one must NOT overlap two test fabrics. They must be edge-butted. Overlapping produces an excessively-intense scorch on the top layer? Why? Because in all my experiments I have routinely been using a damp underlay to prevent excessive scorching. If one introduces an extra layer of linen, as one does when overlapping, the protection from the damp underlay is largely lost, and one gets misleading results that make particular impregnating agents look better or worse than they really are, depending on which has the additional underlay protection. I’m glad I spotted this source of error sooner rather than later.
All these experiments will now be repeated with butted edges, and the results will be reported on my sciencebuzz site.
Preliminary findings: ability of lemon-juice to sensitize linen to ‘scorching’ off a heated template CANNOT be reproduced with citric acid and sugar(s), singly or in combination. Something else in the lemon juice is responsible, and it may be that it is a substance that becomes yellow or brown when exposed to heat, i.e. that the enhanced scorch is not entirely on the linen, but an imported chromophore. It may be necessary to change nomenclature, e.g. to refer to lemon-juice ‘tanning’ of linen.
Sugar(s): here’s a comparison between glucose-impregnated cloth v water control, both after air-drying and scorching: Glucose (lower half): glucose impregnation permitted scorching at lower temperatures. Here’s a closer view of the right hand side, where the fainter scorches show the difference more clearly than the more intense ones: Upper half: H2O control, lower half: glucose impregnated. In situ caramelisation(?) of solid microcrystalline glucose results in a more intense scorch than that possible with untreated linen. The test was then repeated, but this time comparing glucose (upper half) with a mixture of glucose and citric acid (lower half): It would appear that that the citric acid of lemon juice is not the agent that is responsible for increased sensitivity to scorching. It is glucose and/or other sugars, the latter still to be tested. Mechanism? Possibly (a) caramelization of the sugar or (b) less probably, a Maillard reaction between the reducing sugar and traces of protein.
Sep 30, 2014: see my new posting on the invisible ink effect.