One of the most distinctive features of the Chacoan system was the widespread production of black-on-white pottery decorated with designs involving closely spaced parallel lines. This type of design, known as “hachure,” is typically used to fill large spaces outlined by thicker lines, in much the same way that such spaces are also often filled by solid black. Hachure is characteristic of several “types” of pottery closely associated with Chaco, such as Red Mesa Black-on-white, Gallup Black-on-white, and, characterized by exceptionally fine and well-executed hachure, Chaco Black-on-white. The distribution of these hachured types corresponds pretty closely to the distribution of Chacoan great houses and other features of the Chacoan system, although it does extend further west than the other features, into the Kayenta area where it is known as “Dogoszhi style.” Indeed, hachure is extraordinarily widespread throughout the northern southwest during a quite short time period (roughly the mid-to-late eleventh century), and it’s not entirely clear that it has a direct connection to the Chacoan system which also flourished during this period. Still, because many of the most spectacular examples of hachured ceramics were found at Chaco Canyon and the style does seem to have been particularly common there, it seems likely that there was some connection between hachure and Chaco, though that connection may have been different from the relationships represented by, e.g., great-house architecture.
Given this strong association, it is tempting to think that intense study of hachure and its possible meaning(s) can shed light on some of the more abstract aspects of the Chacoan system that are otherwise extremely difficult to understand. The generally abstract nature of Puebloan pottery decoration, especially during the early periods, tends to discourage scholars from attempting much detailed analysis of the possible meanings represented by the designs, which I think in general is a sound approach. In the specific case of hachure, however, I think there is room to look a little closer.
One archaeologist who has done so is Steve Plog, of the University of Virginia. He recently published an article arguing quite persuasively, largely from comparison to the patterns of decoration on other items, that hachure represents the color blue-green on ceramics that, for technical reasons relating to the process of firing, could not be painted blue-green directly. He further associates this color symbolism with the clear importance of turquoise in the Chacoan system, and even points out examples of lapidary decoration in which turquoise, jet, and shell fulfill decorative roles eerily similar to those filled by hachured, solid, and background elements in pottery decoration.
Plog does not distinguish between blue and green for a variety of reasons. Among the most imporant of these is that many (but not all) modern Pueblo languages do not distinguish between the two, which is actually pretty common cross-linguistically and also the case in, e.g., Navajo. Turquoise also varies in color between bluish and greenish, both naturally and depending on how it is prepared for use in decoration. And, equally importantly, the Chacoans seem to have very rarely used blue and green together in decorative designs, suggesting that they did not make a distinction between the two.
All this seems quite convincing to me, and I think Plog makes an extremely strong case for his proposal. Color symbolism, as he points out, is very important to the modern Pueblos, and there is every reason to believe that the same was true for their ancestors. And, it seems, when technological limitations kept those ancestors from expressing colors directly in all media they developed an effective system for symbolizing at least one color in a monochrome context.