Description of the collection and objects
The antiquities collection of the late Carla Maria Burri (1935–2009), Director of the Italian Cultural Institute in Egypt from 1993 and 1999, was donated to the Museo Civico di Crema e del Cremasco in Winter 2010/2011 . In 2013, Christian Orsenigo was charged with the study of the artefacts, under the supervision of Dr. Francesco Muscolino of the Soprintendenza Archeologia della Lombardia. The collection consists of about eighty objects and covers a vast time span; ranging from the most ancient item—a faience tile once belonging to the decoration of the walls of the galleries underneath Djoser’s Step Pyramid at Saqqara (ca. 2630–2611 B.C.E.)—excluding some flints actually under study—to Islamic glass dating to the 11th C. (Orsenigo 2016, forthcoming). The collection includes objects belonging to different typologies, such as funerary statuettes (shabtis) from the late New Kingdom, masks and parts of sarcophagi, bronzes and amulets, other than Hellenistic and Roman terracotta figurines and lamps. In this work we examine a Cartonnage and a Mask.
The polychrome cartonnage fragment probably comes from the back terminal of a mask, depicting a human-headed ba-bird, crowned with solar disc and holding two maat-feathers at each wing. Unfortunately nothing is known about the provenance of this object, as is the case for a very similar fragment kept at the Petrie Museum, UCL (accession number UC45900), that is a particularly good comparandum  The material is linen covered with plaster and then painted. Cartonnages such as this can be dated from Ptolemaic to Roman Periods 
Even if preserved only in its upper front part, the object is likely a miniature painted terracotta comic mask of an actor playing a slave character in the New Comedy. It shows a broad nose, brows flying up to the sides and wrinkled forehead. It can be dated to the Ptolemaic Period. See references for comparisons with similar objects [25, 26].
A painted model sample of Egyptian blue pigment (Kremer pigmente, GmbH) was prepared and analysed. The pigment, dispersed in Plextol, was applied as a painted layer on a glass substrate.
Time-resolved photoluminescence imaging
The TRPL imaging device is, described in detail elsewhere, and is summarized below. A schematic diagrame of the setup can be found elsewhere . The device is comprised of a ns laser excitation source combined with a time-gated intensified camera (C9546-03, Hamamatsu Photonics, Hamamatsu City, Japan), capable of high speed gating to capture images of transient phenomena. A custom-built trigger unit and a precision delay generator (DG535 Stanford Research System, Sunnyvale, CA, USA) complete the system, which has a net temporal jitter close to 0.5 ns.
The Q-switching laser source (FTSS 355-50 Crylas GmbH, Berlin, Germany), based on the third harmonic of a diode-pumped Nd:YAG crystal (λ = 355 nm, Pulse energy = 70 μJ, Pulse duration = 1.0 ns, repetition frequency = 100 Hz), has been modified in order to obtain the second harmonic of the same source emission (λ = 532 nm, Pulse energy = 60 μJ, Pulse duration = 1.0 ns). By using both wavelengths we probe the PL emission of materials with different absorption spectra. The two emission lines of the laser source are collinear; hence it is easy to switch between them during measurements. In order to spectrally clean laser emissions, proper bandpass filters (FL355-10 or FL532-10, Thorlabs GmbH Germany) are employed at the exit of the laser source.
The laser beam, coupled to a silica optical fibre, is magnified with suitable silica optics in order to illuminate a circular area of about 25 cm diameter on the surface of the object, with a typical fluence per pulse below 140 nJcm−2. This very low power density does not lead to detectable changes in the intensity of emission due to photooxidation in samples following typical measurements. The kinetics of the emission is detected by the gated intensified camera, which is based on a GaAs photocathode with spectral sensitivity from 380 to 900 nm. The gate width of the camera is adjustable from 3 ns to continuous mode, depending on the kinetic properties of the surface under investigation. In this work a gate width of 5 ns was employed to detect the nanosecond kinetics of the emission from organic materials. Long-lived decay kinetics ascribed to emissions from areas painted in Egyptian blue have been effectively sampled by increasing the width to 100 µs. A proper optical highpass filter w placed in front of the camera lens in order to remove excitation light: the B + W UV/IR Cut 486 M MRC filter (Schneider Optics), with high transmission from 380 to 720 nm, was employed for lifetime analysis following 355 nm excitation, whereas the Kodak Wratten 23A filter transmitting light beyond 550 nm was employed for measurements at 532 nm excitation.
As has been shown in previous research, the short temporal jitter of the system is key to the estimation of ns lifetimes which may be used to differentiate organic binding media and pigments . TRPL imaging is achieved through the reconstruction of the effective lifetime map based on a simple mono-exponential decay model .
Laser-induced photoluminescence spectroscopy
A compact spectrometer and the same dual-wavelength laser source employed in the TRPL imaging device were used for detecting emission spectra from selected points on objects. The compact spectrometer (TM-CCD C10083CA-2100, Hamamatsu Photonics) mounts a back thinned CCD image sensor and a transmission-type grating, recording spectra between 320–1100 nm with a spectral resolution of 6 nm. Through fibre optics both the laser and the spectrometer are remotely connected to an optical probe, working in the 45–0° configuration mode. Proper transmission high-pass filters (FEL420 or FEL550, Thorlabs GmbH Germany) are mounted on the probe which, that allow excitation and collection of photons from a point on surface of approximately 1 mm diameter at a distance of 35 mm. The probe is equipped with a proper transmission high-pass filter (FGL420 or FELH550, Thorlabs GmbH Germany) depending on the employed laser wavelength. Spectra are reported following background subtraction (mainly related to the sensor read and dark noise) and correction for the spectral efficiency of the device.
As proposed in past research [7, 8], a commercial Nikon D7100 digital camera (D60) was employed for recording UV-induced digital images of the PL emission of objects. Excitation was provided from a Xenon-based flash equipped with an UV bandpass filter (DUG11, Schott AG), whereas a transmission filter blocking light in the UV and in the NIR spectral range (W UV/IR Cut 486 M MRC filter, Schneider Optics) was mounted in front of a 50-mm focal camera lens [7, 8]. Similarly, infrared digital photography of the emission of Egyptian Blue painted objects was performed using the commercial digital camera without the infrared blocking filter (supplied by Advanced Camera Services, UK) and mounting an). An infrared transmission filter (R72, HOYA) was placed in front of the camera lens  for detection only of the infrared emission. Excitation of PL emission was achieved using a 15 W Watt green LED-based lamp with emission in the green (4000 lx @ 1 m) (FLAT PAR CAN RGB 10 IR WH, Cameo (Germany)).