Paints optical microscopy

Scanning electron microscope (SEM) systems are ideal for a pictorial representation of morphological features of single layers of multilayered paint samples (particularly those not well contrasted by optical microscopy as the white ones) obtained by the contrast of secondary (SE) and backscattered electrons (BSE). An important advantage of SEM is the ability to analyze even the smallest smears for this purpose the smears are lifted from the underlying material using double-sided adhesive tape transferred to the sample holder (e.g., slide). Twenty micrometers microtome sections of paint cross-sections are recommended. In order to avoid electrical charging the samples have to be carbon coated or transferred into the chamber of a low vacuum system. 

Govaert, R, and M. Bernard. "Discriminating Red Spray Paints by Optical Microscopy, Fourier Transform Infrared Spectroscopy, and X-ray Fluorescence." Forensic Science International 140 (2004), 61-70. 

Optical Techniques. The most important tool in a museum laboratory is the low power stereomicroscope. This instmment, usually used at magnifications of 3—50 x, has enough depth of field to be useful for the study of surface phenomena on many types of objects without the need for removal and preparation of a sample. The information thus obtained can relate to toohnarks and manufacturing techniques, wear patterns, the stmcture of corrosion, artificial patination techniques, the stmcture of paint layers, or previous restorations. Any art object coming into a museum laboratory is examined by this microscope (see Microscopy Surface and interface analysis). 

Studies of art works both for pigment identification in paintings using LIBS and Raman microscopy [177] and for on-line optical diagnostics [178] have recently been reported. 

Two reference methods are recommended for painted surfaces a method in which the surface profile is measured (ISO4518) and a microscopy method (ASTM D 2691) for coatings on wood and other substrates. Other optical methods include the wedge-cut method and the profile-measuring microscope method. 

Then, microscopic examinations follow optical research microscopes allow to determine the number, thickness, and color sequence of layers in paint fragments, and to recognize the textures as well as fundamental features of pigment and extender mixtures. Bright field and dark field illuminations, polarized light microscopy (incident and transmitted), particularly the differential interference contrast (DIC) procedure, and fluorescence microscopy are necessary for paint examinations (see Figure 3(A)-3(E)). 

Examination of specimens in UV light requires the use of optical components capable of transmitting such short wavelengths, which means the use of quartz rather than glass lens components. However, when combined with a UV spectrophotometer, this enables the analysis of small areas of a sample by UV reflectance, absorption, or transmission. An example of this is the identification of materials used by the artist in a painting. The use of UV microscopy for enhanced resolution has been entirely superseded by transmission electron microscopy. 

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