Black-on-white Potsherd at Kin Bineola
“Never read the comments” is generally sage advice, so it’s likely that many of my readers have missed the interesting comment thread in response to my previous post. I won’t try to summarize it all here, but the gist is that a potter showed up and took issue with my use of the word “paint” to describe the pigments applied to prehistoric Pueblo pottery. Apparently, while archaeologists routinely refer to these pigments as paints, that’s not actually an accurate characterization and they are instead best described as types of “slip,” a term that archaeologists usually use only for the underlying layer of thin clay that the “paints” are often applied to. There’s a long history of archaeologists appropriating and misusing terminology from other fields, so it’s not surprising that they would have done this in this case too, but I’m not sure how best to proceed with the terminology, as it is pretty useful in practice to be able to distinguish the underlying “slip” from the “painted” designs on top of it. For now I’ll try using the (hopefully) more neutral term “pigment” for the “paint” and continue to use “slip” for the underlying clay.
Another issue that came up in the discussion, however, is separate from the terminology. This is the question of how the carbon-based pigments that are so well known from many parts of the Southwest could have adhered to pots after firing at all. After all, at the temperatures necessary to create usable ceramics any purely carbon pigment would burn right off. As I started to think about it, I realized that this was indeed a puzzle, and I went looking back into the literature to see if it had been addressed anywhere.
As it turned out, it had, and in the very first research on this subject, that of Florence Hawley in the 1920s. Hawley was an important figure in Southwestern archaeology throughout much of the twentieth century, and her early chemical studies of pottery pigments were fundamental in establishing the classification system by which they have been interpreted ever since. The most important aspect of this system was the division between “carbon-based” and “mineral-based” black pigments, although looking back at her initial publication on this topic from 1929, it’s clear that the dichotomy is more subtle than the terms imply. In fact both types of pigment contain both carbon and mineral elements, the difference being the relative proportions and the specific minerals involved. Both involve the boiling of certain plants, usually Tansy mustard or Rocky Mountain beeweed, to create a thick, black substance that can be applied to an unfired pot with a brush. The carbon type consists only of this substance, while the mineral type involves a subsequent step of adding ground iron oxide before applying it to the pot. Hawley also identifies a third type using manganese, which she speculates was used for certain types of pottery made of clay to which the usual carbon pigment wouldn’t adhere properly. (She also identifies a fourth type, so-called “smudged” pottery, that resulted from adding organic material after firing and letting it sink into the clay. This type is generally associated with the Mogollon culture in the highlands of east-central Arizona and west-central New Mexico and is quite different from the others in appearance.)
The chemical tests Hawley suggests to distinguish among these types of pigment are complicated and involve the use of dangerous acids, so they have not caught on as routine methods for archaeological analysis in more recent years. The tests appear to have been worked out and conducted mainly by Hawley’s father Fred Hawley, who was a chemist at a smelter in one of the mining areas of Arizona. Instead of these tests, archaeologists have generally tried to learn to distinguish the more common types by sight. As one of the papers I discussed earlier found in a test of this method, it works pretty well except in more marginal cases that are difficult to interpret using the standard visual criteria. The methods that have been proposed more recently using modern imaging technology have also not yet become very popular. In general the visual criteria seem to work fine.
As I noted in the previous post, the fact that both organic and mineral pigments seem to work to create black designs, but the mineral type is basically the same as the carbon one, raises the question of why there were two types at all. I suggested that cultural tradition rather than technological considerations probably was the main factor. Hawley doesn’t address the question in those terms, but she does argue that the different pigment types correspond to different cultural traditions, and the second half of the paper consists of her conclusions about cultural provinces and their spheres of influence based on pigment types through time. Her basic scheme of carbon pigments predominating in western areas and mineral pigments further east has generally held up, but otherwise her interpretations show how little was known at the time about Southwestern prehistory. She was clearly writing before tree-ring dating had established a firm foundation for the absolute chronology of cultural developments and pottery types, and the assumptions she makes about which sites were contemporary are strikingly wrong in light of that chronology. This makes her conclusions about changing patterns of cultural influence through time basically useless.
All that said, what about the question I mentioned earlier? How does the carbon pigment survive firing? Hawley’s answer, backed up by the chemical tests, was that it actually contains some mineral inclusions in addition to the carbon, especially silica and carbonates that melt in the process of firing and form a very thin film over the carbon that protects it from burning away. She considers this layer too thin to be considered a glaze, but it appears to serve the same basic function. It only works, however, when firing is in a reducing atmosphere, i.e., with oxygen prevented from reaching the surface of the pot. It’s not totally clear from her explanation where these mineral compounds come from, but the implication seems to be that some are from the plants from which the pigment is made and others are perhaps from the clay of the underlying pot. In the case of the mineral pigments, these potential sources are complemented by the trace silica in the iron oxide. As the more recent papers note, this interpretation has been questioned by others, most significantly Anna Shepard (another pioneering ceramic analyst at the same time as Hawley). It seems clear, however, that getting these pigments to survive firing requires some sort of chemical reaction along these lines, involving compounds in the pigment and/or the clay, along with a reducing atmosphere during the firing process itself.
It turns out pottery is pretty complicated! Archaeologists usually use pottery types primarily as a means to date sites and establish trade relationships, but studying potsherds intently with an eye to technological issues can reveal a lot of additional and potentially useful information.
Hawley, FM (1929). Prehistoric Pottery Pigments in the Southwest American Anthropologist, 31 (4), 731-754 DOI: 10.1525/aa.1929.31.4.02a00110
When I worked at the Park Service as was given time to study extensively about prehistoric ceramics I read both Hawley and Shepard and found myself drawn back to both on a regular basis to try and gain some insight into the process. As a rule I found Shepard more useful and also less friendly i.e. she offered a greater range of readable material but her research was concomitantly more global than the narrow collection I was involved with.
At this time I would argue against trying to change the terminology. In my experience archaeologists are surprisingly conservative when asked to change something that they have held as rule for some time. Perhaps that is due to their inherent insecurity of having based their entire professional careers on their best guess. In this I am including myself. Though I have not engaged in ceramic analysis per se since the mid 80s I would be loath to discard the term paint as referring to the decoration of a vessel and the term slip as the overall coating, whether clay or pigment based.
Current ceramic analysis seems to be mostly focused on layout and design elements ascribed to tradition and implications of anthropological issues such as cosmology, and/or clay sources and firing dates as assessed by techniques such as thermo-luminescence but there may come a time where the discussion shifts back to the elements of paint creation and application and then a change in nomenclature might be effected.
I haven’t read any of Shepard’s work, partly because it’s pretty hard to find. Many of her important publications seem to have been chapters on ceramic analysis in important site reports (such as the Pueblo Bonito one where she famously argued from the presence of trachyte temper that much of the pottery was imported, which pissed off Judd so much that he included a rebuttal of his own). Hawley, on the other hand, published prolifically in major journals, so I have lots of her publications easily available. I have the same impression, though, that Shepard was actually a better ceramic analyst, if not as accessible as Hawley.
That’s fair enough on the terminology point, and I have no intention of trying to change the practice of archaeologists, who I’m sure will continue to use the term “paint” regardless of what I say. I’m not an archaeologist myself, though, and this blog isn’t primarily targeted at archaeologists either, so it’s pretty easy for me to just change my own usage as a gesture of acknowledgment to the potters. Of course, having said that I’m sure someone will come along and object to the term “pigment” on some other basis, and then I’ll be back where I started.
Anna O. Shepard, Ceramics for the Archaeologist, 1950, I think. I don’t know for sure like I said I haven’t studied in years. Here is an online copy: http://profesores.usfq.edu.ec/fdelgado/Teor%C3%ADa%20y%20Métodos%20en%20Arqueolog%C3%ADa/Archivos%20Digitales/metodos/Shepard%20Ceramics%20for%20the%20Archaeologist.pdf
As far as someone coming along and criticizing what you say, in archaeology that is the norm, not the exception.
Thanks! And yeah, I know criticism is inevitable, but I still don’t like it.
Very interesting subject. I have been doing research in just this area by collecting clays and firing them in open mesquite fires. While it is easier to keep carbon based paint on a pot in a reducing atmosphere this doesn’t account for polychromes. To make polychrome with a carbon based paint, like the ubiquitous Gila Polychrome, requires an oxidizing atmosphere. Certain kinds of clays have the ability to hold these carbon paints through a firing, bentonite clay in particular. Modern pueblo potters have used a slip called Cochiti slip which has these properties, ancient potters in cultures such as the Salado had access to similar slips. If you look at my blog you will see posts regarding this research.
That’s interesting, Andy, and from a quick glance at the relevant section in Marc’s link it looks like Shepard’s explanation for the carbon persistence was the same. She also did some experiments that seem to have effectively disproven Hawley’s theory.
Andy, my experience with betonite indicates it does not adhere well and when fired it often crumbles. If you read the comments on teofilo’s previous post, certain igneous materials seem to be a better candidate for the crazed slip of Gila polychrome. What is your blog address Andy?
Andy’s blog appears to be linked from his name. There’s some interesting stuff there.
Bentonite tends to have extreme shrinkage rates so it can be problematic, but it does vary from source to source and it can be mitigated some by tempering. Take a look at the pictures of the test tiles on my most recent blog post, I believe my results are very close to Gila Poly. If you are referring to the volcanic ash at New River I am aware of this source and have used it myself. Bentonite is formed from volcanic ash so the material at New River is probably similar. However the New River source is too far from the Salado heartland to be the source of that slip in my opinion.
My blog is http://www,palatkwapi.com
I guess it depends on where you consider the Salado heartland to be Andy. The Tonto Basin is probably the most likely for size of population (and strategic location for who and what they were) that is only 50 miles away as the crow flies. A fist sized chunk of ash when ground could slip 10 pots and would have been easily transported there. Considering the enormous amount of ceramics they brought into the Tonto/Roosevelt area from above the rim this would not have been unusual. The old standard of ceramics was that all the raw materials were assumed to have been found near the production area, but I do not think this holds true for slips and pigments. The temper of Gila and Tonto Polychrome in the basin indicates a local production and distribution from there out of the valley. An eastern manufacturing source also exited east of Safford but they used a different slip. Until we get a better handle on where production spots really were and the volume of pottery moved through time it will be hard to understand the dynamics of it all. If the goal is to define ethnic or trade related boundaries it takes some serious teasing out of the data. The old question of why organic paint vs. mineral has been beat to death with most conclusions being made that it did not matter. I see it as similar to the broad stylistic differences for ceramics in the southwest. If you do not get too wrapped up in the details and look at the big picture there are trends that are important.
Relshen – I agree the the Salado white slip depends on a trade network, I believe there were probably no more than a handful of sources. While they could easily trade slip from far away to produce their wares, I believe that wherever this type was originally invented (probably where Pinto Polychrome was invented) this slip is likely local. Most of the Salado research I am seeing lately points to the center of Salado culture and the area where the majority of the Kayenta immigrants landed as being near Point of Pines and the confluence of the Gila and San Pedro Rivers, quite a distance from New River.
http://www.archaeologysouthwest.org/pdf/2012_saa_poster_upper_gila.pdf
http://www.statemuseum.arizona.edu/coll/featured/perforated_plate/
I agree the first in the series was Pinto and it was made above the rim, but the later ones were not. We analyzed a lot of gila poly pottery on the Roosevelt project and it was made locally. And as a side note there is no such thing as local made Roosevelt black on white, it was also all brought in from above the rim.
I worked in Pinto Valley near Miami AZ for several seasons and we found mostly Roosevelt B/W, San Carlos R/B and San Carlos red, there was an absolute dearth of Salado wares, I think we found one sherd of McDonald. It makes me wonder about Salado as an entity or as simply an adaptation by various peoples to the montane environment. If they were primarily resource gathering them importing pottery would make sense. My friend Ric Windmiller used to refer to our sites as “Mountain Hohokam” and I kind of like the term.
If I were ever to drag my huge rusty butt back into fieldwork it would be research into what constitutes “Salado”?
However, I do have to disagree with you Reishen, at least semantically, somewhere there is a place where Roosevelt B/W is local, it just isn’t the Roosevelt basin. What about just above the Mazatzals?
Most of the vessels called Roosevelt B/W are actually either Pinedale or Snowflake. Even Salado redwares were moved down the hill as they have temper and slip from the Cibique area. Your site by Miami sounds early and lacking in Pinto poly. which would not be too unusual. Gila Poly also can be semi rare in places you would think it to be more common, such as in the lower salt/gila hohokam area. What is there seems to mostly have originated from the Roosevelt area with its characteristic multi-lithic sand temper. So there are several dynamics going on-people early on moving south and bringing pottery with them followed by a continued influx of whole vessels. Was the later stage trade, influx of people or a result of seasonal rounds, who knows.