VISUAL EXAMINATION 6. Visual Examination (May 1986) Encompasses non-sampling examination methods for support and media, surface and underlying layers, by direct or magnified observation using a variety of illumination sources and techniques. This outline is intended to provide a brief summary of the tools and techniques of visual examination as they are used to study the manufacture and condition of, and in the treatment of art and (See 2. Media Identification; 3. Media artifacts on paper. Problems; 4.Support Problems; 7. Authentication; 23. Consolidation/ Fixing/Facing, et al.). 6.1. Purpose 6.1.1 To determine the original materials of the work of art and the characteristics of these materials. 6.1.2 To determine the history of the object based on the evidence of its physical condition. 6.1.3 To determine the presence of alterations and their implications for the physical security and longevity of the object. 6.1.4 To determine the presence of components or conditions that may influence conservation treatment and to aid in the evaluation of ongoing treatment. 6.2. Factors to consider Visual examination is the first line of approach to study of an artwork because it does not require that the surface be touched. It precedes and directs instrumental analysis in which the structure and composition of the artwork is (See 9. determined by analytical methods requiring sampling. Instrumental Analysis) 6.2.1. Can provide information about the materials, manufacture and condition of the support. 6.2.2. Can provide information about the materials, structure and condition of surface media layers and, possibly, information on the internal media layers, including underdrawing. 6.2.3. Accessibility of expertise in-house or from outside resources. 6.2.4. Accessibility of equipment in-house or from outside resources
(6. Visual Examination p. 2 6.2.5. Funds available for simple low-cost techniques only or no financial limitations. 6.3 Materials and Equipment 6.3.1. The Eye as Tool/Direct Observation Encompasses direct visual examination of support and media using visible light (400-700nm), i.e. the range of electromagnetic radiation to which the human eye responds and which gives us sensations of colour, texture, transparency, etc. During visual examination the object must be seen in as much detail as possible; strong illumination is needed (cp. requirements of gallery lighting of works on paper). The human eye is very adaptable and interprets color and brightness relatively rather than according to absolute standards. Therefore, it is important to know the effects of different illumination types on visual acuity and color discrimination. Various light sources are available (see 6.3.3. Light Sources Visible Range). The object may be illuminated from one of several angles (see 6.4.2.B. Examination by Varying the Angle of Illumination). Information may be recorded photographically. 6.3.2. Magnifiers A. Hand-held Magnifiers: These consist of a single lens or lens combination. Placed between object and eye, a convex lens restores image sharpness, increasing apparent object size. Magnification is usually in the range 1.5 to 20 times. Field of view (area of object seen) is directly related to the diameter of the lens. For the largest possible field of view hold the lens as close as possible to the eye. With or without built-in light source. 1. Single Lens Magnifiers a. Pocket-sized lens that folds into an attached protective case; lens is often small in diameter, e.g. 17 to 35 mm. Reading-glass type lens: b. Usually has a large lens, e.g. 80 to 100 mm in diameter for a circular lens or 50 x 100 mm for a rectangular lens, or - Pocket-sized, e.g. a 45 mm lens. c. Magnifiers attached to adjustable desk-top stand: Lens can be up to 104 mm in diameter or sometimes greater.
(6. Visual Examination p. 3) 2. Multiple Lens Magnifiers: More complex; consist of double or triple combination of lenses designed to eliminate certain optical errors. Upper magnification limit is about x 20; usual values are x 6 to x 10. a. Magnifiers o