Terahertz time-domain imaging for the examination of gilded wooden artifacts

Abstract

Terahertz imaging is unlocking unique capabilities for the analysis of cultural heritage artifacts. This paper uses terahertz time-domain imaging for the study of a gilded wooden artifact, providing a means to perform stratigraphic analysis, yielding information about the composition of the artifact, presence of certain materials identifiable through their THz spectral fingerprint, as well as alterations that have been performed over time. Due to the limited information that is available for many historic artifacts, the data that can be obtained through the presented technique can guide proper stewardship of the artifact, informing its long-term preservation.

Figure 1

Our Lady of Kazan from unknown artist. (a) Upper profile. (b) Front view. (c) Bottom profile. (d) Peak-to-peak image.

Figure 2

(a) 3D Time-of-flight. (b) 2D Time-of-Flight. (c) B-scan along the y-axis indicated as solid line in the 2D ToF. (d) B-scan along the x-axis indicated as dashed line in the 2D ToF. Arrows in B-scans correspond to painted areas where THz radiation penetrates into inner layers on the artwork.

Figure 3

(a, b) Deconvolved and normalized B-scans. The red line in the insets indicate where the B-scans were measured. (c, d) Processed waveforms corresponding to pixels 251 and 264, from (a) and (b) B-scans, respectively, indicated as dashed lines. Interface labeled as I2 is only present in areas corresponding to faces and necks, as shown by the B-scans in the zones indicated by the red arrows. These additional interface can clearly be seen next to the first echo, corresponding to the surface of the icon.

Figure 4

(a) Mercury sulfide detected in the painting, indicated by red pixels; six zones were clearly identified. Blue pixels correspond to spectra were vermilion possibly be present. Inset shows the XRF emission spectrum taken from the green circle. (b) Photographs corresponding to zones 1–6, where mercury sulfide was detected. (c–e) Spectra of waveforms from the six zones. The characteristic absorption peak of mercury sulfide can be clearly seen at 1.14 THz.

Figure 5

API-Teragauge system with photoconductive transceiver head for measurements in reflection geometry.