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

Aqueous solvents

Deionised water (DI); adjusted water 6:6; buffered waters (pH range 5.5–6.5)

Adjusted water prepared with ammonium hydroxide and acetic acid, buffered waters with citric acid, 2-(N-morpholino)ethane sulfonic acid (MES) and sodium hydroxide, accordingly to The Modular Cleaning Program^a

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

Adjusted water 6:6-dipped swabs, rolled on average for 3 applications (for areas tested with buffered waters only)

Preliminary tests on mock-up samples, followed by trials on Addendum; assessed by visual observations for changes to the surface (e.g. swelling and surface appearance)

Non-polar solvents

Cyclic silicone: decamethylcyclopentasiloxane (D5)

Hydrocarbons: Shellsol^®D40, Shellsol^®A, Stoddard.

Not required

As above

Not required

Preliminary tests on mock-up samples, followed by visual observations and digital microscopy. A selection of the most promising options were tested on discreet areas of the sculpture and assessed via digital microscopy and documented via the use of star diagrams described in Additional file 1: Table S1

Aqueous-based solutions with added chelators and/or surfactants

Chelators: tri-ammonium citrate (TAC), ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA)

Non-ionic surfactants: ECOSURF™ EH-6, ECOSURF™ EH-9, Pluronic^® F-127; SURFONIC^® JL-80X, Brij™ S100

Solutions with added TAC were prepared by weight (0.5–2% w/w.) with deionised water (DI); solutions containing EDTA, DTPA and surfactants were prepared accordingly to The Modular Cleaning Program^a (at a pH of 6 or 6.5).

Blends of TAC (0.5–2% w/w.) and non-ionic surfactants (0.5–1% w/w.) were prepared in DI

As above

Adjusted water 6:6 dipped swabs rolled on average for 3 applications

Solvent-based solutions

Anionic surfactant: dioctyl sulfosuccinate, sodium salt (NaDOSS).

Disperse surfactant in hydrocarbon solvent (Shellsol^®D40) using a magnetic stirrer until complete solubilisation

As above

Shellsol^®D40 dipped swabs rolled on average for 4 applications

Water-in-oil microemulsion (mineral spirits-based) as described in Ormsby et al. [7].

Series 2–2 (20% w/w. Shellsol^®D40; 50% w/w. in total of ECOSURF™ EH-6 surfactant and co-surfactants 1-Butanol and 1-hexanol; 30% w/w. aqueous phase).

Series 2–15 (70% w/w. Shellsol^®D40; 20% w/w. in total of ECOSURF™ EH-6 surfactant and co-surfactants 1-Butanol and 1-hexanol; 10% w/w. aqueous phase).

Series 3b–8 (40% w/w. Shellsol^®D40; 30% w/w. NaDOSS surfactant; 30% w/w. aqueous phase).

Series 3b–24 (80% w/w Shellsol^®D40; 10% w/w. NaDOSS surfactant; 10% w/w. aqueous phase)

Series 2: prepare a blend of ECOSURF™ EH-6, 1-butanol and 1-hexanol (ratios 50:12.5:37.5). Add the blend of surfactant and co-surfactants to the solvent by weight and add required volume of the aqueous phase drop by drop to the mixture. Shake gently for ~ 10 s.

Series 3b: prepare a 65% w/w. NaDOSS surfactant phase in Shellsol^®D40, stirring on a magnetic stirrer until dissolved. Add the surfactant to the solvent by weight and add required volume of the aqueous phase drop by drop to the mixture. Shake gently for ~ 10 s

As above

Shellsol^®D40 dipped swabs rolled on average for 4 applications

Spreadable gels/emulsifiers

Xanthan gum (2% w/w.) in deionised water (polysaccharide)

[spreadable]

Disperse the polysaccharide powder in deionised water; allow lumps to swell and shake/leave overnight to form a smooth gel. Once ready, add the aqueous solution of choice and mix well/stir with magnetic stirrer. NB: Xanthan gum can be made up using optimised aqueous phase as the base ‘solvent’; and can also be made into an emulsion when combined with non-polar solvents (not trialed in this study)

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

Dry cotton swab and cosmetic sponge (to remove most of the gel) and adjusted water 6:6 dipped cotton swabs or cosmetic sponges rolled on average for 3–4 applications

Initial trial of confining systems prepared with only water (either deionised or adjusted water 6:6) on mock-up samples. Performance was judged based on visual observations and using digital microscopy, documented using star diagrams as described in Additional file 1: Table S2. Suitable options for the sculpture were combined with the effective cleaning fluids and tested again on mock-ups and then on discreet areas of the sculpture; assessed via digital microscopy and documented using star diagrams. Residue studies for potential cleaning systems to be used on the sculpture (i.e. emulsifiers and gels) were carried out using IR spectroscopy on mock-up samples (see Instrumentation)

Shin-Etsu KSG 350z (silicone emulsifier)

- aqueous phase 20% w/w

[spreadable]

Prepared by blending 70% w/w. silicone emulsifier^b, thinned with D5 solvent (to 80% w/w.), with an aqueous phase content of 20% w/w. (either adjusted water 6:6, or with added chelators and/or surfactants). The aqueous phase was dispersed through the diluted emulsifier drop by drop, stirred vigorously to create the emulsion either manually or by using a handheld milk-frother, followed by being extruded through a luer lock syringe needle to decrease the emulsion droplet size and increase the cleaning action [45]. NB: the aqueous phase of these emulsions can be increased up to ~ 50% by weight [14]

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

Dry cotton swab and cosmetic sponge first (to remove the majority of emulsifier) and D5 silicone solvent-dipped swabs rolled until visible residues were removed, on average for 4 applications

Hydrogels

Agarose (3% w/w.)

[applied warm, spreadable]

Disperse the polysaccharide powder in deionised water, heat the solution to ~ 90 °C while stirring until complete solubilisation

The hot solution was cooled to ~ 50 °C, and then applied with a soft brush, creating a uniform layer over the surface, and left to cool (and gel) in situ. Application time varied from 1 min up to 5 min. Removed using a spatula

Excess water released onto the surface was removed with a dry cotton swab, followed by adjusted water 6:6 dipped swabs rolled onto the surface (on average for 2 applications)

Partially hydrolysed PVAc-borax (4%:1% w/w.)

[mouldable]

Disperse hydrolysed 80PVAc in water, while stirring at room temperature until the polymer was completely dissolved; add the borax solution (prepared separately) and stir the mixture until the gel is formed

Applied with a wooden spatula, spread over the mock-up surface and moulded to enhance surface contact. Application times varied from 1 to 5 min

Excess water released onto the surface was removed with a dry cotton swab, followed by adjusted water 6:6 dipped swabs rolled on the surface (on average for 2 applications)

Nanorestore Gel^® Peggy 5

Nanorestore Gel^® Peggy 6

TT series

- aqueous content ~ 90% w/w

[flexible]

Gels dispatched ready for use in single sheets (˜10 × 15 cm), immersed in a volume of deionised water. Rinsed by immersion in deionised water for 24 h prior to use^c. Gels were pre-loaded with the cleaning solutions via immersion for 12 h

 Dried using blotting paper, or a combination of blotting paper and Evolon tissue^d (N.B. the drier the gel surface, the stickier). 1.5 × 1.5 cm gel pieces were placed on papier mâché 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. For application on the ropes (both replicas and original), the gels were cut into strips and spiralled around the rope

Not required for pure hydrogels. When uploaded with active agents, clearance involved the application of the corresponding Nanorestore Gel^® hydrogels for the same period. The gel can release excess liquid on the surface, if not blotted properly before application; the paint surface can be lightly blotted after application as appropriate

Cosmetic sponges

Boots soft cosmetic sponges

NYX Pro Beauty Wedges

SENSAI sponge cloth

Washed twice by immersion in deionised water to remove impurities and coating layer (when present)

Sponges loaded with cleaning solutions by immersion; excess liquid removed by squeezing the sponge and absorbing the remaining excess on Evolon tissue^e and blotting paper. Sponges were applied to the surface of the mock-ups/sculpture (papier-mâché section) using a gentle circular motion

Sponges and cloths loaded with active cleaning agents were cleared using the same materials loaded with adjusted water 6:6 and applied to the surface using the same circular motion