can be opened and reclosed at will. The only drawback to this type of package is that labeling can be difficult. Sampling collection will "vary primarily depending on the type of substrate encountered. In order of typical frequency, substrates include wood, plaster materials, wall coverings, hard masonry materials, and metals. The samples are collected using a sharp metal blade such as a scalpel or XActo knife." Although actual parts of a building are submitted for analysis, the sample need not be large at all as it is viewed through a microscope. In this case, size does not matter. What is needed is a sample with all of its paint layers well adhered to each other and to their respective substrates. For most sampling methods the scraping method is utilized to take a sample to the substrate and associated varnish. When removing a paint sample, it is important to also remove a piece of the substrate to ensure the stratigraphy collected is complete. To identify different pigments, binders, and colors within historic architectural sites, "Experts use a combination of mechanical and chemical investigations to reveal the hidden layers, while a microscopy lab analysis of the layers and substrate is used to define original colors and finishes." The traditional method of carrying out a "scrape" using a scalpel is a slow and very inaccurate method of exposing the earlier layers. The disadvantages of the former technique are that given the relatively low level of magnification it is easy to miss critical layers and to misidentify layers such as primed coats as being historic finish coats. Also, the variable light sources on site alter the perception of the colors to varying degrees. It is often more effective to make a small crater with a knife and then to sand the edges to a gradual slope, the paint layers widening as the surface is rubbed down. The finished result will look like a bulls-eye, or target, with the full sequence of coats revealed. In past and recent analysis, paint researchers have become increasingly aware that the samples removed from the site for study may not represent the true historic color. Due to this inaccuracy in traditional sampling methods, architectural paint research had developed into material science. Agents of deterioration Conservation scientists rely on the chemical properties of pigments to correctly identify and age pigments within historical paint analysis. However, analysis of pigment reaction differs