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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

From: Facilitating the conservation treatment of Eva Hesse’s Addendum through practice-based research, including a comparative evaluation of novel cleaning systems

Cleaning systemsTailored optionsPreparationApplicationClearanceAssessment
Aqueous solventsDeionised 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 ProgramaApplied with hand-rolled cotton swabs rolled up to 10 times, to cover an area of approximately 1 cm2Adjusted 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 solventsCyclic silicone: decamethylcyclopentasiloxane (D5)
Hydrocarbons: Shellsol®D40, Shellsol®A, Stoddard.
Not requiredAs aboveNot requiredPreliminary 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 surfactantsChelators: 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 Programa (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 aboveAdjusted water 6:6 dipped swabs rolled on average for 3 applications
Solvent-based solutionsAnionic surfactant: dioctyl sulfosuccinate, sodium salt (NaDOSS).Disperse surfactant in hydrocarbon solvent (Shellsol®D40) using a magnetic stirrer until complete solubilisationAs aboveShellsol®D40 dipped swabs rolled on average for 4 applications
Water-in-oil microemulsion (mineral spirits-based) as described in Ormsby et al. [7].Series 22 (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 215 (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 3b8 (40% w/w. Shellsol®D40; 30% w/w. NaDOSS surfactant; 30% w/w. aqueous phase).
Series 3b24 (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 aboveShellsol®D40 dipped swabs rolled on average for 4 applications
Spreadable gels/emulsifiersXanthan 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 minDry 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 applicationsInitial 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 emulsifierb, 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 minDry 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
HydrogelsAgarose (3% w/w.)
[applied warm, spreadable]
Disperse the polysaccharide powder in deionised water, heat the solution to ~ 90 °C while stirring until complete solubilisationThe 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 spatulaExcess 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 formedApplied with a wooden spatula, spread over the mock-up surface and moulded to enhance surface contact. Application times varied from 1 to 5 minExcess 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 usec. 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 tissued (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 ropeNot 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 spongesBoots 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 tissuee and blotting paper. Sponges were applied to the surface of the mock-ups/sculpture (papier-mâché section) using a gentle circular motionSponges 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
  1. ahttp://cool.conservation-us.org/byauth/stavroudis/mcp/ (accessed 07.02.2020)
  2. bNote that formulations for KSG-350z systems now generally have 10–25% emulsifier, 25–40% D5 solvent and 30–50% aqueous phase for sensitive painted surfaces; hence the KSG system used in this study was relatively emulsifier-rich
  3. c Upon arrival, the gels were transferred to closed containers (i.e. plastic or glass containers with lids used for food storage) and immersed in deionised water for 24 h; the water was changed once. In these conditions, the gels are stable and can be stored at room temperature and in the dark for several months. After rinsing, and blotting, the gel can be used as it is (i.e. as a hydrogel) or loaded with an aqueous-based solution (and some polar solvents) by immersion in the required cleaning solution for at least 12 h. Guidance on the use of the Nanorestore Gel® Peggy series can be found at this link: http://www.csgi.unifi.it/products/gel.html (accessed 07.02.2020)
  4. d Available at these links: https://www.talasonline.com/Evolon and https://www.preservationequipment.com/Catalogue/Conservation-Materials/Materials-and-Fabrics/Evolon-Microfilament-Material (accessed 07.02.2020)