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technical analysis of materials

Reflectance Transformation Imaging (RTI) analysis

RTI is a technique used primarily to study degraded glass surfaces, engravings, painted surfaces and enamels. Current research is exploring how its application to glass can be further developed.

RTI captures an image of the glass surface based on the way it reflects light. Software allows various surface features to be examined virtually and documented photographically. By repeatedly adjusting the angle of illumination from an external light source positioned at a fixed radius from the object, different surface characteristics are revealed. Special filters can accentuate specific surface characteristics.


IMAGE A. Dittus, 2016, Swiss National Museum

An object is photographed multiple times with the light source positioned at the same radius from the object but at different angles. It is relatively easy to create an RTI setup, and the software is free to download (culturalheritage.org).


RTI dome built by J. Wagner during a study at the University of Amsterdam > more information   PHOTO T. Costello

RTI makes it possible to examine the surface in greater detail. As shown in the image below, the direction of the grooves, the air bubbles and the depth of the engraving become more visible. Such features can provide information about the tools used during manufacture.


Photomicrograph of engraved glass, collection R. Dick   IMAGE A. Dittus, 2016, Swiss National Museum

RTI can be used to study the morphology of a cold-painted layer on a glass surface in detail. Cracks, air bubbles, surface relief and details of the paint application can be clearly documented.


Glass bottle with cold-painted decoration, collection Franziskanermuseum Villingen.   IMAGE A. Dittus, 2016, Swiss National Museum