Relative dating principle
The second pair of subsamples was treated with a commercial detergent (1.5% SDS), distilled water, 0.1% HCL and another detergent (1.5% triton X-100); they were then submitted to a Soxhlet extraction with ethanol for 60 min and washed with distilled water at 70° C in an ultrasonic bath (method b).
The Oxford group divided the precleaned sample into three.
Following this intercomparison, a meeting was held in Turin in September-October 1986 at which seven radiocarbon laboratories (five AMS and two small gas-counter) recommended a protocol for dating the shroud. The samples were then taken to the adjacent Sala Capitolare where they were wrapped in aluminium foil and subsequently sealed inside numbered stainless-steel containers by the Archbishop of Turin and Dr Tite.
In October 1987, the offers from three AMS laboratories (Arizona, Oxford and Zurich) were selected by the Archbishop of Turin, Pontifical Custodian of the shroud, acting on instructions from the Holy See, owner of the shroud. Samples weighing 50 mg from two of the three controls were similarly packaged.
Gonella (Department of Physics, Turin Polytechnic and the Archbishop's scientific adviser), two textile experts (Professor F. Because the distinctive three-to-one herringbone twill weave of the shroud could not be matched in the controls, however, it was possible for a laboratory to identify the shroud sample.The Zurich group first split each ultrasonically cleaned sample in half, with the treatment of the second set of samples being deferred until the radiocarbon measurements on the first set had been completed.The first set of samples was further subdivided into three portions.One-third received no further treatment, one-third was submitted to a weak treatment with 0.5% HCL (room temperature), 0.25% Na OH (room temperature) and again in acid, with rinsing in between.