IPERION HS Macromolecular Heritage Laboratory catalogue of services at Heritage Science Lab Ljubljana (University of Ljubljana) and Research Institute of the Institute for the Protection of Cultural Heritage Slovenia.
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A wide variety of methods for determination of material properties of polymeric/macromolecular materials are available and often tailored to the material in question. In addition to the ones below, we also offer mechanical testing, colorimetry and various types of spectroscopy, as well as scanning electron microscopy and other methods.
Method A1: Determination of Molecular Mass
The average molecular mass is an important parameter often relevant to the mechanical properties of materials, from solid PVC or CA to textiles such as silk and other natural macromolecular materials such as paper. We offer two methods:
Viscometry, useful particularly for cellulosic materials, such as paper, cotton textiles, canvas.
Size exclusion chromatography, useful for some cellulosic materials, as well as the majority of non-cross-linked polymeric materials. We have methods developed for PVC and CA, and can offer the development of methods for other polymers of historical significance.
Method A2: Determination of Polymer Additives (e.g. Plasticizers) and Degradation Products
We offer a variety of gas and liquid chromatographic methods with different detection systems for qualitative and quantitative determination of polymer additives and degradation products, such as camphor in cellulose nitrate, and various phthalates in cellulose acetate, PVC and other polymers. We also have sampling methods available for determination of their migration to the surface of an object. Similarly, degradation products, such as acids, simple sugars or monomers, usually relatively small molecules, can be determined chromatographically. These are often important markers of degradation.
Sample size: variable, depending on the amount.
Example of application: Evaluation of the oxidation process of lipids in historical parchment
Method A3: Non-destructive Determination of Material Properties Using IR Spectroscopy and Multivariate Analysis
We pioneered the development of near infrared spectroscopy (NIR) and surface mid-IR methods, e.g. ATR-FTIR, in conjunction with multivariate calibration, for non-destructive characterization of historic materials, such as paper, parchment, photographs and synthetic polymers. Non-destructive determination of pH and DP of historic paper is an most important method, valuable also as input for Method B1.
Development of new methods is often extremely time consuming and requires proper research funding, but if we have the reference materials available in our Historic Material Reference Collection, then even development of new methods is possible. Dating applications are often possible and have been developed for paper, photographs, and parchment.
The available spectrometers are movable, meaning that analysis of real objects in collections is possible.
Sample size: none, non-destructive.
Example of application: Use of non-destructive NIR spectroscopy with multivariate data analysis to date historical photographs
Method A4: Determination of proteins with immunohistochemical methods
We are one of the few laboratories who offer ELISA and IFM methods for the determination of proteins in the objects of cultural heritage (CH). We routinely provide ELISA-based identification of the most commonly used proteins. With the experience of optimizing protocols for several proteins’ extraction and antibody-based detection, we can shorten the often extremely time (and thus resource) consuming processes for the introduction of the detection capability for less-standard proteins. Moreover, mock-up preparation for ageing/degradation studies for proteins in CH is also one of our strong points.
Sample size: ELISA – as low as 1 µg of protein; IFM – as small as for any of the optical microscopy investigation
Example of application: Characterisation of ovalbumin in a paint layer from 16th Century painting of Vittore Carpaccio, Presentation at the Temple, and a paint layer of the 17th century painting from Pietro Liberi, Saint Nicholas between Saint Hermagoras and Saint Fortunatus.
Method A5: Distribution of polymers and complex organic pigments
Raman mapping and FTIR imaging give molecular distribution of materials in a sample. Raman maps are usually obtained step by step, by moving the xy stage under the microscope objective, or by utilization of a set of scanning mirrors that direct the laser beam in two spatial directions. It is usually well performing to follow the distribution of inorganic pigments and fillers, as well as complex synthetic organic pigments. FTIR imaging on the other hand can be extremely useful to follow the distribution of polymeric materials, such as oils, proteins, resins, etc. A sample can be imaged with 64×64 pixel resolution, with full spectral information contained in a pixel. By integrating the characteristic vibrational bands of a sample component, we obtain images of its distribution in the examined sample.
The methods can be used for example:
- to get insight into the layered structure of samples’ cross section
- to follow the migration of components
- to differentiate between original paint layers and later restorations
Sampling: usual sample size 1-2 mm3, or non-destructive on surfaces of objects
Examples of application: Distribution of synthetic organic pigments in contemporary paintings: Gola Muza /Naked Muse (2004), by the artist Silvester Plotajs-Sicoe, painted on canvas in an oil technique, and on the work Untitled (2001), by the artist JelkaFlis, executed in an acrylic technique on a wood support.
Based on degradation rates of heritage materials determined experimentally (e.g. for colour photographs or historic paper), we can offer environmental scenario evaluation for preventive conservation of collections. This could be entirely tailor-made or we could apply existing knowledge, specifically to library and archival collections, example available here.
Method B1: Online App for Environmental Scenario Modelling for Paper-based Collections
A self-guided app is available for the exploration of preventive and interventive conservation scenarios particularly in libraries and archives. Alternatively, we offer the development of environmental management scenarios to libraries and archives based on calculations available in the app. This development was based on the SurveNIR Reference Material Collection.
Accelerated degradation (“ageing”) uses exaggerated environmental conditions (heat, humidity, light or pollutant concentration) to speed up the degradation of materials. It can be used in order to:
Evaluate the long-term effects of specific environmental conditions within a shorter experimental time period
Evaluate the changes induced in the examined material, often with a view to develop a damage function
Evaluate the suitability of conservation materials or treatments
Accelerated degradation is typically carried out in enclosed chamber with good control of the environmental variable causing degradation.
Typically, evaluation of material properties using an appropriate method needs to be carried out simultaneously to accelerated degradation, see methods in Group A.
The amount of sample for all methods in Group C depends on the material property of interest.
Method C1: Climate chamber (T and RH)
A climate chamber is used to enable evaluation of changes of material properties during exposure to elevated temperature at different humidities. The conditions should be selected to ensure that the degradation processes remain as close to natural degradation as possible. Variation in the relative humidity (or temperature) is also a possible approach.
Example of application: Study of the effect of temperature and humidity cycling on degradation of historical paper
Method C2: Photodegradation chamber
Material changes that occur outdoors or indoors over months or years, such as fading, yellowing or embrittlement, can be simulated in the chamber within weeks. A xenon lamp with a combination of different filters (daylight, window glass, solar, storage light) can be used.
Example of application: Study of degradation of alizarin carmine exposed to a metal halide lamp for a period of30 days and followed by exposure in a climatic chamber with oscillations of temperature and relative humidity for another 30 days.
Method C3: Flow-Through System with Controlled Pollution
With this setup, an atmosphere with the desired humidity, temperature and pollutant concentration is produced and maintained inside a reactor of a significant volume (5 L), where the examined materials are placed. The effects of various environmental parameters on material degradation can be studied, including pollutants such as NO2, SO2, acetic acid, formic acid, formaldehyde etc., at concentrations close to natural concentrations.
Example of application: Study of the effect NO2 and acetic acid on historical paper
As VOCs, we here denote any volatile organic compound, from volatile acids such as acetic acid, to more complex compounds indicating object degradation, e.g. plasticizers, and to volatiles as a consequence of past treatments, e.g. pesticides. Different aspects of determination of volatile organic compounds (VOCs) can be considered:
VOCs emitted by conservation and storage materials (D1 and D2)
Emissions from heritage objects (D3 and D4)
Organic volatile pollutants (D5, D6, D7)
Setups for VOC emission analyses can be static or dynamic. Static experiments are performed in closed vessels, dynamic experiments are performed in a reactor connected to a source of airflow, the humidity or composition of which can be controlled. Temperature is controlled in both cases.
Method D1: Oddy test: testing the impact of emissions on metal coupons
The Oddy test is a procedure for evaluation of the negative impact of volatile compounds emitted from a material on selected metals: silver (Ag), lead (Pb) and copper (Cu). Materials that are usually tested are those used for storage and display (e. g. enclosures, showcases, paints, coatings).
Sample size: 2 g of tested material per 100 mL vial, in triplicate, i.e. min 6 g of tested material in total.
Method D2: Strlic test: testing the impact of emissions on cellulose (ISO/DIS 23404:2020)
The Strlic test is a method for evaluation of emissions from materials that is analogous to the Oddy test but uses pure cellulose as a reference, susceptible to a wide variety of volatiles promoting both hydrolytic and oxidative degradation. Its outcomes are thus more relevant for evaluation of risks to paper-based and cellulosic-textile-based collections.
Sample size: 3 g per test, in triplicate, i.e. min. 9 g of tested material in total.
Example of application: Cross-infection effect of polymers of historic and heritage significance on the degradation of a cellulose reference test material
Method D3: VOC emissions from macromolecular materials in dynamic mode (quantitative method).
Method D4: VOC emissions from macromolecular materials in static mode (qualitative or semi-quantitative method)
The investigated sample is enclosed in a vessel and equilibrated at a fixed humidity and temperature. Sampling by extraction is carried out in a flow of air using a desorption tube (dynamic method) or by inserting a micro-extraction device directly into the vessel (static method). Identification and quantification is carried out using gas chromatography with mass spectrometric detection.
Sample size: min 100 mg (typically), can be non-destructive.
Alternatively, the micro-extraction devices can be deployed in situ, e.g. within frames, in order to analyse the air surrounding a framed object.
Sample size: nondestructive
Example of application (dynamic method): Determination of volatile pesticides emitted from museum objects
Examples of applications (static method): Determination of chlorinated compounds emitted from wood; determination of VOCs in framed Dead Sea Scrolls.
Methods D3 and D4 can be meaningfully combined with one or more of the following methods: D5, D6, D7.
Method D5: Determination of organic acids
Organic acids (e.g. formic, acetic) are well-known pollutants in museum environments, promoting metal and glass corrosion, efflorescence of carbonaceous objects, hydrolysis of organic polymers etc. Their quantitative determination is possible in enclosed environments (e.g. storage boxes or exhibition cases) or in the general museum environment, by one of the following methods:
Active sampling of indoor air, with a charcoal sorbent packed in an absorption tube, for 4 h, normally carried out by HSLL personnel, but can be carried out by external personnel after training. The tube needs to be promptly returned to HSLL where it is analysed using ion chromatography.
Passive sampling with SKC UMEx200 passive samplers, exposed in situ for 7 days by external researchers (instructions provided), and then promptly returned to HSLL for analysis with ion chromatography.
Example of application: Pollutant monitoring at the National Museum of Slovenia
Method D6: Determination of Aldehydes
Aldehydes are less well researched pollutants in indoor environments, precursors of organic acids, and can affect metal corrosion and degradation of organic materials. They can also be a cause for health concern at high levels of exposure (e.g. after building refurbishment). Their quantitative determination is possible in enclosed environments (e.g. storage boxes or exhibition cases) or in the general museum environment:
Passive sampling with SKC UMEx 100, exposed in situ for 7 days by external researchers (instructions provided), and then promptly returned to HSLL for analysis with liquid chromatography. The typical detection limit for formaldehyde is 0.2 ppb. In addition, the following can be quantitatively determined: acetaldehyde, propionaldehyde, butyraldehyde, benzaldehyde, valeraldehyde and hexaldehyde.
Example of application: Volatile aldehydes in libraries and archives
Method D7: tVOC (total volatile organic compounds) determination
Determination can be performed with a tVOC sensor with a dynamic range of 1 ppb to 20 ppm tVOC. The sensor allows remote monitoring and recording of TVOCs using a computer and software.
Complex organic pigments and dyes are essential colouring matters found in traditional paint media, logwood inks, modern paints, or other modern materials, such as plastics. We offer Raman microscopy equipped with 7 laser excitations for their characterization.
Method E1: Surface Enhanced Raman Spectroscopy for characterization of lake pigments and dyes
Surface Enhanced Raman Spectroscopy (SERS) has proved to be an extremely sensitive analytical technique. It is based on the enhancement of the Raman signal of certain molecules when they are adsorbed or placed in the proximity of appropriate metallic nanostructures. Thus, it allows investigation of organic samples that usually do not produce sufficient signal in conventional Raman spectroscopy. It has been successfully employed for the analysis of samples of cultural heritage importance, for detection of organic dyes such as anthraquinones, flavonoids, naftoquinones, rhodamines as they are the main components in pigments or lakes used as artists’ materials. We have developed new and effective substrates for SERS that enable us to characterise complex organic pigments and dyes in traditional paint media.
Example of application: Characterisation of paints on a polychrome work of art (Posavje Museum Brežice, Slovenia)
Method E2: Characterisation of logwood inks
It is known that the dyestuff from the logwood tree was already used by the Maya in pre-Columbian times for dying textiles and body painting. Logwood inks are prepared by boiling heartwood chips from the logwood tree (Haematoxylon campechianum, a species indigenous to Mexico, Central America, and the West Indies), mixing the decoction with a variety of inorganic salts such as AlK(SO4)2·12H2O or other alums, FeSO4·7H2O, Fe(NO3)2, CuSO4·5H2O, or K2CrO4, and adding a solution of dextrin or a gum as binding medium. Different inorganic salts are added to the logwood extract solutions in order to achieve certain hues. Following traditional recipes, we have created a Raman spectral database of different logwood inks that gives us the ability to characterize them in manuscripts or drawings.
Example of application: Characterisation of the ink used by Vincent van Gogh in Street in Saintes-Maries-de-la-Mer
Method E3: Characterisation of synthetic organic pigments
By the end of the 19th century, synthetic organic pigments were gradually introduced into the market and started to replace inorganic and traditional organic pigments in artists’ media. In our laboratory, we have developed a Raman database of over 100 synthetic organic pigments, belonging to pigment classes of for example b – naphthol pigment lakes, azo, diarylide, bisacetoacetarylide, phthalocyanine, azomethine metal complexes, isoindolinone, and many more. This gives us the ability to offer characterisation of synthetic organic pigments in modern paints or coloured plastic materials.
Example of application: Spectral database of yellow synthetic organic pigments and characterisation of synthetic organic pigments in contemporary paintings from the collection of the Museum of Modern Art in Ljubljana, Slovenia.