Table 2 List of cleaning solutions and delivery systems evaluated on mock-ups and discreet areas of Whaam!, with preparation, application and clearance strategies

Aqueous solvents

Deionised water; buffered waters with a pH range of 5.5–6.5

Buffered waters made with citric acid, -(N-morpholino) ethane sulfonic acid (MES) and sodium hydroxide accordingly to The Modular Cleaning Program^a

Applied with hand-rolled cotton swabs rolled over the paint surface up to 10 times, to cover an area of approximately 1 cm²

Deionised water (pH 5.5, conductivity 4 µS/cm) = DI water

Non-polar solvents

Shellsol D40 [Ben-Day dots mock-up only]; cyclic silicone decamethylcyclopentasiloxane (D5)

Not required

As above

Not required

Aqueous-based solutions

Tri-ammonium citrate (TAC); non-ionic surfactants ECOSURF™ EH-6, ECOSURF™ EH-9, BIO-SOFT^® BS1 and BS2

Aqueous-based solutions were prepared by weight with DI water. The concentration of the TAC ranged from 0.5 to 2% w/w; solutions containing non-ionic surfactants had a concentration of 0.5–1% w/w

As above

Deionised water (pH 5.5, conductivity 4 µS/cm) = DI water

Polysaccharide-based gel [rigid]

Agarose (3% w/w)

Gellan gum (3% w/w)

Disperse the polysaccharide powder in deionised water, heat the solution at ~ 95 °C under stirring. The hot solutions were then poured into a flat container of the desired thickness and allow to cool (and gel) at room temperature

Cast gels cut in to small pieces (~ 1.5 × 1.5 cm). Before application, excess water was blotted onto Whatman filter paper, and left in contact with the mock-ups surface initially for 1 min

Not required as used as hydrogel only

Excess water released onto surface removed using a dry cotton swab

Silicone emulsifiers [spreadable]

Velvesil Plus; Shin-Etsu KSG 210; Shin-Etsu KSG 350z—aqueous phase 20% w/w

Prepared with 60% w/w silicone emulsifier, then thinned with D5 solvent (to 80% w/w), with an aqueous phase content of 20% w/w—either deionised water or with added chelators and/or surfactants. The aqueous phase was dispersed through the diluted emulsifier drop by drop and stirred vigorously to create the emulsion^b

Applied by a soft brush, creating a uniform layer over the surface, and left in place for 1 min

Dry cotton swab first (to remove the majority of emulsifier) and D5 silicone solvent-dipped swabs rolled onto the surface until visible residues were not detected (average 3–4 applications)

Nanorestore Gel^® hydrogels or loaded with an aqueous-based solution [flexible]

Nanorestore Gel^® Extra Dry (now MWR)

Nanorestore Gel^® Peggy 5

Nanorestore Gel^® Peggy 6—aqueous content ~ 90%

Gels dispatched ready for use as sheets (~10 × 15 cm), immersed in a small volume of demineralised water; rinsed by immersion in DI water for 24 h before use^c

After rinsing gels were pre-loaded with the cleaning solutions by immersion for 12 h

Blotted using Whatman filter paper; 1.5 × 1.5 cm gel pieces were placed on mock-ups for 1 min; light finger pressure was applied to optimise adhesion and to remove any air bubbles formed. The gels were gently peeled away from the surface, with no mechanical action required

Not required for pure hydrogels. When uploaded with active agents, clearance involved the application of corresponding Nanorestore Gel^® hydrogels for the same period. The gels can transfer a thin layer of liquid on to the surface, which can be removed by blotting the gel well before application; equally the paint surface can be lightly blotted after application if appropriate