The many examples related above should provide the rubber analyst with systems well suited to some of his problems and, if not, certainly with direction for the evolution of custom systems for his specific needs. The Rƒ values and colors resulting from the chromatographic conditions employed by the experimenters have generally been well related for the compounds examined. These values and colors are useful as guides to another analyst but cannot be trusted for reliable identifications. Rƒ values are difficult to reproduce from one laboratory to another since the factors influencing Rƒ are not always readily reproduced within the different laboratories. Colors are difficult, if not impossible, to describe accurately or to reproduce faithfully with color photography. In addition, many colors may vary (some quite rapidly) with time after or conditions of indication. An identification is best and most reliably made by comparison to known compounds. An unknown is identified when, after adjusting the sample spot size to match that of the known, it travels the same distance and gives the same color and shape as the known. The use of a chromogenic indicator is advisable, if one suitable is available, since differentiation of samples by both a wide range of colors and Rƒ values makes identification much easier. TLC has been shown to be of great utility for the identification of rubber compounding ingredients by the many examples related above. In addition, TLC has proven a rapid, reliable, relatively simple, and inexpensive technique. Undoubtedly many new papers will appear in the future. Some will enlarge or improve on applications already existent. Hopefully, a quantity will tap areas of rubber analysis yet untouched by TLC.