The earliest and most primitive Greek vases (including those of the Mycenaean period) in most cases exhibit the natural quality of the clay, ranging from yellow to grey in colour; it is usually coarse and insufficiently baked, and protected by no lustrous glaze. In the early archaic vases, such as those of Melos, Athens, and Rhodes, we observe a pale yellow tone, which is apparently not a glaze, but inherent in the clay.[742] Thenceforward the clay becomes appreciably redder and warmer in tone until the lustrous glaze reaches its perfection in the Attic vases of the fifth century. In the later Italian fabrics again there is a great degeneration, the clay rapidly reverting to a paler hue, especially in the vases of Campania; while in the Etruscan imitations of the third century it is a dull coarse yellow, apparently due to a preponderance of lime. Generally speaking, it may be said that the colour depends on the proportion in which the constituent parts are mixed, a larger proportion of iron oxide producing a redder, a larger proportion of lime a paler hue. The clay is permeable, allowing water to exude when not glazed, and when moistened emits a strong earthy smell. It is not known how this paste was prepared, for the Greeks have left few or no details of their processes, but it has been conjectured that the clay was fined by pouring it into a series of vats, and constantly decanting the water, so that the last vat held only the finest particles in suspension. The clay was worked up to the right consistency with the hands, and is supposed to have been ground in a mill or trodden out with the feet. Either red or white clay, or a mixture of the two, was preferred by the ancients, according to the nature of the pottery required to be made, as we learn from an interesting passage in the _Geoponica_:—“All kinds of earth are not suited for pottery, but some prefer the reddish variety, others the white; others again blend the two ... but the potter ought personally to assist in the operations and see that the clay is well levigated and not placed on the wheel until he has obtained a clear idea of the probable appearance of the jar after the baking” (vi. 3).