THE FABRIC OF THE SHROUD
Flax is a herbaceous plant with blue flowers. It is cultivated for its seeds from which linseed oil is extracted, and for its stems from which the fibres are extracted and spun to produce thread which is often woven to produce linen cloth.
Once the stems have been collected, they are soaked in water-filled ponds until the fibres
separate from each other as the substance that glued them together dissolves. In British
English this operation is called "Retting". Once done, the stems are dried, then
crushed to liberate the fibres which are combed out to give them the same direction, and
spun into yarn on a distaff / spindle : i.e. constantly and regularly pulling out a number
of overlapping fibres and twisting them together to make a continuous thread. Flax is
normally twisted to give what is called an "S" twist which follows the
spontaneous torsion of Flaxen threads as they dry. In the case of the thread used for the
Shroud, the torsion was the reverse of this, so that the aspect of the thread is a Z
shape. Apparently this "Z shaped" spinning was somewhat rare because the flax
has to be spun simultaneously with both hands. On the photo below, we can see the fibres
in the threads and we see clearly their oblique position from upper right to lower left,
which is characteristic of the letter Z. After spinning, the thread was bleached, probably
by immersion in a reducing bath.
On the Shroud, we see about 38 threads per centimetre for the warp, and about 26 for the weft. We say about, because spinning was performed by hand, and the diameter of the thread varied with variations in the natural fibres, and with the skill of the spinner. At 38 threads per cm., the average diameter of each thread is about 0.26 mm. The variation in diameter of the threads is quite visible in the photo.
Before starting to weave, the weaver first had to tie the linen threads along an upper or forward horizontal bar on the loom. This setting up of parallel vertical threads made the warp. The threads were kept taut by a number of hanging weights. As far as the Shroud was concerned, depending on whether you think that the lateral band was part of the original cloth or not, a problem that has not been definitely settled, it seems that the total width was 1.0 metre or 1.08 metres, which means about 4,000 parallel threads in the warp. After that, the weaving consists in passing a linen thread horizontally (the weft in British English, known as the filling in American English) between the threads of the warp.
The Turin Shroud is made of linen threads woven in a herringbone pattern of 3 under 1, i.e, each weft thread passes under three warp threads and then over one, under three and over one, etc. With each successive thread, the pattern is staggered by one thread. This happens 40 times in succession (11 cms) to give the weave its oblique aspect. Then there is a change of direction, which give the cloth its chevron or herringbone pattern. The total weight of the Shroud is 1.12 kg, and its average thickness is 0.3 mm, giving an average weight of 20 milligrammes per square centimetre.
The fact that there is one thread above and three threads underneath, gives a different aspect to the two sides of the cloth. On one side, the warp threads predominate, and this is called the "front". On the other, the weft thread predominates, and this is called the "reverse". Fortunately, on the Shroud, it is the "front" that received the image, for this side gives clearer details.
Monsieur Gabriel VIAL gave an extremely detailed paper at the Paris Symposium of 1989, in which he explains that there had to be 4 blades over which the threads passed in order to get this herringbone effect. Out of 4000 warp threads, errors in the passage of threads were unavoidable, and these errors obviously happened all along the fabric. They were studied, by Mr VIAL, (see in the bibliography CIELT, Actes du Symposium, Le Prélèvement, Etude du tissu).
What is the thread composed of ?
Each thread is composed of about 70 fibres (average diameter 15 micron, average length 22mm) twisted together during spinning, and each fibre, which appears under the microscope as a sort of flattened and twisted pipe, is composed of long chains of cellulose.
The cellulose is a polymer of beta gluco pyrannose molecules, a compound formed by the fusion of two molecules of glucose (a well known sugar) with the formula C6H12O6.
These molecules of glucose are linked through the Carbon 1 and 4 atoms with the loss of a molecule of water. The formula of cellulose could be written (C6 H10 O5)n
When you polymerise several thousand molecules of glucose in a long
chain, you get a fragment of a fibre of cellulose. These long chain macro-molecules then
bond side by side to each other, under the effect of hydrogen bonding and Van der Waals
forces, to produce super-macro-molecules. Assemblies of these give a flax fibre, and flax
fibres when spun together make a thread.
And what about colour in all this? When the cellulose starts
dehydrating, losing its water molecules, the ring compounds in the basic molecules alter.
Alpha-beta unsaturates, and alpha-dicarbonyl groups, which form in the side chains to the
rings, absorb different radiations, and reflect different radiations (including radiations
in the visible spectrum), to the normal molecules. Where this happens the fibres turn
yellow, and it is exactly because the cellulose in the flax fibres underwent this
oxidation / dehydration, that some fibres of the Shroud turned yellow in places. (Details
from Maurizio Bettinnelli at the "Symposium de Rome" in 1993).
We have to say that nobody knows exactly when the image appeared on the Shroud. Was it immediately, or after several hours, or did it develop after the body was gone, i.e. days, or months, or years later? Its delayed appearance could explain the fact that the Gospels do not mention its existence, (although we know that any animal or human representation was strictly forbidden in Jerusalem, which would have discouraged people from talking about it). The question can be considered alongside the fact that the whole Shroud seems to be yellowing further with time, as if all its surface were subject to this slow oxidation process. Some experts are thinking seriously about this, and the question of preservation.