Unknown Title

Unknown Artist

Intro

Doing preliminary investigation on a cultural object serves to just one scope: raising questions.

Is there any sign of previous conservation treatment? Can we map them out? Is that pigment consistent with the artist’s palette? Is there something that we can’t see at a first glance? The more answers we find, the more questions raise and the more we know about that object, its author and its cultural value.

To answer these questions, photographic and computational imaging techniques can be used as a non-destructive analysis that provides informative results.

According to the object’s nature, its properties and the questions you want to answer, the choice of the techniques to use and their combinations may vary considerably.

In this page we share with you a basic application of some techniques used on an oil on canvas, a subject of which nothing is known -yet.

Colour Photography

This is the first image to take: a base on which the subsequent observations are made.

 A faithful reproduction of colours, tones and details is the main goal.

Oil on canvas / 66.3 x 49.4 cm / Private collection

Infrared

Infrared Photography exploits the optical properties of pigments, which may reflect, absorb or transmit the infrared radiation at specific wavelengths.

It’s a “must have”, as it penetrates the paint layer and reveals the preparatory drawing (if any).

Infrared False-Colour is the result of the combination of the IR photograph and the visible colour image.

It comes in handy to get a first, broad discrimination of pigments and metamers.

Infrared photography / Infrared false colour image

Enhancement

The Chromatic Image is obtained from the colour image by subtracting the luminosity: what remains is a map of the hues.

The image is particularly useful when features in the dark areas want to be enhanced, revealing details otherwise difficult to spot.

The Chromatic Image can also be coupled with the IR photograph, to further investigate the presence of overpaints and pentimenti.

Chromatic image / IR chromatic image

Morphology

The surface morphology can be investigated in several ways, according to the needs.

The Raking Light image is the simpliest, and most common option to get an overview of the overall surface.

When a closer, more detailed inspection is required, RTI (Reflectance Transformation Imaging) is more suitable.

Raking light
Normal map of the surface obtained from RTI reconstruction

Structure

Transmitted Light Imaging can be performed on some paintings on canvas.
The visible colour image enhances the weaving, tensions and holes.

Infrared Transmitted Light Imaging may be of help in identifying the presence of underpaint and hidden marks. 

Transmitted light image / IR transmitted light image