HPTLC uses plates made from silica or special plates known as concentration zone plates. The concentration zone plates are made by covering a glass or plastic support with a layer of an inactive and very absorbant substance such as Kieselguhr or synthetic silicon dioxide with large pores. The inactive layer slows down the initial movement of the sample under study and concentrates the sample, and the active layer separates the constituents of the sample. The results provided by HPTLC are comparable to those of liquid chromatography, while it has the advantage of requiring only small amounts of the sample substance (which would be insufficient for liquid chromatography); however, only semiquantitative measures can be obtained with this technique, since it is impossible to determine exactly the mass of the ink contained in the sample. When two inks are compared, two ink strokes of similar size should be taken and dissolved in the same volume of eluent. The concentrations obtained, if not identical, will be easily compared. The slight difference between them will be indicated by a small shift of the curve in relation to the vertical coordinates, but their profiles will be similar. Overall, the method can be expected to improve examination techniques and provide increased precision in comparing inks. Photographic illustrations are provided, along with three bibliographic listings.