Palettes, which were the most consistent offering, were made of thin schistose rock. There is a clear differentiation between the center portion and the border which is ornamented with grooves. Some have sculptured edges in the form of birds, snakes, and other animals. There are also effigy types in which the outline of the palette is in a life-form. Palettes were most numerous early in the Colonial period and later declined in importance. One extremely interesting feature of many of these objects is that on the mixing surface of heavily burned palettes from cremations is found a vitreous substance which, on analysis, proved to be a lead mixture. It is not certain whether the use of lead ore was intentional or accidental, but in any case the Hohokam never learned to exploit this as metal. It has been suggested that the change in the lead mixture from a dull color to a brilliant red with metallic globules may have been observed as the palettes burned on the funeral pyres and that it came to have a ceremonial significance. It is entirely possible, however, that the palettes had simply been used for grinding a compound containing lead, which was used to provide pigment, prior to the burning. They may have been used to mix facial or body paint. Some of the most remarkable stone work found in Hohokam sites consisted of mosaic plaques or mirrors inlaid with angular pieces of iron pyrites which had a reflecting quality. These were common funerary offerings, and as a result most of the specimens obtained are badly damaged. None the less, one can still appreciate the amazing work which went into their construction. These plaques or mirrors range between three and eight inches in diameter. On one surface are thin sheets of iron pyrites crystals carefully fitted together. How these thin plates were obtained is a complete mystery, for pyrites crystals are usually cubic and so hard that they cannot be scratched with a knife. In some cases the crystal encrustation covered the entire face, in others edges were beveled. Edges and backs were sometimes decorated with something which resembles cloisonné work, although the technique differed. First a base coat of a gray material was applied, and then this was covered with a thicker layer of some black substance. A design was cut into this with a sharp implement, and then the sunken portion was half filled with thick white paint. Next, paint in a variety of colors was added to fill the depression, or, in some cases, was even built up slightly above the level of the black background portion. These mirrors are almost exactly like those found in sites in Central America. It is thought that the best examples found in Hohokam sites were imported from the south,[59] although it is possible that some crude imitations may have been made by the Hohokam themselves. The material necessary would have been available to them, for sizeable pyrites crystals are found near Tucson.