I suspect what appears to be 3D-ish elevation is a representation of relative chemical reaction completely unassociated with spatial relationships. 

imageHugh Farey in a comment to another posting writes:

Do we in fact know anything about the Volkringer patterns, except that they exist? Research into them seems vanishingly scarce, and there are only three purported examples on the internet, of which only one actually shows the plant and its effect. It’s a fern, which makes me think the pattern could be a spore print. One of the others is too badly reproduced to be sure whether it’s actually a print or the plant itself, and the other is the sort of image that might come from a VP-8, but without any context or explanation. John de Salvo’s paper on shroud.com (“The Image Formation Process of the Shroud of Turin and Its Similarities to Volckringer Patterns”) references a paper by Volckringer himself from 1942, but omits part of the title. He calls it: “Le probleme des empreintes devant la science,” but in fact it is called: “Le Saint-Suaire de Turin: Le problème des empreintes devant la science”, and is clearly more to do with the Shroud than it is to do with these patterns. Can anybody help?

imageThere is an informative comment by Marty Benton on this site from January 2012:

I wonder if what we think are 3D reliefs prepared from Volckringer patterns are not something altogether different. I suspect what appears to be 3D-ish elevation is a representation of relative chemical reaction completely unassociated with spatial relationships. 

The veins appear higher than the blade and higher still nearer to the center rib. That would seem to be where the most lactic acid would be transferred to the paper by contact and lakes of vapor. The leaf seems really fat with an unnaturally beveled edge. That apparent bevel may result from less lactic acid reaching the paper at the edge of the leaf.

To fully assess this we need to see the facing pages from the book that held the leaf. Ideally, we need to see the leaf.  We need to know which side of the leaf is being plotted for 3D content. I imagine the facing page’s imprint might have a similar appearance of elevated veins and a fat bevel. That would not make sense.

The point is that because something appears to have 3D characteristics, it may not be a real spatial representation. I’m not saying the Shroud’s image isn’t spatial data, what you call a height-field. I’m saying, however, that we must consider other possibilities.

More Information:

The DeSalvo paper Hugh mentions can be found HERE (shroud.com) and HERE (Penn State).

There is also a presentation by John DeSalvo, Shroud of Turin Picture with a brief description on page 3:

I decided to explore this similarity in more detail.  I was hoping that by understanding how Volckringer Patterns are produced, it would give me some idea of how the Shroud body image was produced.  Using a spectrophotometer I did a color comparison between the Volckringer patterns and the Shroud body image.  Within experimental error, I showed that the Volckringer patterns were identical in color to the Shroud body image.  I than compared the Shroud and Volckringer patterns using UV Fluorescent studies.  It was shown that both the Volckringer patterns and the Shroud body image do not fluoresce under UV light.  Thus the Volckringer patterns and Shroud body image also have identical UV fluorescent characteristics.

The most startling similarity was that the Volckringer patterns could be reconstructed in 3D relief using a VP-8 analyzer, just like the Shroud body image.

There is a brief write up in Mark Antonacci’s The Resurrection of the Shroud (pages 68 and 69 readable online at Google Books)

In I 942, Dr. Jean Volkringer, a pharmacist at St. Joseph’s Hospital in Paris, discovered that when certain plants arc pressed between the pages of a hook, a highly detailed negative image appears on adjacent pages. He proposed this discovery as a possible explanation of what is seen on the Turin Shroud. However, such a mechanism cannot explain the Shroud image. in the first place, plants that produced such images were usually pressed in books for several decades, some for as long as a century. …