According to
enth's write-up, the
carbon in the "bio-plastic
coating" would have to contain twice as much carbon as the
shroud
itself to change the shroud's
carbon dating date by 1300 years.
However, according to my calculations, this is almost right: it
coating would have to be about 1.83 times the mass of the shroud
itself (or, more specifically, for every pound of carbon in the
shroud, there would have to be 1.83 pounds of carbon in the coating).
(
NOTE: This is a lot more than the 0.14, or 14%, estimate
that I originally gave; my original calculations were wrong).
Here is my calculation: carbon-14 has a half life of 5730
years. Assume that the amount of carbon-14 in the atmosphere is
constant from century to century (which isn't exactly true), and
that 1 pound of carbon has 1 unit of carbon-14 in it. The shroud
was dated in 1988 to have an origin of 1350 A.D., a 638 year
difference; given this amount of time to decay, there would be
0.9257 units of C-14 per pound of carbon in the shroud.
If the shroud had been the burial shroud of Jesus, who died around
30 A.D., there would have been 1958 years for the C-14 to decay,
and there would be only 0.7899 units of C-14 per pound of carbon.
So, we need to add enough pounds of fresh carbon that the units
per pound of C-14 rises to 0.9257. As we add fresh carbon to the
shroud to increase the amount of C-14, we also increase the total
amount of carbon, and the units per pound measurement is the total
amount of C-14 divided by the total amount of carbon. Since
there's 1 unit of C-14 per pound of fresh carbon, we calculate how
many pounds of fresh carbon we'd have to add to a single pound of
shroud carbon to get the ratio right.
0.7899 + X <----- Total units of C-14
---------- = 0.9257 <----- Desired ration
1 + X <----- Total pounds of carbon
Solving for X, we get 1.83, so there'd have to be 1.83 pounds of
carbon in the coating for every pound of carbon in the shroud. In
other words, the shroud would have to be completely covered in
slime and dust, which would be rather obvious to the scientists.
Another theory I've seen is that the flax the linen was made
from fixes carbon-14 carbon-dioxide into chemicals more
readily than the normal kind of carbon. I find it extremely
unlikely that there's any kind of plant that fixes more carbon-14
than any other kind of plant, and if flax, a fairly important
plant, did this, I'm sure that the scientists who do carbon dating
would be aware of this and adjust for it.
A final theory that could be proposed, though I'm not sure if it
has been. There's some theories that the corpse of Christ
released radiation of the radioactive type while in the shroud,
which caused the image. If this did indeed happen, it could have
created a large amount of C-14 in the shroud, thus throwing the
carbon dating date some 1300 years into the future.