A preliminary study on a phosphotungstic acid-barium hydroxide system preventing lead white blackening in Xuan paper-based paintings

Lead white blackening is a common deterioration in traditional Chinese paintings that severely undermines their artistic and cultural value. This study proposes a two-step preventive treatment involving sequential application of phosphotungstic acid-phosphoric acid-acetone (PPA) and barium hydroxide-ethyl cellulose-methanol (BCM) solutions. Accelerated H₂S aging tests showed that the treated lead white only exhibited localized blackening after 20 days of aging, whereas the untreated control turned completely black within 1 day. Comprehensive characterizations (EDS, SEM, XRD, XPS, FTIR) demonstrated that phosphotungstic acid chelates Pb(II) to inhibit H₂S-induced blackening, while barium hydroxide neutralizes residual acid and forms a protective barrier. Mechanical tests confirmed no adverse impact on paper substrates. This method offers a promising reference for lead white blackening prevention, though its on-site applicability and long-term stability require further validation.