The discoloration problem has a well-understood chemical origin. Waterlogged archaeological wood, abbreviated WAW in the literature, has spent centuries in oxygen-poor environments where microbial decay preferentially consumed cellulose and hemicellulose, leaving behind a lignin-rich scaffold. Once this material is excavated and handled in air, the residual lignin undergoes progressive oxidation. That oxidation generates quinones and other conjugated chromophores, molecular structures whose extended systems of alternating double bonds absorb visible light and impart the severe darkening conservators observe. Because these chromophores are embedded in a decayed, structurally compromised matrix, removing them without causing further damage is a delicate balancing act.

Conventional reductive bleaching agents have long been the standard response, but each comes with trade-offs. Sodium dithionite, a powerful reductant, works well in alkaline conditions that can be harsh on degraded wood fibers. Sodium borohydride delivers strong reducing power but evolves hydrogen gas as it reacts, raising safety and compatibility concerns in conservation laboratories and requiring careful buffering to keep pH in check. The research team, led by Shuangtong Wu of Peking University’s School of Archaeology and Museology together with Yiding Liu, Jiahang Song, and corresponding author Kai Wang, sought a formulation that could deliver effective decolorization while remaining operationally gentle, without demanding elaborate pH control or generating hazardous byproducts.

Their solution pairs thiourea dioxide, known in chemistry as TDO, with amine boranes, a class of compounds in which boron is bonded to nitrogen in an amine backbone. The researchers evaluated two amine boranes specifically: dimethylamine borane, or DMAB, and tert-butylamine borane, or TBAB. Each component brings distinct reductive chemistry to the mixture. Thiourea dioxide is a sulfinic acid derivative that releases reducing sulfoxylate species under mild conditions, while amine boranes deliver hydrogen in a controlled, boron-mediated reduction pathway. The hypothesis was that combining them would generate reductive species in a complementary fashion, attacking the quinone chromophores through multiple routes simultaneously rather than relying on a single reaction mechanism.

A key methodological contribution of the study lies in its quantitative evaluation strategy. Assessing bleaching performance on real archaeological samples is complicated by the heterogeneity of the material: every artifact differs in wood species, decay history, and chromophore content, making comparisons between treatments statistically fragile. To overcome this, the team constructed a paper-based solid-phase model containing a covalently linked ortho-quinone motif, a synthetic stand-in that mimics the specific chromophores responsible for discoloration in WAW. By anchoring the target chromophore to a solid substrate, the researchers could measure decolorization ratios reproducibly across treatment conditions, isolating the chemistry from the variability of genuine artifacts.

Using this model system alongside actual waterlogged archaeological wood samples, the team tested thiourea dioxide alone, DMAB alone, TBAB alone, and their pairwise combinations. The results were consistent: the composite formulations outperformed every single-component treatment in both the magnitude and the rate of decolorization. This synergy is the study’s central finding. Rather than simply adding the effects of two mediocre reductants, the combination appears to unlock reductive pathways that neither agent accesses efficiently on its own, with the two chemicals generating complementary reductive species that converge on the conjugated chromophores from different mechanistic directions.

The optimal formulation identified in the study combined 0.025 molar thiourea dioxide with 0.025 molar dimethylamine borane, an equimolar pairing at modest concentrations. Applied to hardwood samples, this blend achieved a decolorization ratio of 31.6 percent, while softwood samples reached 23.2 percent. Notably, the treatment maintained near-neutral pH throughout the process without any added buffer, addressing one of the most persistent operational complaints about conventional reductive bleaching in conservation practice. For waterlogged wood, whose decayed structure is acutely sensitive to pH swings, that compatibility is not a cosmetic advantage but a fundamental requirement for any treatment that might see real-world adoption.

The distinction between hardwood and softwood performance reflects the underlying chemistry of the two wood types. Hardwoods, from angiosperm trees, and softwoods, from gymnosperms, differ substantially in lignin composition and structure, and the quinone-type chromophores generated by oxidation differ accordingly. The higher decolorization ratio on hardwood suggests that the TDO–DMAB system attacks the hardwood-derived chromophores more efficiently, though the softwood result of 23.2 percent still represents a meaningful improvement over single-component treatments. For conservators, the practical implication is that treatment protocols may need to account for wood type when selecting formulations and predicting outcomes.

The work, published on 19 October 2026 as an open-access article in npj Heritage Science, was supported by the Archaeological Talent Promotion Program of China and the Independent Scientific Research Innovation Funding Project of the National Centre for Archaeology. The authors declare no competing interests. Because the article was shared early to provide faster access to peer-reviewed, accepted research, the published version remains subject to further editorial refinement, though it carries a permanent DOI and is fully citable.

For the conservation field, the significance of the study extends beyond the specific numbers. It demonstrates a rational framework for designing reductive treatments around synergy rather than brute reducing power, and it introduces a quantitative model substrate that other laboratories can adopt for benchmarking. Waterlogged archaeological wood represents one of the most abundant and vulnerable categories of organic heritage, encompassing everything from Neolithic lake dwellings to medieval shipwrecks, and every improvement in its treatment chemistry translates directly into more artifacts preserved for study and display. Whether the TDO–amine borane system will scale from laboratory samples to full conservation workflows remains the next question, but the study provides both the chemical rationale and the evaluation tools to guide that transition.

Subject of Research: Chemical decolorization treatment for waterlogged archaeological wood using a synergistic thiourea dioxide and amine borane reducing system

Article Title: Synergistic reductive decolorization of waterlogged archaeological wood via a thiourea dioxide–amine borane system

Article References: Wu, S., Liu, Y., Song, J., & Wang, K. (2026). Synergistic reductive decolorization of waterlogged archaeological wood via a thiourea dioxide–amine borane system. npj Heritage Science. https://doi.org/10.1038/s40494-026-03058-6

Image Credits: AI Generated

DOI: 10.1038/s40494-026-03058-6

Keywords: waterlogged archaeological wood, thiourea dioxide, amine borane, decolorization, wood conservation, lignin oxidation, quinones, reductive bleaching, heritage science, dimethylamine borane, chromophores, archaeological chemistry