Long-lasting pigment fixation of ancient paintings using hydrophilic microgels prepared from hydroxyethyl cellulose and sodium alginate.

The long-term fixation of mineral pigments in ancient paintings has always been a challenge. Gelatin alum solution (GAW), as a traditional pigment fixative, presents good pigment fixation in the early stage of use, but its poor durability is well known. In this work, a microgel (SH1:1) prepared from sodium alginate and hydroxyethyl cellulose was proposed to replace GAW for the pigment fixation due to its micro scale, strong adhesion, and good chemical stability. The evaluation results indicate that SH1:1 microgel can endow the treated unstable pigment samples with better fixation effect and durability. Especially after 10 days of temperature humidity alternating aging, the SH1:1 treated samples show smaller morphological changes and higher retention rates of tensile strength and folding endurance (98.5 % and 79.2 %) than those of GAW treatment (96.5 % and 46.5 %). The excellent fixation effect is attributed to SH1:1 microgel's strong bonding strength to mineral pigments and paper fibers. Moreover, the outstanding durability is due to the good aging resistance, water retention and mild alkalinity (pH = 7.0-7.5) conferred by SH1:1 treatment, preventing rapid failure of fixative, as well as preventing paper acidification and degradation. Therefore, SH1:1 microgel has great application potential in restoring antique paintings.