Systematic Evaluation of Washing Time in a Mild SLES‑Based Protocol for the Conservation of Madder‑Dyed Historical Cotton Textiles

This study aimed to evaluate the washing time within a mild cleaning protocol for historical textiles dyed with madder, using sodium lauryl ether sulfate (SLES) as the surfactant. Madder-dyed cotton fabrics, soiled and aged via a hygrothermal process, were washed in a solution containing SLES, ethylenediaminetetraacetic acid as a builder, and sodium carboxymethyl cellulose as a soil-suspending agent. Washing was performed at time intervals ranging from 15 to 90 minutes, followed by three rinsing stages. The effects of the washing process were evaluated after an accelerated aging period using colorimetry, pH analysis, visible spectrophotometry, DRIFT spectroscopy, and tensile strength testing. The findings indicate that a 60-minute washing time represents the recommended balance between effective soil removal and minimal damage. Shorter washing times (15 minutes) resulted in incomplete soil removal, while longer times (75 and 90 minutes) led to significant dye extraction and a destructive pH drop to approximately 4 after aging, attributed to residual SLES. DRIFT analysis and tensile testing did not reveal significant structural or mechanical degradation during washing or after aging. The findings suggest that a 60-minute washing period within this SLES-based protocol, followed by three rinsing stages, provides a safe and effective cleaning approach for this type of historical textile.