As part of my on/off efforts to produce a definitive list of information about the shroud I re-read the original documentation of the radiocarbon examination process. This leads me to consider the idea of sample contamination (beloved of the shroudies) is even less likely than I'd previously considered.
Each laboratory (Zürich, Oxford and Arizona) carried out a comprehensive, multi-stage, cleaning of their sample. Firstly by microscopic examination and removal of gross contaminants, followed by preliminary cleaning using a mix of ultrasonic bathing, vacuum pipetting and/or hot ether soaking.
After this the samples were split and more stringent methods were used.
Zürich
The Zürich group split each ultrasonically cleansed sample in half; the first half of the original sample was again split into three parts and these [one sixth portions] were subjected to different tratments:
1. soaking in room temperature baths of 0.5% hydrochloric acid, 0.25% sodium hydroxide and then acid again; samples were rinsed with purified water between each course.
2. no further treatment
3. soaking in hot (80°C) 5% hydrochloric acid, 2.5% sodium hydroxide and then acid again; samples were rinsed with purified water between each course.
The second batch of samples were retained until after the first radiocarbon dating run was completed. As this showed no evidence of contamination, the second set was split into two portions, to which the weak and strong chemical treatments were applied.
Arizona
The Arizona group split the shroud sample into four subsamples.
1. one pair of subsamples was treated by soaking in dilute hydrochloric acid, dilute sodium hydroxide and again acid, with purified water rinsing in between baths.
2. the second pair of subsamples was treated with two commercial detergents (with advice supplied by Proctor & Gamble), distilled water and 0.1% hydrochloric acid; after this the samples were then submitted to a Soxhlet extraction with ethanol for an hour, followed by further washing with distilled water at 70°C in an ultrasonic bath.
Oxford
The Oxford group divided their pre-cleaned sample into three parts.
1. all three parts were bathed in 1 molar hydrochloric acid at 80°C for two hours followed by 1 molar sodium hydroxide at 80°C for two hours and again in acid, with rinsing in between.
2. two of the three samples were then bleached in 2.5% sodium oxychloride [bleach] for thirty minutes.
Each laboratory used the same techniques on the four cloth samples provided, the shroud and the three controls with one exception; one of the control samples used at Zürich disintegrated while being cleaned and so it was additionally centrifuged to retain the material.