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Micro-CT Examination of Wooden and Metal Jewelry

Figure 1: Decorative beads imaged in this study

Precious artifacts and historical art objects are often affected by decay, environmental pollution, vandalism, or just simple age and neglect. Micro-CT is well suited to analyze historical artifacts for restoration and preservation, allowing conservators to inspect the exterior surfaces and interior structures without destroying the original objects. Unlike ordinary 2D radiography, which is primarily useful for studying metal objects, micro-CT scanning has successfully been used to image objects made from organics, ceramics, and glass in addition to metal.

Micro-CT is being employed in increasingly imaginative ways to help to protect and preserve art and artifacts worldwide. For example, conservators are developing techniques to virtually unwrap and digitally flatten papyrus scrolls in order to create geometric models of the scrolls and their surface textures. There are studies using micro-CT to investigate objects contained within soil blocks lifted from a medieval cemetery, providing actual views of the objects and where they are located within the blocks. Natural history museums have employed micro-CT scanning to create 3D images of fragile specimens in order to produce physical models with 3D printing, making these specimens more accessible.

For our study this month, we utilized our SkyScan 1275 high speed desktop micro-CT to quickly examine a wooden and a metallic jewelry bead. Each scan took less than 25 minutes.

Micro-CT Scan of Jewelry Beads

Our micro-CT examination of these jewelry beads allows us to compare the structure of both a metal and organic component of a decorative necklace. As can be seen in Figure 1 above, both the metallic and wooden beads are comprised of either multiple materials or detailed surface texture.

Figure 2: Two-dimensional slices through the wooden bead

As can be seen in Figure 2 and Figure 3, the wooden bead appears to have been manufactured from approximately three different types of wood. This tracks well visually with what we observe based on the coloration of the layers seen in the physical sample. The middle layer and both edges all appear, based on color as well as pore size and distribution, to be consistent with one another. The other layers show similar patterns with consistent X-ray attenuation and pore morphology.

Figure 3: Clipped volumetric rendering of a decorative wooden bead

While the metallic bead is less informative since it is simply a metal shell without internal structure, we can see the detailed surface structures as shown in Figure 4.

Figure 4: Two-dimensional slices through the metallic bead

As shown in Figure 5, the details of the surface are well captured both on the internal and external faces of the thin walled shell used to form the metallic bead. In comparison to the wooden bead, there is no cord visible running through the center of this bead. While the cord is still physical present (as seen in Figure 1), the cord is not visible in the current rendering due to the high difference in X-ray attenuation between metal and organic components such as the cord. We know that X-ray energy attenuates exponentially with atomic number, so the difference in attenuation between lighter organic molecules and common metals is indeed quite large. Since the lighter, organic elements are closer to air than to the metals in X-ray adsorption, they often do not show up when looking at images optimized to show metallic samples.

Figure 5: Clipped volumetric rendering of a metallic bead

Conclusion

Micro-CT is particularly useful in non-destructive examination of the internal structures of fragile or rare samples such as are encountered in the art community. We hope you found this Image of the Month informative. If you have an Image of the Month sample that you would like us to scan, please contact us by calling Seth Hogg at 610-366-7103 or e-mailing seth.hogg@microphotonics.com

Scan Specifications

Sample Wooden Bead Metallic Bead
Voltage (kV) 50 80
Current (µA) 200 125
Pixel Size (µm) 25 25
Rotation Step 0.4 0.4
Scan Time (HH:MM:SS) 00:23:26 00:22:23

This scan was completed on our high speed desktop SkyScan 1275 system at the Micro Photonics Imaging Laboratory in Allentown, PA. Reconstructions were completed using NRecon and visualization of 2D and 3D results were completed using DataViewer and CTVox.

 

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