Evaluation of novel cleaning systems on mock-ups of unvarnished oil paint and chalk-glue ground within the Munch Aula Paintings Project

Heritage Science

Table 2 Overview of mock-up sets before cleaning and cleaning systems tested per mock-up type

Mock-up sets	Type^a	Ageing^b	‘Pre’ cleaning	Layer thickness^c	Chalking^d rating	Water-sensitivity^e rating	Cleaning systems tested
Stage one: cleaning trials
M1 33 in total	G	1 week 30,719 kJ/m²	n/a	n/a	2	4	Options tested—SPB: wheat starch, Arbocel® A and Arbocel® B. Free liquid trials: DI water, pH and conductivity adjusted waters, buffered waters, chelating agents, surfactants. Nanorestore Gel® Peggy and Dry series: HWR, MWR, Peggy 5 and Peggy 6
	Pu	1 week 30,719 kJ/m²	n/a	n/a	1	3
	Pd	1 week 30,719 kJ/m²	n/a	n/a	2	4
Stage two: comparative cleaning tests
M2 72 in total^f	G	4 weeks 143,349 kJ/m²	Bread loaf^g	Ave.136 µm Min 44 Max 338 SD: 76	2	4	SPB: Arbocel® A CO₂-snow: gas source Nanorestore® MWR gel, 0.5% w/v citric acid/NaOH pH 6.5, 4.4 mS/cm. Clearance: MWR with water adjusted to pH 6.5 PU sponge: white, latex free
	Pu	5 weeks 159,521 kJ/m²	Bread loaf^g	Ave. 239 µm Min 176 Max 320 SD: 38	1	3	SPB: Arbocel® A CO₂-snow: gas source Nanorestore® Peggy 6 gel, 1% w/v citric acid/NaOH pH 6.5, 9.2 mS/cm. Clearance: Peggy 6 with water adjusted to pH 6.0 PU sponge: white, latex free
	Pd	5 weeks 159,521 kJ/m²	Bread loaf^g	Ave. 29 µm Min 11 Max 56 SD: 13	2	4	SPB: Arbocel® A CO₂-snow: gas source Nanorestore® MWR gel, water adjusted to pH 6.0, 1000 µS/cm. Clearance: not required PU sponge: white, latex free

^aG = chalk-glue ground, Pu = undiluted cobalt blue oil paint, Pd = turpentine diluted cobalt blue oil paint. All mock-ups were composed of the following: linen canvas, hide glue size, chalk-glue ground. Pu and Pd had an additional upper layer of oil paint
^bArtificial ageing: Xenon-arc lamps indoor window glass filters, irradiance of 30–50 W/m² (300–400 nm), Black standard temperature (BST) 45 °C, chamber temperature (CHT) of 30 °C, and RH 65%
^cAverage of 300 measurements from 6 samples of each type. The layer thickness influences the vulnerability of the surface to dry mechanical and aqueous cleaning action
^dUNI EN ISO 4628-6 (2011)—part 6: assessment of degree of chalking by tape method. The rating from 0 to 5 (5 = most chalking) is based on the amount of pigment particles noted on an adhesive tape after peeling it off the painted surface and comparing it to a visual reference scale in the standard. See also Additional file 2: Table S1
^eMills et al. [46]. DI moistened swab rolls. Rating from 1 to 5 (5 = most water-sensitive)
^f12 for cleaning tests and 12 controls (3 unsoiled, accelerated aged; 3 soiled, accelerated aged; 3 unsoiled, naturally aged; 3 soiled, naturally aged)
^gUnsoiled, naturally aged controls were not bread cleaned