A preliminary study of using greener materials including deep eutectic solvents (DESs) for the cleaning of silver tarnish

• Employment of deep eutectic solvents as greener materials for silver cleaning. • Obstinate silver tarnish successfully transformed into more soluble products. • Controllable cleaning process and suitable for objects with curved surfaces. We present a preliminary study of the cleaning of artificially tarnished silver mock-ups with several greener materials, including sodium glycinate, ethylenediamine-N,N’-disuccinic acid (EDDS), saponin, and deep eutectic solvents (DESs), in comparison to a commercial silver polish product. While sodium glycinate, EDDS and saponin did not show substantial cleaning effects on light silver tarnish, a two-step method combining (i) oxidative DESs and (ii) sodium glycinate-based suspension proved effective for the removal of heavy tarnish. However, observations via colorimetry, interferometry microscopy, optical microscopy, and scanning electron microscopy showed that this two-step method could lead to surface roughening. While clear scratches and over-polishing issues were observed on coupon surfaces cleaned by the commercial silver polish product, the use of a slurry composed of sodium glycinate, citric acid, glycerol and water resulted in optimal cleaning effects, despite its relatively low cleaning rate.