Perhaps some sort of batik, coating the other side with something resistant to the browning process?
There is no pigment on the Shroud... we know what the image is made of... and it is not pigment. It is the aged remnants of the soapwart fullering used to treat the original linen before it was woven into cloth, some of which has aged at a different rate then the rest. It is a for of sugar caramel that coats all of the fibers so thinly that its thickness is measured in nanometers. The chemistry is known... and it is not a pigment that is, or ever was used, or could be used in art.
We also know that the C14 dating done in 1988 was done on a portion of the Shroud that was a combination of original Shroud Linen material and patch Cotton material added at a later date using a 16th Century technique called French Invisible Reweaving that was used to repair tapestries that is all but literally "invisible" unless one knows what to look for. This has been proved by two independent studies of microphotographs of the tested samples and chemical tests of threads retained from the tested area which proved to chemically different from the main body of the Shroud. One of the threads retained came apart into two pieces, one side of which was original pure linen, the other one was cotton dyed to match the original linen and then spun and rewoven into the original cloth to repair a frayed area. The C14 test accurately dated a melange of original and 16th century fibers to come up with a spurious 12th to 14th century dating.
An unauthorized, unofficial C14 test was performed on another thread from a non-disputed portion of the Shroud and its result came back with a date of 1st Century plus or minus 100 years.