The “TAD” Carving in Raking Light (RTI)

Reflectance transformation imaging (RTI) is a technique museums use to study carvings and inscriptions. The camera stays fixed on a tripod while a light is moved to a different low angle for each photo. A shiny ball in the frame records where the light was each time. Software then combines the photos so the surface can be re-lit from any direction, which brings out the depth and shape of the cuts.

For this set, 35 photos were taken in October 2026 and 30 were used. The other five had no clear highlight on the ball.

What it shows

The letters were cut as V-shaped knife strokes with angled walls and ragged, torn edges. A long, thin straight scratch runs from the top of the “A” past the “D,” and there are a few small dents nearby. Both are visible in ordinary photos too. The re-lighting did not reveal any hidden letters, initials, or other marks.

The TAD carving in ordinary even light — Ordinary even light: an average of the photos.

The TAD carving lit by low raking light — Low raking light from one side.

The TAD carving lit by low raking light from another direction — Low raking light from a second direction.

The TAD carving lit by low raking light from the opposite side — Low raking light from the opposite side.

The TAD carving lit by low raking light from a fourth direction — Low raking light from a fourth direction.

Specular-enhanced view of the TAD carving — Specular enhancement: the surface shown as if it were glossy, to bring out the shape of the cuts.

Surface-normal map of the TAD carving — Surface map: colors show which way each spot of the surface faces.

Explore it yourself

Download the RTI file, tad.ptm (about 3 MB), and open it in the free RTIViewer from Cultural Heritage Imaging (Windows or Mac). Drag the light around to see the carving from any angle. In the viewer the letters appear upside down, the way the camera saw them.