Ceramics

Characteristics of a culture can be derived from a variety of sources. Ceramics, in particular, can describe a culture in terms of the sophistication of its technologies, evidence of trade between and among ancient cultures, and insights derived from designs or associated iconography. It is logical then that ceramic artifacts be given critical scrutiny if researchers hope to divine all the information possible about their makers. Radiography, endoscopy, and advanced imaging modalities can all bring unique data regarding ceramics to bear on the understanding of ancient cultures.

Radiography

When imaging ceramics, their construction characteristics are the key to determining exposure factors, primarily kVp. In order to get a usable image, the type of material and the density variations within the piece need to be considered. For conventional radiographic film, typically, the necessary penetrating "power" will range from 60 to 80 kVp. If a digital image receptor will be used, the range should be increased from 80 to 100 kVp. Several approaches can be used to gather as much data as possible. Borrowing from the field of photography, it is helpful to "bracket" the images by using at least three different mAs, exposure settings. The first exposure would be with the kVp and mAs settings that would be predicted to produce the most satisfactory image. Without changing the kVp setting, the second exposure would be made with half the mAs used for the first exposure. The third image would be made with the same kVp as the two previous values, but with double the mAs value used on the first exposure. This will ensure that the varied densities are all captured on the image and will help determine the "best" exposure settings for that particular object. When using standard radiography, once the image is produced, more is on the film than can be detected by the human eye. Scanning the image on a flatbed scanner with a transparency adapter at high resolution—at least 300 dots per inch (dpi)—transfers the data from the film into a digital format. The digital image can then be postprocessed by manipulating such variables as contrast and brightness in computerized photo-mastering programs such as Adobe Photoshop®. In this manner, what wasn't initially seen can now be visualized.

When imaging ceramics, there are several advantages to using an industrial computed radiography (CR) system. Although there is a specific algorithm for ceramic, the initial image should be satisfactory. In addition, because postprocessing manipulation can be performed within the CR system, there is no need for exposure bracketing or scanning an imaging into a photo-mastering program.

Some ceramics are complex in their structure or are designed for a specific function. Examples of complex ceramics would be stirrup pots and whistle pots. As with other artifacts or human remains, once the initial two-view survey x-rays have been taken and analyzed, additional views may be required to fully demonstrate the more complex structures. If possible, all conventional radiographic exposures should be carried out with a nonscreen imaging method. The initial two radiographs may be termed lateral and anterior-posterior

Figure 8.1A A ceramic from the north coast of Peru positioned for a lateral radiograph. Note the placement of the foam wedges to achieve the position.

(AP), although the characteristic structures found on humans for that designation are not present. For convenience, if the ceramic has a handle or handles, the lateral view may be considered the view where the handle is parallel to the film (Figures 8.1A and 8.1B). For the second projection, the AP, the ceramic or x-ray source and image receptor would be rotated 90° (Figure 8.2). If possible, the ceramic piece can be placed on a "turntable" to facilitate rotation. With this second projection, if the ceramic has two handles, they would

Figure 8.1B The radiograph of the ceramic vessel in the lateral position.
Figure 8.2 The AP projection of the ceramic.

be superimposed. The handle closest to the image receptor would appear less magnified than the handle closer to the x-ray source.

If the ceramic held liquid or other materials, the radiograph can yield information about the burial position of the piece. The residual material will form a level parallel to the dependent portion as influenced by gravity (Figure 8.3).

The two views described should be considered an absolute minimum. The additional views required will be dictated by the object being studied and may require more creative projection angles. Most commonly, a view will be required to document the base of the ceramic. If the opening, or mouth, is larger than the base, the procedure can be accomplished by placing the piece on top of the image receptor and positioning the x-ray source above the ceramic. The x-ray source-to-image receptor distance (SID) should be the same for all projections. A change in the SID would require an adjustment to the mAs value. Recall the implications of the direct square law presented in Section I, Chapter 2. If the opening of the ceramic is smaller than the base, the described view would provide information regarding the base; however, the top will be superimposed over the base. This can be overcome by utilizing the principle of magnification. Bringing the x-ray source as close to the top as possible would magnify the top. If the sides of the ceramic are high enough, this maneuver should cause the top to be projected outside the shadow of the base.

Figure 8.3 AP radiograph of ceramic pot of the chiribaya culture. Note the position of the internal residual material referenced to gravity, which indicates the burial position of the ceramic.

Another common additional view is termed oblique. With this projection, the x-ray beam is directed at some angle across the object under investigation. The exact angle will be determined by the specific region of interest, but remember that the greater the angle, the more distortion will be evident on the processed image. An oblique projection may be employed to document the manner in which the base or handles are fixed to the sides of the object (Figure 8.4).

Endoscopy

Ceramics typically offer ample access routes for endoscope introduction (Figure 8.5). Clearly, there are many ceramic pieces that are wide-mouthed, making direct observation possible without the assistance of an endoscope. However, the endoscope may be utilized to provide macro or close-up views of the inner surface of the wide-mouthed ceramic pieces in order to examine the fine details of ceramic production. In cases where the ceramic is structured in a fashion in which only small openings are present and direct visualization is not possible, the endoscope can assist in the data collection of the internal construction features of the object.

Similar to the examination of other artifacts or human remains, care must be taken not to damage the artifact with the endoscope insertion. A protective sheath guide can be

Figure 8.4 oblique radiograph of a ceramic pot allowing better visualization of handle attachments.
Figure 8.5 Endoscopic entry route into a ceramic pot through the top.

Figure 8.6 (See color insert following page 12.) Two internal endoscopic images of a ceramic pot showing a far-focus view (left) and near-focus view (right).

placed prior to introduction of the endoscope to avoid any scraping that might occur at the point of entry. A preliminary survey of the internal environment is conducted in order to determine if there are any low-density remnants or objects within the ceramic piece not demonstrated by radiograph. The instrumentation selection is critical in this initial survey. In large, deep ceramics, a far-focus lens would better assess the overall structure, whereas a near-focus lens would be more beneficial in a smaller ceramic. If the construction features are such that many interior angles have been produced, a right angle lens can be employed to allow improved visualization. Figure 8.6 presents endoscopic examples of a near-focus lens image and then a far-focus lens image of the same ceramic. Additionally, a stereo lens will allow for the measurement of objects within the ceramic, fissures, or construction features of interest. Endoscope diameter and length are also important considerations in instrument selection to match the task. In this manner, the internal environment of the ceramic, which may help describe the sophistication of ancient technologies, can be mapped and documented.

Next, any target structures or objects identified by x-ray within the ceramic can be inspected and documented. Ceramics designed to carry out a specific function often have structures within structures to allow functionality. The endoscope may be able to be manipulated to view these features. Typically, the near-focus lens would be the lens of choice for this application (Figure 8.7).

Finally, in accordance with the specific research goals and protocols, removal of an object from within the ceramic can be facilitated under endoscopic guidance. Samples of contents and scrapings can also be conducted under direct endoscopic visualization, documenting that researchers are actually collecting what they believe they are collecting.

The endoscope image may also help determine what the ceramic was used for. For example, some ceramics were used to supply food for the associated mummy, whereas other ceramics were used to hold liquids for the mummy to use in the afterlife. Figure 8.8 is an endoscopic image from within a small Chiribaya ceramic associated with a child mummy. The image demonstrates the fluid level at the time of burial as well as the residual material of that fluid. The fluid was identified by the residual material as being corn typically used to make chicha, a fermented drink similar to modern beer.

Figure 8.7 (See color insert following page 12.) Endoscopic images of objects held within a ceramic pot.

In each phase of the endoscopic ceramic inspection procedure; survey, target analysis, and sample collection or object retrieval—radiographs documenting position are crucial to understanding and interpreting the data collected. In the human body, there are usually some anatomical landmarks, such as bony structures, which help the endoscopist

Figure 8.8 (see color insert following page 12.) Endoscopic image of linear discoloration left by a fluid level (arrow). The ceramic was likely to have held a form of chicha.

understand where in that body the endoscope is and what is likely to appear in its field of view. These internal anatomical landmarks do not exist in the internal environment of a ceramic object, making it difficult to know where the viewing lens of the scope is actually located. This is particularly the case in complex ceramic structures. For example, in a quadruple gourd stirrup pot, endoscope position can be disorienting, leaving the researcher to question in what side and where within that side the endoscope actually is. A radiograph or radiographs can quickly clarify any confusion as to precise location of the endoscope, and therefore, what is actually in its field of view.

Radiography and endoscopy can both provide complementary information regarding the condition of ceramics. In a South American ceramic at the Yale Peabody Museum in New Haven, Connecticut, a radiograph demonstrated that repair work had been done sometime in the past (Figure 8.9). A crack in the ceramic was also seen on the radiograph. The endoscope was able to examine the crack and record an image for the museum (Figure 8.10).

Advanced imaging

Advanced imaging such as CT is a valuable tool in understanding the spatial relationships among the substructures of a ceramic artifact. Often, ceramics, such as whistle pots, hold structures within structures, making the application of CT scans a valuable tool. However, most CT scanners are designed to image living human bodies, so the preset protocols offer a challenge to the technologist operating the equipment. Industrial scanners often yield more satisfactory results.

In the case of ceramics, transportation is often more feasible as intact ceramic objects can be more easily stabilized for moving. However, as with all advanced imaging, the decision to scan must be informed by discussions of the safety of the object, and by what

Figure 8.9 Radiograph documenting the location of the endoscope as it explores the internal features of a ceramic. The radiograph revealed repair efforts as well as a crack (arrows).
Figure 8.10 Endoscopic image of crack in the internal wall of the ceramic seen initially on x-ray.

additional data will be obtained. Also, what will be done with the data is a critical question. Often, CT scanning of a ceramic artifact is conducted to produce three-dimensional (3D) images for museum displays. Although this is an appropriate application of the technology, the research protocol should include an "imaging for display" aspect to warrant CT scanning.

Ceramics Case study: The Whistle Pot

To demonstrate the field application of paleoimaging related to the imaging of complex ceramic objects, we present the following case.

An Inca whistle pot was found within the ruins of Tucume, near Chiclayo, Peru. Radiographs from various projections demonstrate the overall construction features of this specialized ceramic. The endoscope was passed into the ceramic and manipulated into position allowing visualization of the whistle mechanism within the ceramic, the structure within the structure (Figure 8.11). A radiograph documented the position of the endoscope within the pot. The data can now be incorporated into our understanding of how these specific function ceramics were made and inferences regarding the sophistication of the technology can be drawn (Incas Unwrapped 2001a).

Figure 8.11 (See color insert following page 12.) Endoscopic images of the whistle mechanism within the whistle pot pictured at the top.

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