Digital Archiving Preserves Han Dynasty Slips
Buried for millennia in the extreme aridity of Northwest China’s Gobi environment, more than 500 ancient bamboo and wooden slips known as jiandu are undergoing panoramic digital archiving via a 32-channel multispectral imaging system.
The artifacts, dating back to the Han Dynasty between 206 BC and AD 220, were primarily unearthed from frontier fortress sites. Crafted largely from poplar, rose willow, and pine, these organic substrates are roughly 2,000 years old. With the naked eye, researchers face near-total visual obscurity. Surface degradation—including salt efflorescence, insect damage, mildew stains, and transverse cracks—actively obscures the brush-and-ink records written before the widespread adoption of paper.
Gansu Jiandu Museum initially deployed near-infrared imaging to penetrate this degradation. Dorje Rinchen, a staff member in the museum’s science and technology conservation department, explained that infrared wavelengths are strongly absorbed by ink while remaining weakly absorbed by the organic wooden and bamboo matrices. This single-band approach revived faint text outlines, but left comprehensive structural logging incomplete.
Single-band limitations prompted the institution to introduce an advanced multispectral imaging system in 2025. Developed by Tianjin Hengda Wenbo Technology, the hardware integrates high-sensitivity sensors capable of capturing data across 32 distinct wavelengths, spanning from near-ultraviolet to near-infrared spectra.
Multispectral Imaging Reveals Hidden Artifact Details
By unfolding the physical slips across the spectral dimension, the equipment records 33 individual frames per artifact, including the standard visual capture. Du Peng, deputy general manager at Tianjin Hengda Wenbo Technology, noted that optical penetration and reflection vary depending on the specific wavelength deployed against stains and degradation.
When switching to the near-ultraviolet band, salt efflorescence and subtle surface cracks—invisible under ambient white light—step into sharp relief. By comparing variations across all 32 bands, conservationists isolate original ink from subsequent environmental contamination. This differential analysis maps the exact physical footprint of insect borings and chemical salt deposits.
The system effectively compiles a comprehensive diagnostic file for every organic relic. Because jiandu are nonrenewable organic materials experiencing slow, natural decomposition, these multi-wavelength scans function as chronological medical charts. Periodic re-scanning allows the conservation team to track structural decay rates.
Cross-Platform Applications Beyond Frontier Slips
The underlying optical architecture is not restricted to dry-land wooden records. Du Peng stated that the multispectral imaging apparatus scales directly to other degraded organic mediums. These include historical calligraphy, paintings, and artifacts, alongside delicate grotto and tomb murals.
The developer anticipates that standardizing these 32-band capture workflows will deliver foundational data support for institutional archiving, extraction of hidden information, and virtual restoration pipelines. As Gansu Jiandu Museum continues holding bamboo and wooden slips dating back to the Han Dynasty, the use of a multispectral imaging system helps document and protect the slips.
