In 1978, a team of scientists was given direct access to the Shroud of Turin. It included specialists in imaging technology from NASA, and they arrived with equipment built for reading planetary surfaces from spacecraft data.

They expected to determine how the image had been made. They left with a deeper problem than the one they came to solve.

The first finding was negative, and decisive. There is no paint on the cloth. No pigment, no dye, no brushwork, no binding medium — none of the materials any artist in any century would have needed. Whatever formed the image, it was not applied to the linen.

Instead, the image consists of a chemical change in the fibres themselves — a discolouration of the cloth's own material, confined to the surface. The linen was altered rather than coated.

Then came the result nobody anticipated.

The team ran the image through a device designed to convert brightness values into elevation data — the technology used to build three-dimensional terrain maps from spacecraft imagery. Feed it an ordinary photograph and you get a distorted mess, because a photograph records light and shadow, not distance.

Feed it the Shroud and a coherent three-dimensional human form emerges. Face, body, proportions — correctly rendered in depth.

The image encodes distance. The intensity at every point on the cloth corresponds to how far the body was from the linen at that point.

No painting contains this information. No photograph contains this information. Artists work in two dimensions and record light; they have no means of encoding the distance from a surface to a body, and no reason to attempt it. The data is there in the Shroud regardless.

Study has also dated the cloth to the time of Christ, consistent with the historical record.

The 1978 examination is what moved the Shroud out of the category of religious relic and into the category of unsolved scientific problem. A team equipped with the most advanced imaging technology available established what the image is not — not paint, not scorch, not photograph — and uncovered a property in it that has no explanation at all.

Full-length negatives of the Shroud of Turin. Public domain, via Wikimedia Commons.