*2.2. Methods*

The range of the applied analytical methods differed between the NGS and Liu collections, mainly due to the Liu family's wish to conduct only non-invasive in situ examination of their paintings. Thus, only visible light (VIS) photography of the characteristic features of the paint layers was conducted on paintings from the Liu collection to provide further insights into the artist's painting technique. The NGS paintings were studied first by means of non-invasive imaging techniques, comprising VIS, ultraviolet fluorescence (UVF), reflected ultraviolet (UVR), and near-infrared (NIR) photography. The aim of these non-invasive techniques was to conduct a preliminary characterisation of the pigments by recording their optical features under different wavelengths of the electromagnetic spectrum. An investigation of the paint textures was conducted with reflectance transformation imaging (RTI). To verify the presence of underlying paint layers, NIR and X-ray radiography (XRR) were carried out. The obtained results guided a sampling of the paint layers from the areas with prior loss, for characterising the paint mixtures in detail. Thus, the samples were analysed using optical microscopy (OM), polarised light microscopy (PLM), and field emission scanning electron microscope with energy dispersive spectroscopy (FE-SEM-EDS). A handheld portable X-ray fluorescence (XRF) was used to analyse some areas of the *Countryside in France* where sampling was not safe. A macro X-ray fluorescence (MA-XRF) scanner was engaged to perform the elemental mapping of *Landscape in Switzerland* and to support interpretation of data collected from the painting. The initial indication of the organic components of the paint samples was given by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). The results are summarised in Appendix A, Table A1.

**Figure 1.** Paintings by Liu Kang from the collection of National Gallery Singapore: (**a**) *Autumn colours*, 1930, oil on canvas, 38.3 × 45.3 cm; (**b**) *Countryside in France*, 1930, oil on canvas, 46 × 54.7 cm, gift of the artist's family; (**c**) *Landscape in Switzerland*, 1930, oil on canvas, 45.6 × 55.7 cm, gift of C Y Hwang; (**d**) *Village scene*, 1931, oil on canvas, 46 × 55 cm, gift of the artist's family; (**e**) *French lady*, 1931, oil on canvas, 60.7 × 45.8 cm; (**f**) *Boat near the cliff*, 1931, oil on canvas, 53.7 × 72.4 cm, gift of the artist's family; and (**g**) *Breakfast*, 1932, oil on canvas, 46 × 54 cm. Images courtesy of National Heritage Board. White arrows indicate sampling areas.

**Figure 2.** Paintings by Liu Kang from the Liu Kang Family Collection: (**a**) *St Gingolph, Lac Leman, Switzerland*, 1929, oil on canvas, 45.5 × 37.5 cm; (**b**) *Landscape*, 1930, oil on canvas, 46 × 38 cm; (**c**) *Still life with books, Paris*, 1931, oil on canvas, 45 × 38 cm; (**d**) *Portrait of a man with his pipe, Paris*, 1931, oil on canvas, 45 × 38 cm; (**e**) *Self-portrait*, 1931, oil on canvas, 55 × 46 cm; and (**f**) *My landlady, Madame Normand*, 1932, oil on canvas, 54 × 45 cm. Images courtesy of Liu family.
