Photography of the shroud by Secondo Pia in 1898 indicated that the image resembled a photographic 'negative' and represents the first modern study.
Each subsample was treated with 1M HCL (80° C for 2h), 1M Na OH (80° C for 2 h) and again in acid, with rinsing in between.
Two of the three samples were then bleached in Na OCL (2.5% at p H-3 for 30 min).
At the same time, the British Museum was invited to help in the certification of the samples provided and in the statistical analysis of the results. The age of the shroud is obtained as AD 1260-1390, with at least 95% confidence. The three containers containing the shroud (to be referred to as sample 1) and two control samples (samples 2 and 3) were then handed to representatives of each of the three laboratories together with a sample of the third control (sample 4), which was in the form of threads.
The procedures for taking the samples and treating the results were discussed by representatives of the three chosen laboratories at a meeting at the British Museum in January 1988 and their recommendations = standard deviation) errors, of the Shroud of Turin and control samples, as supplied by the three laboratories (A, Arizona; O, Oxford; Z, Zurich) (See also Table 2.) The shroud is sample 1, and the three controls are samples 2-4. The sampling of the shroud took place in the Sacristy at Turin Cathedral on the morning of 21 April 1988. All these operations, except for the wrapping of the samples in foil and their placing in containers, were fully documented by video film and photography.
Zurich precleaned the sample in an ultrasonic bath.