*2.5. Microfadeometry (MFT)*

Illumination was achieved with an Oriel Instruments LIK-LMP Light Intensity Controller Kit equipped with a Si Detector Head and Xe-arc lamp controlled by a Spectra-Physics power supply coupled to a thermo-Oriel Digital Flux controller. Spectra were registered using a Control Development spectrometer in the range of 380–900 nm. Light contact to the object's surface was achieved using a 100 μm diameter bifurcated fiber optic, which ensures a narrow beam radius and high light intensity. Microfading was performed on three distinct spots for each color (in the same plate and color field) for a duration of 15 minutes. ISO Blue Wool (BW) 1, 2, and 3 were used as internal standards for comparison [20]. The average ΔE76 curves were obtained using the Spectral Viewer software developed at the Getty Conservation Institute [21]. A BW equivalent scale (BWeq) was established by fitting a power function to the ΔE values at t = 15 min for BW 1, 2, and 3 [22,23]. A BWeq value was then calculated for each color by interpolation of that curve for the ΔE values at t = 15 min for each color. the value obtained is rounded to the nearest category: BWeq < 2 is highly light-sensitive; BWeq = 2, 2.5, and 3 are light-sensitive, and BWeq > 3 is moderately light-sensitive to stable. It is important to note the limitation of MFT for elucidating lightfastness beyond BWeq =3[24].
