| Ruins Pottery! |
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POTTERY: Our Expert - Harold S. Colton - Archeologist Extraordinare Before we get started, let me introduce Mr Colton. He was not the most famous or prolific of the early southwestern archeologists, but he's our favorite (that's what matters). He and his wife moved out here to Flagstaff in the early 1900s, and began looking at the ruins sites around Flagstaff. Eventually they created the Museum of Northern Arizona for the collections, which subsequently sponsored many of the later digs (we also like their geology efforts). We're going to be using two of Harold's many writings: 'Potsherds' (1953) and 'Handbook of Northern Arizona Pottery Wares', also by Lyndon Hargrave (1937). Although much of archeology has changed through the years, surprisingly most of the early pottery classing has remained. Woo hoo! |
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An Early Potter at Work Let's start by looking at an ancient lady artist. After collecting some clay that she previously had good luck with, she takes out any of the pebbles, and then slowly adds water, until the water is about 30% of the weight. She'll knead it until it reaches the right 'plasticity', creates small 'balls' and then sets them aside for several days to 'ripen'. Later, she'll take some clay about the size of her hand, creating a shallow bowl. Next, she'll slowly add coils around the edge, building up the walls to the desire height. Using a gourd rind, she obliterates the coils and shapes the vessel. Upon completion, it is set aside to dry. When the clay is partially dry, she will then scrape the vessel again, thinning the walls and removing imperfections. When finally dry, she'll polish the outer surface with polished pebbles and another type of clay, until it almost reflects light. At this point, a painted design will be added, using a few limited minerals, and a narrow-leaf yucca as a brush. After the design is complete and dry, she'll first do a final drying with a fire near the pottery on a windless day. When all the clay water is completely removed, she then builds a 'kiln' of dung over the pottery, but not touching it. She fires the dung, and then leaves it to burn, until it is completely out (generally reaching a temperature of 800 degrees). Done! |
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What is Pottery? If you mix clay with some water and heat it to about 150 degrees, the clay becomes hard, but if mixed with water again, it resumes its plasticity. If you heat it to about 500 degrees, much of the water will fuse with aluminum silicate, and it will not resume its plastic condition with added water. If you heat it further, from 500-900 degrees, the clay particles fuse partially, sticking together and will not become soft with water. It will, however, be somewhat porous and is called 'pottery'. If you continue the heat from 1000-1400 degrees, the particles will fuse even more, closing the gaps and shrinking measurably. This is known as 'porcelain', and is impervious to water. How'd the native americans figure all this out? Good question! Back in the early 1940s, archeologists found an ancient northern San Juan college lab. Well, maybe it 'seemed' ancient. |
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Pottery Basics Clays: Technically, clay is 'hydrous aluminum silicate' with very small particles. It's not just 'dirt'! 'Residual clay' comes from a weathered limestone, combined with an acidified water. 'Sedimentary clay' comes from running water that sorts the particles, layers them, eventually creating a shale. Alluvial clays combine the previous two from erosion and is mixed with small rock fragments. This type is the most frequent you'll find on the Colorado Plateau, and fires to a light gray or buff due to any iron (red) having been previously removed by the water. For the 'red' pottery, you need iron in the clay, which generally comes from volcanic lava flows. Acid volcanic rocks, such as granite, break down into clays lower in iron and so fire to lighter reds. Now, isn't that interesting?! And if you also enjoy geology, you can pretty much figure where the native-american clay is going to come from! Often the clay is impure and not clean. How do they 'clean it'? Easy. They add a lot of water, let the impurities float off, and then remove the water. Modern potters use good clay, but in ancient times, almost any clay could be used with this method. Temper: No you're not angry! Temper, for pottery, is needed to avoid cracking, as the clay is heated. There needs to be an 'exit plan' for the water. Most often, sand, volcanic ash, or old pottery sherds are mixed with the clay, to give the water a way to exit during heating. By looking at a pottery sherd carefully, you can detect the temper used and thus more about its origen. Modeling: There has been no evidence of a potter's wheel being used in the ancient southwest. The most frequent method was in using coils, over top a base or 'cast'. Obliterating the coils varied by group, and thus its type. From a sherd, how do you tell if it's a jar or pot? In general, if the inner surface is worked similar to the outside surface, it's a pot. Jars were more utilitarian for storage and carrying water from creeks below. 'Slip': Now, we're getting technical! If the color of the pottery wasn't to your liking, you added a thin creamy solution of water and fine clay, producing a different color when fired (the clay being from a different source). So, later, when we class the pottery, we'll be looking for any 'slip', as a style. Paint: I always wondered where they bought the paint. And I wasn't wrong! Trading among native-americans often involved special minerals for the paint. Few colors were available to early potters: - White: very pure clay, free from iron, similar to a white slip. - Black organic: certain weeds like tansy mustard and bee weed, can be boiled down to create a gummy black mass. - Black mineral: by mixing plant juice with a type of iron-oxide, a liquid paint is achieved - Black on red-clay: difficult, since the red clay also contained iron. They switched to a manganese, though the source is unknown. - Red/brown: likely from yellow limonite, which oxidizes on firing to a red or brown color. Hematite does not make a permanent red paint, since it tends to rub off. - Fugitive red: This is a hematite, mixed with a plant juice and painted on AFTER firing. Usually it's painted over gray pottery. Glaze paint: Some tribes used a glaze of silica with a fusible base, such as lead, copper, or calcium oxide. They were always used for design, and never as a slip (which you wouldn't expect). The reason was that their technique tended to produce a melted/runny glaze, producing a messy design (mainly found in the White Mountains). Firing: There's more?! This is interesting, darn it! There's no evidence of early kilns, so the method is probably similar to that described above (piling fuel around the pottery and burning it). In understanding the coloration of sherds, chemistry is important (sigh). In gray pottery, the iron combines with oxygen to create a 'ferrous' condition (FeO). With cream, buff, orange, brown and red pottery, it's a 'ferric' condition (Fe2O3). And lastly (whew), most ancient potteriess were fired in an 'oxidizing atmosphere'. Only during the last stage of firing, if the pot is protected, can a 'reducing atmosphere' be achieved with a buff coloration. This comes into play later with classification. |
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Pottery Classification Questions OK, this is the fun part! Here's the basic steps, when you pick up a pottery sherd. The next page has a step-by-step classifier. (1) COLOR: - Gray (cream/buff): either oxidizing or reducing atmosphere (low iron content). Clay would have come from sedimentary or alluvial sources where the iron was likely leached out. - Orange, red or brown: likely came from a residual source. Red means higher iron and little carbon. Brown means higher levels of carbon, possibly from an old lava flow with old roots. - Black: either a very high iron content, or from use in cooking (carbonized) (2) SMUDGING: This is a shiny black on the interior of the bowl, and is achieved after firing and still red-hot, by inverting the bowl into a bed of juniper bark, while protecting the exterior side. The incomplete combustion leaves a layer of carbon on the surface. Sherd found in the mountain areas often have this characteristic. (3) SURFACE TREATMENT: - Coils visible? - Slip used? (again, this is a differing cream clay applied to the exterior of other clay). Usually red or white. - Skum surface? This is mainly in western AZ, where alkali salts were likely used to moisten the exterior surface. It appears as a almost a glaze. - Applique surface? Were additional designs added to the exterior surface (which tended to break off). - Tooling? Here the clay is incised by punching or scraping. The shape was important. - Engraving? After firing, a design is sometimes etched into the painted areas. - Surface texture? Choices are polished/not, smooth, rough or granular? (4) PAINT - Organic or mineral? Organic paints penetrate the surface of the clay. The edge of a painted line will appear fuzzy with a 10x glass. Mineral paints tend to be more sharp. (5) DECORATION Since we're looking at a sherd, this is not too defining. But small repeated lines often give you a clue. (6) THE CORE If you have a recent crack, you can look for at the type of clay, its temper (sand pebble size/shape), and possibly a slip (outer clay). Sometimes you'll find a core of gray/black with the exterior a warm color. Tsegi Orange and Sunset Red are good examples, and are achieved through a specialized firing to differ the external from the internal effects. (7) THE DESIGN You may not have much to look at with a sherd. But here's the more common types: - Lino style: crude lines and dots. - Kana-a style: triangles and fine parallel lines that don't meet accurately. - Black Mesa style: broad lines, large triangles, often with pendent dots. - Sosi style: broad lines and large barbed lines, bold. - Dogoszhi style: diagonal hatching in panals. - Flagstaff style: variations of barbed lines, with mini-Sosi elements. - Kayenta style: dark masses, underlain by crossed/netted lines at right angles. - Tularosa style: massed black areas, with cross-hatched areas between. |
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Pottery Classing Guide On the next page, is a basic guide for classing a pottery sherd. First, it comes from Harold Colton in 1937, so if you're an expert, calm down! We provide it here for two reasons: (1) It's easy to follow, (2) It's historical and fun to apply. That's what we're here for! Plus, the Sedona and Flagstaff library copies of his book are getting worn out. GUIDE TO CLASSIFYING NORTHERN ARIZONA POTTERY SHERDS |
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