Three Innovative Dating Methods
The search for new and reliable methods of dating minute fragments of linen fabric was one of the research objectives of a team of Italian scientists led by Professor Giulio Fanti of Padua University. This research was ultimately extremely successful and led to the discovery of three new ways in which it was possible to measure the age of linen by analysing the amount of age-related cellulose degradation. Unlike radiocarbon dating, these three methods outlined below – Fourier Transform Infrared Spectroscopy, Raman Spectroscopy and Mechanical Measurements of strength and elasticity – were all non-destructive and so did not destroy the samples used for testing.
Evaluation Process
The following process was adopted for calibrating and evaluating all three of these potential dating methods:
- A selection of flax samples taken from various new and ancient linen artefacts of known age was used to confirm a reliable relationship between the measurements made and the age of the samples tested.
- Once they had established a formula that could be used to calculate the age of a sample from its measurement, the formula was validated using a statistical test known as Pearson’s Correlation Coefficient. This test provides a measure of the accuracy on a scale of -1 to +1, where +1 means that the calculation produces results which perfectly match the test data. A value above 0.7 is usually regarded as evidence of a strong correlation between a formula and its related measurements.
- They then ran tests to check what effect, if any, the conditions of the 1532 Chambery fire could have had on the measurements. To do this, they took samples of new linen of similar quality to the Shroud and heated them in an oven, causing the material to discolour until it matched the background colour of the Shroud. They could then compare the measurements made before and after heating the fabric and, if necessary, make adjustments to the calculations to compensate for the effect of the Chambery fire until the colour of the material
- After completing the above, they were then ready to use each of these methods to date linen samples that originated from the Shroud.
Fourier Transform Infrared Spectroscopy (FT-IR)
FT-IR analyses materials by exposing them to a range of infrared frequencies and measuring the absorption made by various molecular bonds. When the radiation frequency corresponds with the resonant frequency of a molecular bond, some of the radiation at that frequency is absorbed which produces a dip at that point in the spectrum.
When Giulio Fanti and his colleagues used FT-IR to test the selection of flax samples, they found that the spectrum intensity in certain frequency ranges was age-dependent with an exponential decay curve. They eventually found two different ratios of aggregate intensity measurements over specific frequency ranges which correlated with the sample age. From this they were able to derive two equations which showed a close alignment between the calculated dates for each of the eight samples and their known date.
They validated these equations using the Pearson’s Correlation Coefficient test, which gave 0.899 and 0.949 and provided an excellent endorsement of the accuracy of these equations. They also calculated the measurement uncertainty to be plus or minus 400 years for a 95% confidence in the result.
The Shroud sample was then tested using FT-IR and the two equations gave results of 200 BC and 297BC respectively, with a mean value of approximately 250 BC plus or minus 400 years at a 95% confidence level. This result indicates that the fabric of the Shroud is much older than the result of the radiocarbon test and is compatible with claims that it originated in the first century.
Raman Spectroscopy
In Raman Spectroscopy, samples are exposed to a single frequency laser beam, with a frequency in the range between ultraviolet and infrared. This produces a spectrum with peaks that indicate the sample’s chemical composition. When photons of light from the laser source strike molecular bonds present in the sample, they cause an increase in the rate of vibration. Both visible light and ultraviolet radiation have a higher frequency than infrared radiation and so these photons carry significantly more energy, enough to cause the vibrational frequency of a bond to surge above its natural energy states to a virtual energy level. The bond immediately returns to one of its natural vibrational energy states, emitting a photon in the process with a frequency that corresponds to the drop in energy.
The Shroud sample was then tested using Raman spectroscopy which produced a result of 200 BC plus or minus 500 years at a 95% confidence level. This is a similar outcome to the FT-IR result and is once again compatible with a first century origin for the fabric of the Shroud.
Each molecule has its own Raman spectrum, which is a kind of ‘fingerprint’ that can be used to identify the chemical composition of a sample of material. However, the team discovered that the intensity of peaks in the Raman spectrum produced by linen is also affected by age-related cellulose degradation.
When Giulio Fanti and his team tested the selection of flax samples using Raman spectroscopy, they found that these samples produced varying amounts of background fluorescence which affected the relationship between sample age and the ratio of the intensity measurements. These were categorised as either low or high fluorescence based upon the level of background intensity and two separate equations were produced, one for use when calculating the age of high fluorescence samples and one for use with low fluorescence samples. The accuracy of these two equations was evaluated using Pearson’s correlation coefficient test, which gave excellent values of 0.947 and 0.907 for the high and low fluorescence equations respectively.
Fibre Strength and Elasticity
Age-related degradation of cellulose also affects the physical attributes of the flax fibres that are used to make linen. The long cellulose molecular chains slowly fragment into smaller pieces over time, causing the cellulose structure to become less crystalline and increasingly amorphous. This results in changes to some of the fibre’s mechanical characteristics, such as its strength and elasticity.
Initial tests conducted by Giulio Fanti’s team found that fibres from newer samples could withstand higher loads than those from older fabrics, which indicated that there was a link between sample age and the breaking load. However, in order to measure the minute stresses and strains acting upon flax fibres under tension, it was necessary to design and custom-build a highly sensitive instrument called a Microcycling Tensile Machine that could measure forces to a resolution of 2 micronewtons and elongation to a resolution of 0.1 micrometres. For comparison, the diameter of a typical human hair is about 70 micrometres and a thread of silk from a spider web is about 3 micrometres, thirty times the resolution of this equipment!
© Giulio Fanti
They used this equipment to measure various mechanical properties of the flax fibres taken from the selection of linen samples to assess whether this mechanical method could be used to measure the age of flax fibres. They discovered five different mechanical properties which showed a clear correlation with the age of each sample. Each of the five equations which they derived for calculating the age produced a Pearson’s Calculation Coefficient value above 0.9, indicating that the equations were very accurate.
They then used each of these calculations to determine the age of fibres taken from an area of the Shroud that corresponded with the pelvis. The results obtained from the five equations were combined to give consolidated dating result of 400 AD plus or minus 400 years at a 95% confidence level. Once again, this result was compatible with a first century origin for the Shroud and much older than the result of the radiocarbon dating test.
Summary of Dating Results
The Table below summarises the results of these three separate dating tests of material from the Shroud.
| DATING METHOD | SHROUD DATING RESULT |
| FT-IR | 250 BC ± 400 years |
| Raman Spectroscopy | 200 BC ± 500 years |
| Fibre Strength and Elasticity | 400 AD ± 400 years |
| MEAN DATE | 33 BC ± 250 years |
Mechanical Test Refinements
Despite the positive outcome of the Mechanical Dating research, it was clear that there was room for some improvements to both the equipment and the process. For example, the method of mounting fibres was problematic, causing approximately 30% of the fibres to break before any tension had been applied. To help address this problem, the machine was fitted with an improved fibre clamping system and the components used to measure the applied force and fibre displacements were also enhanced.
This new approach changed the relationship that had previously been calculated between some of the properties and the sample age, making it necessary to recalibrate and validate those equations before they could be used. However, the existing breaking load formula proved to be even more reliable using the new system and so this property was measured for a fibres taken from the wrist area of the Shroud. This calculated the date of the Shroud to be 110 AD ±400 years with a 95% confidence level, a result which was in a similar range to that obtained in previous mechanical tests and once again compatible with a first century origin.
The following links provide further information on this research
Non-destructive dating of ancient flax textiles by means of vibrational spectroscopy. Research paper by Giulio Fanti, Pietro Baraldi, Roberto Basso and Anna Tinti published in Vibrational Spectroscopy Vol. 67 (2013) pp 61–70
Mechanical and opto-chemical dating of the Turin Shroud. Research paper by Giulio Fanti, Pierandrea Malfi and Fabio Crosilla published by MATEC Web of Conferences, Vol. 36, Article 01001 (2015)
