Documentation is part of every conservation assessment or treatment and photographic documentation —the capture of accurate images —is the core of the process. Winterthur has changed from traditional photography to digital image capture and storage following the guidelines laid out by the American Institute for Conservation (AIC). Because these images become part of the permanent record of an object, the digital files are processed and stored using the most permanent formats and methods available.
Before and after conservation treatment each object is photographed to record its condition and all visible damage and repairs; these images usually include both overall views and details. Additional photographs may be taken during treatment, particularly before inpainting or other forms of compensation. To record damage as accurately as possible, photographs may be taken in both reflected and raking light. Raking light reveals texture and planar distortions. Special equipment and procedures are used for highly reflective objects like silver or very large objects like quilts.
Special lighting such as ultra-violet, infrared and x-ray may be used to produce images that reveal details not visible to the naked eye. The varying fluorescence and absorption of ultra-violet light often reveals repairs, overpaint and other changes and anomalies in the surface of paintings, ceramics, and prints. Infrared may reveal images just below the surface such as underdrawing or make faint graphite inscriptions on a piece of furniture more legible. High energy x-rays penetrate through objects revealing interior structures by recording varying densities. X-rays reveal old repairs and the joint structures within furniture, archeological objects below layers of corrosion, and the changes artists made as they painted an image on canvas.