scrape must then be exposed to UV light for a period of time in order to clean up the color. Pigment and media identification will be carried out with the aid of a number of The evaluation of the cleaned-up color may be made by comparison with trial batches made up using the identified pigments. The primary purposes of analysis are to determine historic finishes and to determine principal components including media and pigments. There are two methods in the preparation of paint samples for microscopic analysis. The first is to mount the sample in a permanent medium such as paraffin or resin. The specimen is then ground to a flat finish, providing a horizontal surface for viewing layers in cross-section under a microscope. Samples are ground by mechanical methods to best reveal the paint layers. The second is to leave the samples in a loose condition with their broken surfaces which then can be manipulated under the microscope to permit a variety of views of the layers. It is often possible to see sequences of paint layers resulting from decades of decoration and identify color schemes in chronological order. Samples from different features of a room or building can be compared to tabulate changes in decoration on different features within successive schemes of interior decoration, revealing changes in fashion and taste. Samples from newer elements of a building will have fewer paint layers. Paint analysts are usually well-qualified to report on historic phases of decoration, architectural changes, and historical paint materials and craft practice and input into the presentation and interpretation of heritage buildings. Laboratory analysis Finish exposure Finish exposures are performed by carefully removing over-paint in order to reveal historic colors and patterns. This can be done mechanically and/or with chemical strippers. Finish exposure is useful "to uncover potential hidden artwork or patterns, and will often tell us the whole story of a historic decorative scheme." Optical microscopy Optical microscopy is capable of resolving the coarse to fine (50-2mμ-m) particles found in historic paint, thus they can be identified unambiguously in most cases. This size range affects surface appearance. Polarized light microscopy (PLM) Polarized light microscopy illuminates parts of a sample using polarized light. The technique provides reliable and compound-specific particle identification, it is high-resolution in the sense that a single particle among hundreds of different ones may be identified accurately, and it is also selective. Pigment identification