Archaeologists are continually misunderstanding the white slip on Salado polychromes. The oft-repeated theory that the black organic paint on Salado polychromes is achieved through low temperature firing is wrong, or at least partially wrong. The firing temperature might be lower than some other southwestern pottery but on the whole I would suggest no lower than most other pottery of the southern Southwest (Hohokam, Mogollon brown wares, other Salado potteries). Remember too that Salado polychromes require a firing temperature high enough to property oxidize the reds, fire clouds on these ceramics are evidence that the firing temperatures reached these levels.
The organic black on Salado polychromes is special but many archaeologists have missed the source of that specialness. Salado Polychromes, especially those polychromes based on organic black pigment (Gila Polychrome, Tonto Polychrome, etc), are the most distinctive defining characteristics of Salado culture, other cultural elements vary widely from one side of the Salado sphere to the other, but these polychrome wares are consistent across the area. For example, Salado in the Tonto Basin buried their dead, while those in the Sulphur Springs Valley cremated, some had doors in their houses while other areas had rooftop entries. Salado polychromes were a phenomenon that spread rapidly and widely, this phenomenon was based largely on black organic pigment on white slip. Those not involved in traditional southwestern ceramics may not be aware that white clay is extremely rare in this area, so rare that in most areas of the southern Southwest, Salado polychromes were the first examples of pottery with white areas ever produced there.
While white clay is rare, white clay that will accept a vegetal paint without firing out is even rarer. Take the example of Cochiti slip. Cochiti slip is a bentonite clay, originally coming from Cochiti Pueblo, that holds onto vegetal paint in an oxidizing atmosphere, this allowed the Indians to create beautiful polychrome vessels with bright reds and dark blacks. This slip produces results very similar to those seen on Salado polychromes, a dull, unpolished white or cream colored surface. This slip was so valuable that its use spread to other pueblos, in time those pueblos were willing to pay Cochiti for the right to gather this clay from their lands. For many years Cochiti slip provided the foundation for many of the polychrome wares produced by the New Mexico pueblos. In the early 1970s, with the filling of Cochiti Reservoir, the primary source of Cochiti slip was lost beneath the waters. A smaller source on Santo Domingo Pueblo lands lasted for a few more years but, I am told, that source has now been depleted. New Mexico Pueblo potters have searched for a replacement but none has been found, this situation illustrates the rarity of a white clay that will retain a black organic paint in a oxidizing atmosphere. From personal experience I can say that the situation is no better here in southern Arizona in Salado country.
The secret to the magic that is Cochiti slip is the Bentonite clay. Bentonite is well know for its absorptive properties, these properties allow it to absorb the organic paint and lock it away so that, although it carbonizes in the firing, it does not fire completely out of the clay in an average firing. Having tried a large number of the native bentonites in southern Arizona, most of them will not fire white, the lightest of them tend to fire yellow, and they don’t make a good black out of the organic paint, but tend towards a grey color. The scarcity of good white bentonite slips that will make a good black organic paint just shows that the Salado must have relied on a good trade network to deliver quality white slips throughout the Salado area.
The strength of the Salado trade network is well illustrated by the Salado obsidian trade. Some things are easier to source than clay slips, rocks for example. When archaeologists are sourcing pottery they have more success sourcing the tempering in the clay, usually ground rock or sand, than the clay itself. Recent archaeological work in the Mule Creek New Mexico area has identified the obsidian there as the primary source of obsidian used throughout the eastern Salado area, clear to the Mexican border and across southeast Arizona. So this one source of obsidian was traded miles and miles across the Salado area. The Salado must have had a vibrant and active trade network to supply literally hundreds of villages with obsidian from the Mule Creek area. No doubt the rare white bentonite clay the Saladoans used for their polychrome pottery depended on that same trade network for delivery from its source or sources.
Archaeologists, as scientists, tend to rely on tests like the refiring test to prove things. There is nothing wrong with a refiring test but it is no replacement for actually testing your theories by trying to recreate the prehistoric potteries, which is the next logical step to prove these theories. Pottery is first of all an art form, and sometimes to understand it fully you have to think and act more like an artists than a scientists. Archaeologists studying southwestern ceramics almost always stop short of this final step of full recreation in proving their theories, probably because they perceive they have reached the boundary of science and art and are hesitant to cross that line. This is the critical, and missing, next step to understanding Salado polychromes. One can speculate and theorize about low temperature firing on kaolin clays (http://archaeology.asu.edu/vm/southwest/salado/text.htm) based on refiring tests, but in the end it’s only a theory until you can prove it by actually recreating the pottery type. There are various reasons why a refiring test cannot duplicate the conditions of the original firing. What is needed is not a refiring, since prehistoric southwest potters generally only fired ceramics once, but a firing test which implies reproduction with fresh materials.
I have pointed out this bentonite – Salado polychrome issue to several archaeologists in recent years and received little apparent interest, perhaps duplicating the results of the ancient Salado potters will convince somebody that I am onto something. Today I conducted a test firing of several new white slip sources and I have positive results from a white slip obtained from within a volcanic ash deposit in Benson, Arizona. This firing was not especially low temperature as the accompanying photos will illustrate, the temps were high enough that I got numerous pops from pyrite in the temper of some of my vessels, this indicates temperatures in excess of 600° Celsius. The accompanying photos show the results of my test firing, my next step will be to create a full Gila Polychrome bowl to demonstrate that it can be done, stay tuned.
Notice the sparkles in the Benson white, similar to that found on Salado white slip. The yellow color and crazing of the San Manuel clay is typical of Southern Arizona bentonite deposits. Notice the pyrite pops on the square tile, the tempering on this tile was wash sand from Canada del Oro wash near Thornydale Road in Tucson, the pyrite produces sulphur gas at temperatures above 600° Celsius, an indication of my firing temperature. The paint on both tiles is mesquite syrup (boiled down mesquite beans).