Research

Termoluminescence (TL) as a dating technique started being used since the early '70s (Aitken 1985). TL is applied to ceramics or, more likely to all materials containing quartz or feldspars that were heated at hundreds of degrees for a long time (ceramics, terracotta, bricks, porcelain, ovens, fireplaces, burnt flints, moulding sand remains and metal slags). The accuracy of the technique is 3-5% in the age field of 50-20000 years ago.
TL is based on the property of many insulating materials to emit light after being exposed to ionizing radiations. The energy stored in specific traps during the natural irradiation process is released during heating. The electron trapping is due to defects in the crystalline matrix of minerals that form additional energy levels between the valence and conduction band. Minerals that are heated during the material firing process lose all the electrons in their additional traps and the luminescence signal is reset. From that moment natural ionizing radiations form electrons that are trapped in the metastable levels in a concentration that is linear with time.

A material age, expressed in years, is calculated as the ratio between the energy stored in the material since its firing (paleodose, or archaeological dose, expressed in Gy), and the energy absorbed during a year (annual dose, expressed in Gy/year):

age =   paleodose
           annual dose

Thermoluminescence is a destructive technique: it requires a sampling of about 10 grams of material, and the same amount of finding soil if possible. This aspect could be s sensitive issue when dealing with rare artistic or historical objects, where the preservation of its integrity is mandatory: in this case, it is possible to use the TL authentication technique, which requires a tiny amount of material.

RESEARCH LINES

Archaeological glass dating

Works dealing with the dating of mosaic tesserae usually rely on the dosimetric properties of the microcrystalline inclusions in the silica matrix rather than on the matrix itself. On the other hand, in the last decades, commercial glasses have been demonstrated to be suitable for retrospective accidental dosimetry. In the last years, we apply a protocol widely used for the mobile phones’ glasses, the so-called “pre-bleached with blue LEDs” protocol, to evaluate the archaeological absorbed dose by mosaic tesserae in order to confirm their dating based on archaeological evidence. Like in the case of commercial glasses, the TL signal from ancient tesserae presents anomalous fading and it is light sensitive. The experimental protocol circumvents these problems isolating the thermally more stable TL signal with an optical pretreatment and allowing for the determination of a fading curve for each analyzed sample. Using an integrative approach, we estimated the fading correction for these tesserae and we recovered their ages. The results are partially in agreement with those hypothesized on the historical ground and show good potentialities for the dating of amorphous glassy materials.

After thermoluminescence during the '90s Optically Stimulated Luminescence was developed (Aitken 1998). OSL is an absolute dating technique used mainly on geological sediments, but applicable to all the materials that were exposed to sunlight and successively darkened. A sediment can be dated with an accuracy of 5-10% in a time range of hundreds thousands of years.
OSL, like TL, measures the light emitted from insulating materials previously exposed to ionizing radiations. The energy stored in specific traps during the natural irradiation process is released during the exposition to specific wavelenght radiations. The electron trapping is due to defects in the crystalline matrix of minerals that form additional energy levels between the valence and conduction band. Minerals are exposed to sunlight when transportedd by wind and other environmental agents, and during this process they lose all the electrons in their additional traps and the luminescence signal is reset. When the minerals are darkened due to successive layering natural ionizing radiations form electrons that are trapped in the metastable levels in a concentration that is linear with time.

A material age, expressed in years, is calculated as the ratio between the energy stored in the material since its firing (paleodose, or archaeological dose, expressed in Gy), and the energy absorbed during a year (annual dose, expressed in Gy/year):

age =   paleodose
annual dose

OSL dating is more critical than TL, but it is essential to extend the time range of age measure in insulating materials.

RESEARCH LINES

Sediments dating

A current OSL challenge is represented by the extension of datable range limits. Upper limit is tied to the saturation of luminescence traps. To deal with this, TT-OSL (Thermally transfered OSL) and VSL (Violet Stimulated Luminescence are promising techniques, but they need further studies on the mechanisms involved in trapping and electrons recombinations, as well as the setup of affordable protocols.

The use of feldspars instead of quartz as dosimeters allows to extend the use of OSL to older samples, due to bigger saturation values of their traps. The upper age limit could be extended near to one million years, and the luminescence signal of feldspars is better and clearer than that of quartz. However, this technique suffers from some collateral effects such as anomalous fading, that is a spontaneous emptying of OSL traps greater than expected from kinetic estimation.

Surface dating

Surface dating tries to date building blocks (stones, limestone, marble, granite, sandstone, basalt) using the luminescence properties of their surfaces. OSL signal of the first millimetres in this materials has a high probability to be reset before their installation. After this, surfaces are darkened the emptied traps start to fill with electrons, regenerating the OSL signal. The events that could be dated are the building of monuments and prehistoric artifacts or a covering and/or collapse event.

Mortar dating

Mortar is a common building material, and it is unlikely reused, making it an excellent way to date different construction phases. The quartz in the sand used as binder is reset during the transfer in the construction site. In this way it is possible to date the moment of the mortar puddling.
Although, it is not improbable that the reset process of OSL traps isn't really efficient, leaving some of the traps with a residual signal. To avoid this it is possible to use SG-OSL (Single Grain OSL) in which single grains of quartz are stimulated and measured, allowing to select the most affordable luminescence signals. This technique requires affordable and tested statistical methods to be applied, which are now being studied.

DEVICES

Two Risø TL/OSL Reader Model DA-20 that enable automated measurements of thermoluminescence (TL) and Optically Stimulated Luminescence (OSL) signals.
They consists of:
- automated 48-position sample changer system built into a vacuum chamber (lowest pressure < 2 * 10^-2 mbar).
- Two exchangeable sample holders (each designed to hold 48 samples) for 9.7 mm diam. Flat sample discs or 11.65 mm diam. sample cups.
- Vacuum sensing system with automated switching on reaching desired pressure, vacuum gauge, and combined vacuum/nitrogen solenoid valves (exclusive vacuum pump).
- Lift mechanism for heater element.
- Shaped Kanthal heater strip, endpoint temperature: 700°C.
- Filter holder to allow fitting of different optical detection filters.
- Photomultiplier housing with dynode chain and m-metal shielding.
-  clusters of 870 nm IR LEDs providing > 135 mW/cm² at the sample and clusters of 470 nm blue LEDs delivering > 80 mW/cm² at sample.
- a violet stimulation attachment is based on a 405 nm, 100 mW, laser.
- Risø single grain OSL attachment equipped with a focused solid-state green laser beam (532 nm), 10 mW stabilised DPSS laser.
- a 1.48 GBq (40 mCi) ⁹⁰Sr/⁹⁰Y beta source

Radiocarbon dating is the most diffused method to date organic materials, such as wood, carbon, human and animal remains, shells, corals and more. The technique allows to date materials not older than 45000-50000 years. The little amount of material required for the analysis allows to apply the method to rare or not expendable samples (human bones, seeds...), but amplifies the risk of contamination by exogenous materials (bacteria, mushes...). The Milano Bicocca laboratory is set up to guarantee optimal cleaning conditions, using commonly agreed and continuously controlled protocols.

Radiocarbon concentration analysis is used in the bioplastic field to measure the concentration of biologically produced plastic in semifinished materials according to method ASTM D 6866-10).

Visit the price list page for a detailed list of analyzeable materials.

RESEARCH

Mortar dating:

The laboratory is involved in the "Mortar Dating Intercomparison Study (MODIS)" project, aimed at analyzing the essential conditions to guarantee an affordable dating of mortars, extracting the carbonate produced during the crystalization process. The goal is to avoid the contamination from geogenic carbonates. During the project, the involved laboratories were given a set of different mortars which were physically and chemically characterized, and successively dated using one of the available methods. The Milano-Bicocca laboratory is using a method based on a previous physical separation of geogenic and anthropogenic carbonates, followed by chemical digestion to extract elemental carbon.

DEVICES

Assembled line for carbon extraction from gaseous carbon dioxide
Vacuum line for carbonates chemical digestion
Elementar MicroCUBE CHNS elemental analyzer
Chemical laboratory for materials pretreatment

Dendrochronology is a - to the year - exact method of dating wood. Tree growth only occurs in the outer layer between the bark and the actual trunk. In temperated zones of the world there is an alternate summer growth (light wood) and autumn growth (dark wood). The thickness of the growth rings depends on the climatic conditions (humidity and temperature). This creates a pattern of individual tree rings of varying width depending on the current local climate, i.e. depending on the variations in precipitation and temperature, and sun light.
The weather variation over a number of years gives a ring width growth pattern which is characteristic for those years, like an individual fingerprint of that period.

By measuring tree growth over a long period, a local reference curve for a certain tree species can be constructed showing mean values of the differences in annual growth. The curve is constructed from tree samples of varying age where the period of growth for any sample overlaps the periods of growth for some other samples.

Matching the reference curves with those measured from samples of unknown age allows to label every growth ring with a calendar age, assessing a growth calendar period for the sample. Dendrochronology is very useful when applied to samples that are not datable with radiocarbon (e.g. samples in the 1600-1900 AD period).

DEVICES

16MP camera, 90mm equivalent and 120 equivalent macro fixed lenses
Coorecorder v7.5 measuring software
CDendro v7.5 analysis software
Public NOAA dendrochronological curves

The rehydroxylation process involves the adsorption of oxydril groups (OH^-) in ceramic materials after intense heating (>500°C). It is time-related, as the fourth-root of time, and it can be used to find the period of the firing of bricks and ceramics measuring the oxydril groups mass in the material and the oxydril adsorption rate. Many parameters involved in the process have been exploited since its application in the Cultural Heritage field, but there are still many open research topics, such as the role of non-bonded oxydril groups or the thermal history of the material on oxydril intake.

RESEARCH

Process parameters:

The laboratory collaborates with the Engineering Department of Manchester University and the Queen's University in Belfast to plan an agreed dating method that takes into account the more relevant structural and kinetic parameters of the ceramic materials.

DEVICES:

Quantachrome Aquadyne DVS2 automated, gravimetric sample water vapor sorption analyzer

X-Ray fluorescence (XRF) is a non-destructive technique that measures the X-Ray emission characteristic of the atoms to determine the elemental chemical composition of the material. In some cases, it is possible to evaluate quantitatively the ratio of the elements. There is no need for sample pretreatment, and the analysis can be performed in situ, a relevant parameter in Cultural Heritage field. The data are reported in energy vs. fluorescence intensity graphs, where every peak characterizes an element. In this way, it is possible to identify original pigments compositions or eventual restoration works.

The analysis is really fast (1-2 minutes), allowing the mapping of several areas of the object, revealing for example different chromatic hatchings. The technique's main limitation is the impossibility to reveal elements with a low atomic number; our devices allow the detection of elements with atomic numbers equal to or higher than aluminum. This implies that some organic compounds and silicates of light elements can't be identified, as well as the identification of molecular compounds. This issue can be overcome using complementary methods, such as VIS_NIR spectroscopy.

RESEARCH LINES

Analysis, mathematical modeling, and interpretation of data from paintings

We are developing methods to optimize data acquired from scanning XRF devices, in particular, elemental distribution maps; this will allow a simpler interpretation of the results compared with maps obtained with other sources and detectors, as well as a match with reference databases.

Qualitative and quantitative analysis of uneven/layered samples in historical/artistic/archaeological fields

XRF is not suitable for uneven samples, because the information is mediated over the thickness crossed by the primary X radiation. We are studying experimental and mathematical methods to extract useful information even from this kind of mixed spectra.

GE-XRF (Grazing-Emission XRF)

We are tuning the device in our laboratory to operate in "grazing-emission" mode.

DEVICES

Portable Artax 200 Bruker spectrometer, with a 25 mm² Large Silicon Drift Detector, a 12 µm Be window, MnKα resolution <135eV (Peltier cooling), measure rate over 500000 counts per second, Mo X-Ray tube (10 - 50 kV, 5 µA min - 200 µA max).

Raman spectroscopy is a molecular detection technique that uses the interaction between light and the materials to obtain information about their structure and characteristics. When the light interacts with gases, liquids or solids the photons are mainly dispersed or diffused keeping their energy (elastic or Rayleigh diffusion). A small amount of photons (about 1 every 10000000) gives energy to the material, and after the impact has a different frequency. The difference in frequency before and after the impact depends on the material. This process is called anelastic diffusion, or Raman effect (from Sir C. V. Raman, 1930 Nobel prize in Physics for this discovery). Raman diffusion is now a well-established technique used in different fields, such as medicine, materials science, and chemical kinetics analysis.

In the Cultural Heritage field, it is used in chemical characterization (pigments or deterioration products), in finding conservation problems' solutions, in the study of aging mechanisms, in the identification of production technologies or surface treatments, and in the determination of deterioration and corrosion grade of surfaces. The use of high brilliance sources, such as lasers, allows the identification of many chemical species on the base of their characteristic Raman spectrum with a non-destructive technique. Measuring the relative intensity of the spectrum peaks it is possible in some cases to perform a semiquantitative analysis of the material.

DEVICES

Portable i-Raman Plus BW Tec device configured with optical fibers, a 785 nm laser with a power of 418 mW (tunable), spectral range: 200 - 3000 cm^-1, resolution better than 5 cm^-1.

Photogrammetry, 3D laser scan and spectroscopic imaging techniques are joined to link 3D models and imaging analysis communication. It allows to give information usually flatten in 2D boards in an understandable and complete representation for users and scholars.

The application of these techniques can be documentarist or for valorization purposes, such as monitoring the conservation of polychrome objects through scheduled scans.

DEVICES

Software Agisoft Metashape
Laser scanner Nextengine
3D printer Anycubic I3
High resolution camera