CO2 Snow Cleaning of Red Clay and Starch Deposits on Natural Fibre Textiles: Multi-Analytical Material Response Profiles

The response of a textile to CO2 snow cleaning depends on both the nature of the deposit and the structure of the fabric, and its assessment must consider deposit removal together with alteration of the substrate. In this exploratory study, six model systems were prepared by combining three natural fibre textiles (silk, cotton and linen) with a particulate red clay deposit and a gelatinised wheat starch film. Eighteen specimens were characterised before deposit application (M0), after application and drying (M1) and after CO2 snow treatment (M2), performed using predefined configurations ranging from 1.5 to 6 bar and from 1 to 4 min. Optical measurements followed each specimen through the three states, complemented by surface pH and wettability. In parallel, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) provided local spectral characterisation at selected contact sites, while digital and field-emission scanning electron microscopy supplied complementary morphological evidence at different observation scales. The two deposits behaved differently. In the red clay systems, colour recovered partially, with residual colour differences (ΔE*ab) of 6.65 to 34.00 and a persistent reddish and yellowish shift. In the starch systems, low chromatic contrast limited the specificity of colour measurements, while gloss, wetting and microscopy provided complementary evidence. Post-treatment gloss at 85° was below the clean value in 16 of the 18 specimens. Selected FESEM fields showed separated silk filaments and broken cotton fibre ends. These observations identify potential conservation concerns, but their origin and prevalence cannot be established from the available controls and sampling. The results provide exploratory evidence for further evaluation of deposit reduction and textile preservation.