John P. Jackson:
"Heated Bas-Relief/Scorch Theory Another possible image-forming mechanism similar to that proposed by Nickell involves pressing a stretched cloth over a heated bas-relief. Such an idea was first proposed in 1961 and tested, with limited success, by placing a white handkerchief on top of a heated small medallion that bore a carving of a horse. This theory is more intriguing than most because the Shroud image does appear to have many of the physical and chemical properties of a light scorch. STURP scientists Jackson, Jumper, and Ercoline tried to duplicate the image on the Shroud by testing the scorch hypothesis more fully. To accomplish this, they heated a full-size bas-relief model of a face and stretched over it a linen cloth of a thickness similar to the Shroud. The ... resulting image lacks the high resolution and sharp focus found on the Shroud.
“While the bas-relief method seemingly yields a respectable three-dimensional image, problems are evident in the accompanying VP-8 relief of this image.
"Even though the heated bas-relief produced better three-dimensional information than other methods, Jackson and colleagues concluded that this process could not encode many of the necessary Shroud image characteristics. For example, regardless of the temperature of the bas-relief, thermal discoloration appeared on the back side of the test cloth within several seconds after being placed on the hot bas-relief. Thus, the superficiality characteristic is violated because the image could not be encoded only on the topmost fibrils of the linen."
“The researchers tried to circumvent this problem by wetting the cloth, thereby extending the scorch time. When this technique was tried, new problems appeared. The image's contrast was reduced, causing more severe distortions in the three-dimensional analysis and resembling images obtained from direct-contact techniques ... In addition, because the cloth was essentially flat when the image was encoded, tests of this image-forming method failed to generate an image that contains the subtle lateral distortions that are consistent with the cloth-drape effects found on the Shroud."