radiocarbon dating

Radiocarbon or 14C dating is a technique used to date objects.

This method was developed in the 1940s by a group of scientists at the University of Chicago, led by Willard F. Libby; As a result, Libby received the Nobel Prize in Chemistry in 1960.[2]​.

The method begins with the measurement of carbon-14, a weakly radioactive isotope of carbon, and ends with the calibration of radiocarbon dates, transformed into calendar years.

The unstable and radioactive carbon-14, called radiocarbon, is a natural isotope of carbon. When a living being dies, it stops interacting with the biosphere and the carbon 14 in it remains unaffected by the biosphere, although it naturally decays.[3]​.

Optical methods and surface studies

Technique of close observation of objects and/or samples by means of an optical microscope that uses a system of two or more lenses (eyepiece and objective); For this the sample must be illuminated. Depending on its position with respect to the source, it can reflect light or be passed through by it.

In conservation, it can be used to observe both samples taken from objects and for direct observation, or as an auxiliary means of magnification during especially delicate phases of conservation operations.[4]​.

The scanning electron microscope is an instrument that allows the observation and surface characterization of inorganic and organic materials, providing morphological information of the analyzed material.

In the arts it is mainly used to obtain a microstructural characterization of materials such as: identification, analysis of crystalline phases and phase transitions in various materials such as metals, ceramics, composite materials, semiconductors, polymers and minerals; surface composition and grain size; assessment of material deterioration, determination of the degree of crystallinity and presence of defects.[5]​.

Petrographic microscopy is an analytical technique, mostly in the domain of geologists, that allows the mineral species present in a sample to be identified "at a glance" by observing their optical properties and textures. The petrographic microscope uses polarized light.

Depending on the structure of a crystal, the growth in each of the three dimensions will be different and the symmetry elements will also be different. This provides the glass with very important optical properties that are revealed when polarized light passes through it.[6]​.

In conservation and restoration it is used to identify various crystalline structures, pigments, lipids, proteins, etc.

The fluorescence microscope incorporates a special lamp that emits an exciting light from the fluorochromes, with which the samples to be observed are stained, and which also has a special filter that allows the light emitted by the fluorochrome to pass through.

In this analysis, the types of binders, pigments, natural resins, varnishes can be obtained.[7]​.

Confocal microscopy is based on a principle similar to that of a fluorescence microscope, but uses two confocal diaphragms (one before the sample and one after) capable of focusing the illumination on a single point on the sample. A laser is used as a light source, and with it the sample is scanned throughout its volume, plane by plane, creating a large number of two-dimensional images that a computer interprets, from which it finally generates a three-dimensional image of the object. To observe preparations with this microscope it is necessary to stain them with fluorescent substances or label them with substances conjugated to fluorochromes, such as antibodies. Through this technique, some oils, waxes, resins, etc. can be identified.

Chromatographic techniques

Gas chromatography is a technique for separating molecules; It is a function of different properties such as size, charge, etc., and is based on a column where the mobile phase is a carrier gas. The volatilized sample is introduced by drag with a carrier gas into a column containing a stationary phase, which selectively retains the sample components. Due to this selective retention, the components leave the column separately and the separated fractions pass through a detector, which responds with a recordable signal.[8]​.

The common characteristic of all types of chromatography is the existence of a mobile phase and a stationary phase. The mobile phase is the one that carries the sample and the stationary phase is the one that retains it depending on the criterion to be chosen (size, polar/apolar nature, etc.).

In many cases, this technique is coupled to mass spectrometry, which reanalyzes these phases emerging from the chromatographic column according to their mass. It is used for the analysis of organic compounds present in varnishes, binders, etc.

High-performance liquid chromatography consists of passing a sample at very high pressure (up to 400 atmospheres "Atmosphere (unit)") through the stationary phase. Like gas chromatography, HPLC (High Pressure/Performance Liquid Chromatography*) has two phases: mobile and stationary; The mobile phase is liquid and the stationary phase is solid, and is highly packed inside a column.

The study is used to analyze complex mixtures of non-volatile and thermo-labile components such as proteins of some binders or organic compounds of some natural dyes.[9]​.

Thin plate chromatography differs quite a bit from the previous two (GC and HPLC) in terms of equipment configuration. While the other two require significant instrumental equipment (injectors, chromatographs, detectors, etc.), this one is much simpler. In this case, the stationary phase is a layer of an adsorbent (for example, silica gel or alumina) held on a sheet of aluminum or glass and the mobile phase (eluent) is a volatile solvent or solvent mixture.

The sample to be analyzed is deposited near one end of a plastic or aluminum sheet that has previously been coated with a thin layer of adsorbent (stationary phase). The slide is then placed in a closed cuvette containing one or more mixed solvents (eluent or mobile phase). As the solvent mixture rises by capillarity through the adsorbent, a differential distribution of the products present in the sample between the solvent and the adsorbent occurs.[10]​.

This technique is mainly used for the study of varnishes.

Infrared spectroscopy

Infrared spectroscopy (or IR spectroscopy) is a type of absorption spectrometry that uses the infrared region of the electromagnetic spectrum.[11] Absorption spectrometry refers to a variety of techniques that employ the interaction of electromagnetic radiation with matter. In this, the intensity of a light beam measured before and after interaction with a sample is compared. In IR spectrometry, the sample is placed under a beam of infrared light and in a matter of seconds a spectrum is produced that indicates the amount of light absorbed, which enters the detector that displays the results in the form of a graph.

Some important characteristics of this analysis are:[12]​.

• - If two molecules are made up of different atoms or have different isotopic distribution, configuration or are found in different environments, the infrared spectra will be different.

• - A defined substance can be identified by its infrared spectrum.

• - These spectra can be considered as the fingerprints of said substance.

In conservation it is used to characterize natural and synthetic materials.

RAMAN spectroscopy is a non-invasive, photonic, high-resolution technique that provides chemical and structural information of almost any organic and inorganic material in a few seconds, thus allowing its identification. It is mainly used for the determination of pigments.

The technique is based on the examination of the light scattered by a material when a monochromatic beam of light falls on it. It is based on the inelastic scattering (or Raman scattering) of monochromatic light, which generally comes from a laser in the visible, near-infrared, or near-ultraviolet range. The laser light interacts with photons or other excitations in the system, so the energy of the laser photons shifts up or down.[13]​.

Rx diffraction is a fundamental technique for the study of crystalline materials that allows us to know the degradation and behavior based on the type of constituent elements. Most solids have a crystalline structure and this is different in each material. The atoms of a crystal form planes (grouped in families) that can be more or less dense.

Each time the radiation (Rx) hits a family of planes (crystals) at the appropriate angle, constructive interference (in-phase waves) occurs, is read by the detector, and a peak appears on the diffractogram or graph. The diffractograms are unique for each type of crystalline substance, analogous to a fingerprint, which allows the phase present in the sample to be identified.[14]​.

Physical studies and global exams

• - Visible light: Helps document the state of conservation and the changes or deteriorations that occur in the works. Photographs are taken with natural light and normal filters.

• - Transmitted light: Allows you to see the solidity and state of conservation of supports, watermarks on paper, etc. They are photographs taken with a light source placed on the back of the work in order to see, from the front of it, the amount of light that manages to pass through it.

• - Grazing light: This type of light increases or highlights the surface, which allows you to observe the reliefs and/or deterioration of the work such as lifting, cracks, deformations, textures, among others. It consists of taking photographs with a light that shines on the work from the side.

• - UV light: This type of light allows us to observe and identify previous interventions, or materials used such as binders, pigments, resins, varnishes, etc. For this type of photography it is necessary to use a UV light source and personal safety protective equipment.

Radiography is a technique that is used to observe the entire piece from the surface to the interior, which passes through it and impresses it on a radiographic plate. Thanks to this technique, you can locate the geometric shape of structural parts, assemblies, fixing elements, galleries and insect attacks, size gaps in their polychromy, identify previous interventions, locate metal elements, etc.

The procedure consists of exposing what you intend to photograph to a source of radiation, that is, X-rays are emitted on the part of the work whose interior you wish to observe. X-rays have the ability to pass through some materials and others absorb radiation. In this way, by placing a special detector behind the piece, the x-rays generate the image. Some areas that absorb the X-rays remain white and the rest of the components in different shades of gray, according to the density. The void, finally, remains black.[15]​.

IR digital photography is a method that is based on taking photos with infrared light that is outside the spectrum and that our eyes are not able to see with the naked eye; This is achieved through special filters that only allow the spectrum of these rays to pass through, allowing different characteristics of the work to be observed that are also not visible such as the preparatory drawing, the author's regrets in the composition of his work, drafts or sketches. This, especially in those that have a carbon base.[16]​.

radiocarbon dating

Radiocarbon or 14C dating is a technique used to date objects.

This method was developed in the 1940s by a group of scientists at the University of Chicago, led by Willard F. Libby; As a result, Libby received the Nobel Prize in Chemistry in 1960.[2]​.

The method begins with the measurement of carbon-14, a weakly radioactive isotope of carbon, and ends with the calibration of radiocarbon dates, transformed into calendar years.

The unstable and radioactive carbon-14, called radiocarbon, is a natural isotope of carbon. When a living being dies, it stops interacting with the biosphere and the carbon 14 in it remains unaffected by the biosphere, although it naturally decays.[3]​.

Optical methods and surface studies

Technique of close observation of objects and/or samples by means of an optical microscope that uses a system of two or more lenses (eyepiece and objective); For this the sample must be illuminated. Depending on its position with respect to the source, it can reflect light or be passed through by it.

In conservation, it can be used to observe both samples taken from objects and for direct observation, or as an auxiliary means of magnification during especially delicate phases of conservation operations.[4]​.

The scanning electron microscope is an instrument that allows the observation and surface characterization of inorganic and organic materials, providing morphological information of the analyzed material.

In the arts it is mainly used to obtain a microstructural characterization of materials such as: identification, analysis of crystalline phases and phase transitions in various materials such as metals, ceramics, composite materials, semiconductors, polymers and minerals; surface composition and grain size; assessment of material deterioration, determination of the degree of crystallinity and presence of defects.[5]​.

Petrographic microscopy is an analytical technique, mostly in the domain of geologists, that allows the mineral species present in a sample to be identified "at a glance" by observing their optical properties and textures. The petrographic microscope uses polarized light.

Depending on the structure of a crystal, the growth in each of the three dimensions will be different and the symmetry elements will also be different. This provides the glass with very important optical properties that are revealed when polarized light passes through it.[6]​.

In conservation and restoration it is used to identify various crystalline structures, pigments, lipids, proteins, etc.

The fluorescence microscope incorporates a special lamp that emits an exciting light from the fluorochromes, with which the samples to be observed are stained, and which also has a special filter that allows the light emitted by the fluorochrome to pass through.

In this analysis, the types of binders, pigments, natural resins, varnishes can be obtained.[7]​.

Confocal microscopy is based on a principle similar to that of a fluorescence microscope, but uses two confocal diaphragms (one before the sample and one after) capable of focusing the illumination on a single point on the sample. A laser is used as a light source, and with it the sample is scanned throughout its volume, plane by plane, creating a large number of two-dimensional images that a computer interprets, from which it finally generates a three-dimensional image of the object. To observe preparations with this microscope it is necessary to stain them with fluorescent substances or label them with substances conjugated to fluorochromes, such as antibodies. Through this technique, some oils, waxes, resins, etc. can be identified.

Chromatographic techniques

Gas chromatography is a technique for separating molecules; It is a function of different properties such as size, charge, etc., and is based on a column where the mobile phase is a carrier gas. The volatilized sample is introduced by drag with a carrier gas into a column containing a stationary phase, which selectively retains the sample components. Due to this selective retention, the components leave the column separately and the separated fractions pass through a detector, which responds with a recordable signal.[8]​.

The common characteristic of all types of chromatography is the existence of a mobile phase and a stationary phase. The mobile phase is the one that carries the sample and the stationary phase is the one that retains it depending on the criterion to be chosen (size, polar/apolar nature, etc.).

In many cases, this technique is coupled to mass spectrometry, which reanalyzes these phases emerging from the chromatographic column according to their mass. It is used for the analysis of organic compounds present in varnishes, binders, etc.

High-performance liquid chromatography consists of passing a sample at very high pressure (up to 400 atmospheres "Atmosphere (unit)") through the stationary phase. Like gas chromatography, HPLC (High Pressure/Performance Liquid Chromatography*) has two phases: mobile and stationary; The mobile phase is liquid and the stationary phase is solid, and is highly packed inside a column.

The study is used to analyze complex mixtures of non-volatile and thermo-labile components such as proteins of some binders or organic compounds of some natural dyes.[9]​.

Thin plate chromatography differs quite a bit from the previous two (GC and HPLC) in terms of equipment configuration. While the other two require significant instrumental equipment (injectors, chromatographs, detectors, etc.), this one is much simpler. In this case, the stationary phase is a layer of an adsorbent (for example, silica gel or alumina) held on a sheet of aluminum or glass and the mobile phase (eluent) is a volatile solvent or solvent mixture.

The sample to be analyzed is deposited near one end of a plastic or aluminum sheet that has previously been coated with a thin layer of adsorbent (stationary phase). The slide is then placed in a closed cuvette containing one or more mixed solvents (eluent or mobile phase). As the solvent mixture rises by capillarity through the adsorbent, a differential distribution of the products present in the sample between the solvent and the adsorbent occurs.[10]​.

This technique is mainly used for the study of varnishes.

Infrared spectroscopy

Infrared spectroscopy (or IR spectroscopy) is a type of absorption spectrometry that uses the infrared region of the electromagnetic spectrum.[11] Absorption spectrometry refers to a variety of techniques that employ the interaction of electromagnetic radiation with matter. In this, the intensity of a light beam measured before and after interaction with a sample is compared. In IR spectrometry, the sample is placed under a beam of infrared light and in a matter of seconds a spectrum is produced that indicates the amount of light absorbed, which enters the detector that displays the results in the form of a graph.

Some important characteristics of this analysis are:[12]​.

• - If two molecules are made up of different atoms or have different isotopic distribution, configuration or are found in different environments, the infrared spectra will be different.

• - A defined substance can be identified by its infrared spectrum.

• - These spectra can be considered as the fingerprints of said substance.

In conservation it is used to characterize natural and synthetic materials.

RAMAN spectroscopy is a non-invasive, photonic, high-resolution technique that provides chemical and structural information of almost any organic and inorganic material in a few seconds, thus allowing its identification. It is mainly used for the determination of pigments.

The technique is based on the examination of the light scattered by a material when a monochromatic beam of light falls on it. It is based on the inelastic scattering (or Raman scattering) of monochromatic light, which generally comes from a laser in the visible, near-infrared, or near-ultraviolet range. The laser light interacts with photons or other excitations in the system, so the energy of the laser photons shifts up or down.[13]​.

Rx diffraction is a fundamental technique for the study of crystalline materials that allows us to know the degradation and behavior based on the type of constituent elements. Most solids have a crystalline structure and this is different in each material. The atoms of a crystal form planes (grouped in families) that can be more or less dense.

Each time the radiation (Rx) hits a family of planes (crystals) at the appropriate angle, constructive interference (in-phase waves) occurs, is read by the detector, and a peak appears on the diffractogram or graph. The diffractograms are unique for each type of crystalline substance, analogous to a fingerprint, which allows the phase present in the sample to be identified.[14]​.

Physical studies and global exams

• - Visible light: Helps document the state of conservation and the changes or deteriorations that occur in the works. Photographs are taken with natural light and normal filters.

• - Transmitted light: Allows you to see the solidity and state of conservation of supports, watermarks on paper, etc. They are photographs taken with a light source placed on the back of the work in order to see, from the front of it, the amount of light that manages to pass through it.

• - Grazing light: This type of light increases or highlights the surface, which allows you to observe the reliefs and/or deterioration of the work such as lifting, cracks, deformations, textures, among others. It consists of taking photographs with a light that shines on the work from the side.

• - UV light: This type of light allows us to observe and identify previous interventions, or materials used such as binders, pigments, resins, varnishes, etc. For this type of photography it is necessary to use a UV light source and personal safety protective equipment.

Radiography is a technique that is used to observe the entire piece from the surface to the interior, which passes through it and impresses it on a radiographic plate. Thanks to this technique, you can locate the geometric shape of structural parts, assemblies, fixing elements, galleries and insect attacks, size gaps in their polychromy, identify previous interventions, locate metal elements, etc.

The procedure consists of exposing what you intend to photograph to a source of radiation, that is, X-rays are emitted on the part of the work whose interior you wish to observe. X-rays have the ability to pass through some materials and others absorb radiation. In this way, by placing a special detector behind the piece, the x-rays generate the image. Some areas that absorb the X-rays remain white and the rest of the components in different shades of gray, according to the density. The void, finally, remains black.[15]​.

IR digital photography is a method that is based on taking photos with infrared light that is outside the spectrum and that our eyes are not able to see with the naked eye; This is achieved through special filters that only allow the spectrum of these rays to pass through, allowing different characteristics of the work to be observed that are also not visible such as the preparatory drawing, the author's regrets in the composition of his work, drafts or sketches. This, especially in those that have a carbon base.[16]​.