Cultural property imaging

Cultural property imaging is a necessary part of long term preservation of cultural heritage. While the physical conditions of objects will change over time, imaging serves as a way to document and represent heritage in a moment in time of the life of the item. Different methods of imaging produce results that are applicable in various circumstances. Not every method is appropriate for every object, and not every object needs to be imaged by multiple methods. In addition to preservation and conservation-related concerns, imaging can also serve to enhance research and study of cultural heritage.

One reason for imaging objects is to make the items available for study and scholarship without incurring unnecessary harm to the object. In addition to providing images to scholars, images can also be added to online catalogs and databases to increase the size of the audience interacting with the objects and allow them to view the item with no added risk.

Another reason is for documentary purposes, especially as it relates to conservation. According to the American Institute for Conservation, "Documentation is basic to the ethical practice of conservation." Imaging prior to conservation allows conservators to record the current state of the object, which can then be compared to later images following conservation. This allows someone in the future to look back and see the ways in which an item was impacted by conservation. Images taken over different periods of time can also reveal changes in condition and can be used to minimize damage going forward. The American Institute for Conservation's Guide to Digital Photography and Conservation Documentation is a useful reference guide for the application of digital imaging to the field of conservation. It details guidelines for equipment, techniques, and practices that are in line with best practices for conservation. This covers everything from suggestions for types of cameras and memory cards to discussing processing details and how to apply metadata.

An additional purpose is found in the way imaging enhances scholarship. Different types of imaging can reveal materials and techniques used in creating an object that are not immediately evident with the naked eye.

There are many methods that are employed in imaging. These may include different types of lighting as well as the use of radiography. Multiple energy levels and technologies have been used for cultural heritage imaging, including imaging mummy masks with multiple spectral bands of light, different x-ray technologies, optical coherence tomography, and terahertz imaging. Photographing objects under standard conditions is a typical practice to preserve the item in perpetuity, but not every object will need more specialized imaging. Those doing the imaging or requesting the imaging be done will look at each object on a case-by-case basis to determine the usefulness of specialized imaging. In some cases combinations of different types of imaging will be more effective than one type on its own. This can be seen in projects like the Getty's conservation of Guercino's Jacob Blessing the Sons of Joseph and the Getty's APPEAR project, details of which can be found on a blog by the Penn Museum's Artifact Lab.

Photography under normal illumination will produce a record of the appearance of an object in standard conditions. Standard conditions typically mean uniform illumination with minimal glare. In conservation, these images will serve as a "before treatment" record. They can also serve as a catalog image for in-house use or an online collection. Following a standard image capture, subsequent images can be taken under various conditions to highlight areas that need treatment or closer monitoring.

Raking illumination highlights texture on the surface of an object. This is achieved by using a single light source at a low angle relative to the object. Images taken under these conditions can reveal deviations in the surface of an object – gouges, scratches, paint loss, bulges, and more. With archaeological objects this may reveal how tools were made or how food was processed (e.g. cut marks on bones). In paintings it can show how the artist used the paint.

Specular illumination documents the surface sheen of an object. With paintings, it is used to highlight areas of abnormality. While raking illumination will produce a record of these abnormalities with greater clarity, specular illumination is less dependent on the orientation of the light. There are two basic setups for specular illumination – axial and oblique. An axial setup requires the camera and the light source to be on the same axis. The camera is parallel to the surface of the object, and the light source is next to the camera. An oblique setup requires the camera and the light source to be on opposite sides of the subject, but each are at the same angle relative to the object. Specular light can allow conservators to see tool marks on wooden objects, or indentations that seemed invisible.