The care of cultural heritage has a long history within the traditions of fixing and repairing objects,[10]​ and in the restorations of individual works of art. Although object restoration activities date back to the beginning of humanity, as a public and professional activity, it began in the 2nd century. In the past, restoration interventions were carried out mainly on objects of ritual use; in Mexico, vessels have been found that were broken and then joined together by means of a seam.[11] Pliny the Elder already mentions in his Natural History techniques for removing murals, a common practice among the Romans who in this way looted Greek buildings. During the Middle Ages and the Renaissance, restoration work was carried out by artisans, but with the advent of the concept of the artist, these activities began to be delegated to marginalized artisans.

It is not until the century that people only dedicated to conserving, maintaining and in some cases reconstructing objects from the past begin to emerge. The fields of science and art became increasingly interdependent thanks to scientists like Michael Faraday who began studying the harmful effects of the environment on works of art. Louis Pasteur also carried out scientific analyzes of painting during this period.[12] However, perhaps the first organized attempt to conserve cultural heritage was the Society for the Protection of Ancient Buildings in the United Kingdom. Influenced by the writings of John Ruskin, this society was founded by William Morris in 1877. During the same period, a movement with similar objectives had also developed in France under the direction of Eugène Viollet-le-Duc, a French architect and theorist who can be considered the first restorer. Viollet-le-Duc made an extensive study of Gothic architecture and set out to reconstruct and complete the unfinished works of the period. He is also one of the first to put his ideas and methods in writing; as well as being one of the first to be publicly criticized by Ruskin.

The development of modern heritage conservation received a boost in Germany, when in 1888 Friedrich Rathgen became the first chemist to be employed by a museum, the Royal Museum in Berlin. He not only developed a scientific approach to the care of objects in collections, but disseminated this approach with the publication of a Conservation Manual in 1898.[13] Over the century conservation science has become increasingly important in providing information physical, chemical, biological, geological, etc., on the materials and environment of cultural assets, allowing the identification of the causes of deterioration, the mechanisms of degradation and proposing methodologies for the characterization and protection of the assets.[14]​.

Already at the end of the century, a trend began to give foundation to the practices of rescuing objects from the past, beginning in Italy with the works of Camillo Boito. With the assumption of Fascist Italy, a work of restoration and reconstruction of the country's Roman and Renaissance past began, which created the conditions for the later creation of the Istituto Centrale per il Restauro. In this institution, the best-known restoration theorist, Cesare Brandi, emerged.

The need to establish principles to regulate the conservation and restoration of historical monuments was expressed in the “Venice Charter” or International Charter on the conservation and restoration of monuments and sites, signed in 1964.

Despite the great efforts and contributions of various specialists, restoration and conservation currently continues to be a discipline with an "unconsolidated conceptual body",[15]​ and therefore the theoretical guidelines that the interventions follow may vary according to the geographical context, the type of object intervened and even the training of the specialist. New professional figures have been created around this discipline, such as conservation scientists&action=edit&redlink=1 "Conservation science (cultural heritage) (not yet written)"), who contribute to the process of studying objects, to understanding the processes of degradation and to developing new materials and intervention techniques.[16]​.

Conservation is a professional discipline with an interdisciplinary nature, it continually develops criteria, methodologies, actions and measures that aim to safeguard tangible cultural heritage), ensuring its accessibility,[17] prolonging and maintaining for as long as possible without deterioration the materials that constitute the work, the values attributed to them and converting the object into cultural heritage. These measures and actions must respect its authenticity, the meaning and the physical properties of the cultural asset, as well as the documentary value, the signs of time and the transformations of the materials when not put the object at risk.[18]​.

Conservation is a critical act, it unites practical, technical and theoretical terms in the activities that concern it; The conservators interpret the values ​​recognized in the cultural asset, and create a work strategy delimited by ethical axes of the profession itself, as well as letters, agreements, documents, conventions, as well as local and international legislation.

Conservation is divided into three fields of action: preventive conservation, curative or direct conservation and restoration.

It consists of all those measures, policies and actions that aim to avoid, delay or minimize future deterioration or losses in cultural heritage. These actions are carried out on the context (the causes of deterioration) or the area surrounding the property, or more frequently a group of assets, without taking into account their age or condition. These measures and actions are indirect, that is, they do not interfere with the materials and structures of the objects, they do not modify their appearance, they seek to ensure that restoration and curative or direct conservation are not the first conservation option.[19]​ Preventive conservation is considered the most effective system to promote the long-term preservation of cultural assets.[20]​ Some examples are: lighting, relative humidity control, temperature control, registration, packaging, plans and risk management.[21]​.

Curative, direct or active conservation are all those actions applied directly to an asset or a group of cultural assets that aim to stop the harmful processes present or reinforce its structure (structural effects and deteriorations). These actions are only carried out when the assets are in a state of notable fragility or are deteriorating at a high rate, so they could be lost in a relatively short time. These actions sometimes modify the appearance of the goods, their purpose is to give a longer life to the object without losing the properties that define it as cultural heritage and that it experiences the least possible amount of alterations.[22]​ Among these activities are: consolidation, elimination of corrosion products, desalination, deacidification, disinfestation.[23]​ Also mechanical and physicochemical cleaning, relining, fixing, to mention a few.

Contenido

La restauración hace referencia a todas aquellas acciones aplicadas de manera directa a un bien individual y estable, que tengan como objetivo facilitar su apreciación, comprensión y uso (efectos estéticos y a sus valores). Estas acciones solo se realizan cuando el bien ha perdido una parte de su significado o función a través de una alteración o un deterioro pasados. En la mayoría de los casos, estas acciones modifican el aspecto del bien, buscan devolver al objeto su significado, y preservarlo para el futuro. Ejemplos: Reintegración cromática, unión de fragmentos, corrección de deformaciones, por mencionar algunos.[24]​.

Para reforzar lo anterior, se menciona la reflexión de Carlos Chanflón Olmos hace sobre la finalidad de la Restauración “proteger las fuentes objetivas del conocimiento histórico”,[25]​ dicha situación conlleva una acción responsable por proteger los bienes culturales. Por tal motivo, toda actividad de conservación y restauración sobre estos bienes requiere de un planteamiento crítico previo de defunción y valoración del objeto sobre el que se pretende actual. Por lo que, antes de cualquier práctica ejecutoria es necesario desarrollar “[…] una lectura previa del texto de la obra de arte [bien cultural] y, por consiguiente, una interpretación del mismo, una reacentuación valorativa de este texto entrando en diálogo con él y con las lecturas pasadas del mismo, así como anticipando posibles lecturas futuras”.[26]​.

Background

Restoration from its beginnings began as a discipline that seeks to protect historical-artistic works. In the centuries and , authors such as Eugène Viollet-le-Duc, John Ruskin, Camilo Boito, Cesare Brandi and Paul Philippot, "helped to establish techniques, theories and ethical codes that are applied in and during the intervention of artistic works today. According to Eugène Viollet-le-Duc, he sought: "return to the building the state it could have had" or "a state that it never reached have".[27]​ These words led to various practices that are currently discarded because they consisted of giving the monument to be restored the appearance it had in its beginnings. Despite not being accepted, it helped lay certain foundations for the future of this discipline. On the other hand, John Ruskin, showed a totally opposite position, saying: "let the buildings die with dignity".[27]​ This in the same way influenced the future of restoration, seeking that his methods did not alter the original form of the work in question.

Over the years, different restoration criteria have been consolidated by various authors. These criteria formed the Restauro Charters), which were made with the intention of establishing common agreement for interventions in conservation and restoration.[27] At the same time, the charters allow the creation and intervention of a multidisciplinary team, as well as the creation of previous reports pertaining to the works. Each charter receives its name with respect to the cities in which the meetings of the member countries of the organizations linked to the field of conservation and restoration were held.[28] These charters are supported by organizations. that promote conventions, charters and standards that help govern heritage conservation worldwide, such as the United Nations Educational, Scientific and Cultural Organization (UNESCO)[29]​ and the International Council on Monuments and Sites (ICOMOS)&action=edit&redlink=1 "International Council on Monuments and Sites (ICOMOS) (not yet drafted)")[29]​.

The first letter was made in 1905 in Vienna, and after this event various conventions and letters have followed until today. Some of these letters will be mentioned below:

Preparation is the term used to encompass those activities that are responsible for the treatment of geological, biological and paleontological heritage, that is, the goods or samples associated with the field of naturalia") that are usually part of museological and scientific collections, with exceptions. Mainly, this group includes rocks, minerals, sediments or fossils, as well as anthropological, zoological, botanical or mycological remains, and their cultural importance is closely linked to the values attributed to them. (for example: rarity, origin, usefulness, etc.).

Given that the objectives of the preparation are focused exclusively on promoting research work, some of the techniques used to prepare this type of specimens may have a negative effect on the state of conservation of the assets. However, various reference institutions, such as the Barcelona Museum of Natural Sciences or the Miquel Crusafont Catalan Institute of Paleontology, are pioneers in the incorporation of current conservation criteria and in interdisciplinary dialogue aimed at making compatible and balancing research and conservation work. However, this tandem is still very incipient and the laws that regulate cultural and natural heritage are far from being in harmony, which causes problems of intrusion and professional rivalry, lack of collaboration, poor training and lack of social-economic vision, among others.

Los trabajos interdisciplinares deben efectuarse de forma paralela y, tras exponer y discutir los resultados obtenidos, se tratará de establecer un diagnóstico y formular unas conclusiones adecuadas que establezcan cuál ha de ser el tratamiento de conservación y restauración más idóneo con mayores garantías y respeto hacia la obra.[27]​.

Control

The restoration begins with the opening of a file or report that accompanies the work throughout the process, and with the registration in a record book with its history, origin and data necessary for its identification. The file can be abbreviated, in the form of a standardized file, where both the characteristics of the document and its state of conservation and the procedures and products used in the treatment are noted. These sheets, which begin to be filled out in this phase, are completed throughout the restoration process and once this is completed, complementary recommendations for future conservation are included.[29]​ The entire conservation and restoration process will be recorded in writing in an exhaustive technical report, prepared by the restorer, which will be illustrated with photographs and graphs representative of the different phases and which is completed with the rest of the reports made by the laboratory staff and by the historians.[29]​.

[29]​.

Photographic documentation

The photograph is also part of the report initiated in the control phase as testimony of the state of conservation, evolution during the restoration process and final result.[29]​ The work of the photographers must reflect the initial state of the work, prior to the restoration and the different phases of the process and the final result, once said treatment has been applied. They take general shots of the different views of the three-dimensional object and the representative details from the stylistic point of view and the aspects related to the deterioration, as well as the modifications that have occurred during the intervention. This documentation is essential, not only to demonstrate the criteria followed in the work, but also as an aid to any art history research that is going to be carried out on the piece.[27]​.

Physical analysis

It serves as a reference for the iconographic study carried out by the historian, the preparation of damage maps by the restorer and the strict location of the samples that can be taken by chemists, biologists and geologists.

Infrared reflectography is a technique most frequently used in painting and rarely applied in sculpture. On the other hand, fluorescence photography with an ultraviolet lamp is of greater interest to reveal the presence of repaints, aged varnishes or losses, locate the joining joints between the pieces of a polychrome wooden work or serve as an aid in the cleaning process.[27]​.

Some physical analyzes can be performed using non-destructive testing (NDT), which are methods that can be done in situ. They are generally inexpensive and well suited for the inspection, monitoring and evaluation of historic buildings. Non-destructive testing can give results immediately: detect the state of structures, classify structures according to the current condition, and compare different properties based on threshold values.[31]​ Some non-destructive techniques can be radiography, thermography, georadar, electrical methods, magnetic particles, etc.[32]​.

Chemical analysis

The work methodology and the sequence of analysis techniques used will always depend on several factors, such as the components of the work, whether or not sampling is necessary, its size or the type of data to be obtained. The morphology of the samples is studied under an optical microscope and the succession of layers, the color and thickness of each of them, the optical characteristics of the pigments and the presence of varnishes or repaints, etc. are determined. The analysis itself is carried out using specific instrumental techniques for organic and inorganic materials. There are complex analytical techniques that can be performed taking advantage of microscopic preparation, while others require prior isolation of a tiny fragment of each layer.[27]​.

En este punto, nos referiremos, en líneas generales, a los aspectos básicos más comunes en los procesos de restauración de la obra tratada. Una parte de la restauración del patrimonio puede implicar la sustitución de la calefacción obsoleta y los sistemas de refrigeración con las más nuevas, o la instalación de controles de clima que no existían en el momento de la construcción. Tsarskoye Selo, el complejo de antiguos palacios reales fuera de San Petersburgo en Rusia son un ejemplo de este tipo de trabajo. La física de los materiales de una época anterior, que podría haber sido el estado de la técnica en el momento de la construcción, podría haber fallado, y ahora deberán ser sustituidos con una con mejor funcionamiento contemporáneo, pero estéticamente con materiales similares. La Restauración de los edificios de la Bauhaus en Dessau, Alemania Corrigieron una falla en la composición de una curva del techo.

Support treatment

It is necessary to consolidate the support of wood, stone, etc., when it has lost its consistency, and even replace pieces, although the latter should only be justified by structural needs, using materials with similar behavior against environmental factors and mechanical resistance slightly lower than the originals.

Fixation, adhesion and consolidation of the polychrome

Reinforcement of the adhesion of the primer and the pictorial film must be done whenever they require it, because they are detached from the support, or when a lack of adhesion between them is detected. The adhesive strengthens the bond between two layers or that of a layer with the corresponding support. The convenience of the products to be used will be studied according to the characteristics of the polychrome, taking into account that they should never alter its primitive appearance. Many green paints of the century were made with arsenic, a material not allowed in paints. Another problem occurs when the original pigment comes from a material that was not available. From the first part of the century mummy earth was used in the manufacture of some browns. In this case, organizations such as the British National Trust for Places of Historic Interest or Natural Beauty collaborate with a historic color paint recreator such as Farrow and Ball to reproduce the ancient color in stable, safe and environmentally friendly materials.

Cleaning and removal of repaints

Cleaning has to be homogeneous, never capricious, because if this is the case, false history and confusing finishes may be created. The intervention must be limited to the essential minimum in accordance with what is established in the work methodology decided by the commission of specialists. Whether done through mechanical means or using products whose basis of action is known, the structure or chromaticism of the work should never be altered. Materials of known composition must be used and, even so, previous tests must be carried out with solvents and other products, located in discrete areas, using a binocular magnifying glass. In no case will the cleaning be deep, since the surface appearance, or "patina" "Patina (copper)") caused by the passage of time, must always be preserved, as well as any traces of old varnishes must be respected, as long as they are not so altered that they modify the original tone and make it difficult to contemplate the polychrome.

The decision to eliminate a repolychrome can only be justified after the presentation of solid arguments. We know that, on too many occasions, these testimonies of changes in taste and style throughout history have been irremediably lost. The elimination of a repolychrome must be accepted, in any case, by an interdisciplinary commission of specialists, justifying its viability from all points of view: material, historical, aesthetic and functional. Once the elimination has been decided, before intervening, a complete description and documentation of the polychrome must be made, including all possible information about it. Located discreetly, significant witnesses of the removed polychromy should be left.[27]​.

Reinstatement

First, the work methodology must be determined, seeking to adhere mostly to the original. As regards the polychrome, the reintegrations must be justified by the recomposition of the correct reading of it. Depending on the circumstances, you can choose between various solutions: stippling, striping, spot inks, etc. If the defects, once the cleaning and consolidation process has been carried out, leave the support visible, so that its tone does not distort with the chromatic set, it will not be necessary to carry out reintegrations. Whenever possible, any document, graphic or written, that provides reliable data on its primitive appearance will be used.

Protection layer

It should be applied only when it is considered necessary to protect the work during its exhibition, avoiding alteration of the primitive finish and respecting in any case the finish typical of each artistic style.

Conservation, the activity of the conservator-restorer, consists of the technical examination, preservation and conservation/restoration of cultural property: The examination is the first step carried out to determine the original structure and components of an object, as well as the extent of the deterioration, alterations and losses it suffers and the documentation of the discoveries made. Preservation is the action undertaken to delay or prevent the deterioration or damage that cultural assets are likely to suffer, by way of controlling their environment and/or treating their structure, to keep them in a stable condition for as long as possible. Restoration is the activity carried out to render a deteriorated or damaged object identifiable, sacrificing the minimum of its aesthetic and historical integrity.[33]​.

The conservation and restoration of cultural assets requires specific training that allows the necessary treatments to be applied to the assets, so as to guarantee their transmission to the future with the greatest guarantees. For this, there are specific training centers"), such as university faculties and technical schools, where students acquire the knowledge and skills necessary to practice the profession.

To improve the working conditions of conservator restorers of cultural property, as in other countries, numerous associations linked to this professional activity have also been created in Spain.

The care of cultural heritage has a long history within the traditions of fixing and repairing objects,[10]​ and in the restorations of individual works of art. Although object restoration activities date back to the beginning of humanity, as a public and professional activity, it began in the 2nd century. In the past, restoration interventions were carried out mainly on objects of ritual use; in Mexico, vessels have been found that were broken and then joined together by means of a seam.[11] Pliny the Elder already mentions in his Natural History techniques for removing murals, a common practice among the Romans who in this way looted Greek buildings. During the Middle Ages and the Renaissance, restoration work was carried out by artisans, but with the advent of the concept of the artist, these activities began to be delegated to marginalized artisans.

It is not until the century that people only dedicated to conserving, maintaining and in some cases reconstructing objects from the past begin to emerge. The fields of science and art became increasingly interdependent thanks to scientists like Michael Faraday who began studying the harmful effects of the environment on works of art. Louis Pasteur also carried out scientific analyzes of painting during this period.[12] However, perhaps the first organized attempt to conserve cultural heritage was the Society for the Protection of Ancient Buildings in the United Kingdom. Influenced by the writings of John Ruskin, this society was founded by William Morris in 1877. During the same period, a movement with similar objectives had also developed in France under the direction of Eugène Viollet-le-Duc, a French architect and theorist who can be considered the first restorer. Viollet-le-Duc made an extensive study of Gothic architecture and set out to reconstruct and complete the unfinished works of the period. He is also one of the first to put his ideas and methods in writing; as well as being one of the first to be publicly criticized by Ruskin.

The development of modern heritage conservation received a boost in Germany, when in 1888 Friedrich Rathgen became the first chemist to be employed by a museum, the Royal Museum in Berlin. He not only developed a scientific approach to the care of objects in collections, but disseminated this approach with the publication of a Conservation Manual in 1898.[13] Over the century conservation science has become increasingly important in providing information physical, chemical, biological, geological, etc., on the materials and environment of cultural assets, allowing the identification of the causes of deterioration, the mechanisms of degradation and proposing methodologies for the characterization and protection of the assets.[14]​.

Already at the end of the century, a trend began to give foundation to the practices of rescuing objects from the past, beginning in Italy with the works of Camillo Boito. With the assumption of Fascist Italy, a work of restoration and reconstruction of the country's Roman and Renaissance past began, which created the conditions for the later creation of the Istituto Centrale per il Restauro. In this institution, the best-known restoration theorist, Cesare Brandi, emerged.

The need to establish principles to regulate the conservation and restoration of historical monuments was expressed in the “Venice Charter” or International Charter on the conservation and restoration of monuments and sites, signed in 1964.

Despite the great efforts and contributions of various specialists, restoration and conservation currently continues to be a discipline with an "unconsolidated conceptual body",[15]​ and therefore the theoretical guidelines that the interventions follow may vary according to the geographical context, the type of object intervened and even the training of the specialist. New professional figures have been created around this discipline, such as conservation scientists&action=edit&redlink=1 "Conservation science (cultural heritage) (not yet written)"), who contribute to the process of studying objects, to understanding the processes of degradation and to developing new materials and intervention techniques.[16]​.

Conservation is a professional discipline with an interdisciplinary nature, it continually develops criteria, methodologies, actions and measures that aim to safeguard tangible cultural heritage), ensuring its accessibility,[17] prolonging and maintaining for as long as possible without deterioration the materials that constitute the work, the values attributed to them and converting the object into cultural heritage. These measures and actions must respect its authenticity, the meaning and the physical properties of the cultural asset, as well as the documentary value, the signs of time and the transformations of the materials when not put the object at risk.[18]​.

Conservation is a critical act, it unites practical, technical and theoretical terms in the activities that concern it; The conservators interpret the values ​​recognized in the cultural asset, and create a work strategy delimited by ethical axes of the profession itself, as well as letters, agreements, documents, conventions, as well as local and international legislation.

Conservation is divided into three fields of action: preventive conservation, curative or direct conservation and restoration.

It consists of all those measures, policies and actions that aim to avoid, delay or minimize future deterioration or losses in cultural heritage. These actions are carried out on the context (the causes of deterioration) or the area surrounding the property, or more frequently a group of assets, without taking into account their age or condition. These measures and actions are indirect, that is, they do not interfere with the materials and structures of the objects, they do not modify their appearance, they seek to ensure that restoration and curative or direct conservation are not the first conservation option.[19]​ Preventive conservation is considered the most effective system to promote the long-term preservation of cultural assets.[20]​ Some examples are: lighting, relative humidity control, temperature control, registration, packaging, plans and risk management.[21]​.

Curative, direct or active conservation are all those actions applied directly to an asset or a group of cultural assets that aim to stop the harmful processes present or reinforce its structure (structural effects and deteriorations). These actions are only carried out when the assets are in a state of notable fragility or are deteriorating at a high rate, so they could be lost in a relatively short time. These actions sometimes modify the appearance of the goods, their purpose is to give a longer life to the object without losing the properties that define it as cultural heritage and that it experiences the least possible amount of alterations.[22]​ Among these activities are: consolidation, elimination of corrosion products, desalination, deacidification, disinfestation.[23]​ Also mechanical and physicochemical cleaning, relining, fixing, to mention a few.

Contenido

La restauración hace referencia a todas aquellas acciones aplicadas de manera directa a un bien individual y estable, que tengan como objetivo facilitar su apreciación, comprensión y uso (efectos estéticos y a sus valores). Estas acciones solo se realizan cuando el bien ha perdido una parte de su significado o función a través de una alteración o un deterioro pasados. En la mayoría de los casos, estas acciones modifican el aspecto del bien, buscan devolver al objeto su significado, y preservarlo para el futuro. Ejemplos: Reintegración cromática, unión de fragmentos, corrección de deformaciones, por mencionar algunos.[24]​.

Para reforzar lo anterior, se menciona la reflexión de Carlos Chanflón Olmos hace sobre la finalidad de la Restauración “proteger las fuentes objetivas del conocimiento histórico”,[25]​ dicha situación conlleva una acción responsable por proteger los bienes culturales. Por tal motivo, toda actividad de conservación y restauración sobre estos bienes requiere de un planteamiento crítico previo de defunción y valoración del objeto sobre el que se pretende actual. Por lo que, antes de cualquier práctica ejecutoria es necesario desarrollar “[…] una lectura previa del texto de la obra de arte [bien cultural] y, por consiguiente, una interpretación del mismo, una reacentuación valorativa de este texto entrando en diálogo con él y con las lecturas pasadas del mismo, así como anticipando posibles lecturas futuras”.[26]​.

Background

Restoration from its beginnings began as a discipline that seeks to protect historical-artistic works. In the centuries and , authors such as Eugène Viollet-le-Duc, John Ruskin, Camilo Boito, Cesare Brandi and Paul Philippot, "helped to establish techniques, theories and ethical codes that are applied in and during the intervention of artistic works today. According to Eugène Viollet-le-Duc, he sought: "return to the building the state it could have had" or "a state that it never reached have".[27]​ These words led to various practices that are currently discarded because they consisted of giving the monument to be restored the appearance it had in its beginnings. Despite not being accepted, it helped lay certain foundations for the future of this discipline. On the other hand, John Ruskin, showed a totally opposite position, saying: "let the buildings die with dignity".[27]​ This in the same way influenced the future of restoration, seeking that his methods did not alter the original form of the work in question.

Over the years, different restoration criteria have been consolidated by various authors. These criteria formed the Restauro Charters), which were made with the intention of establishing common agreement for interventions in conservation and restoration.[27] At the same time, the charters allow the creation and intervention of a multidisciplinary team, as well as the creation of previous reports pertaining to the works. Each charter receives its name with respect to the cities in which the meetings of the member countries of the organizations linked to the field of conservation and restoration were held.[28] These charters are supported by organizations. that promote conventions, charters and standards that help govern heritage conservation worldwide, such as the United Nations Educational, Scientific and Cultural Organization (UNESCO)[29]​ and the International Council on Monuments and Sites (ICOMOS)&action=edit&redlink=1 "International Council on Monuments and Sites (ICOMOS) (not yet drafted)")[29]​.

The first letter was made in 1905 in Vienna, and after this event various conventions and letters have followed until today. Some of these letters will be mentioned below:

Preparation is the term used to encompass those activities that are responsible for the treatment of geological, biological and paleontological heritage, that is, the goods or samples associated with the field of naturalia") that are usually part of museological and scientific collections, with exceptions. Mainly, this group includes rocks, minerals, sediments or fossils, as well as anthropological, zoological, botanical or mycological remains, and their cultural importance is closely linked to the values attributed to them. (for example: rarity, origin, usefulness, etc.).

Given that the objectives of the preparation are focused exclusively on promoting research work, some of the techniques used to prepare this type of specimens may have a negative effect on the state of conservation of the assets. However, various reference institutions, such as the Barcelona Museum of Natural Sciences or the Miquel Crusafont Catalan Institute of Paleontology, are pioneers in the incorporation of current conservation criteria and in interdisciplinary dialogue aimed at making compatible and balancing research and conservation work. However, this tandem is still very incipient and the laws that regulate cultural and natural heritage are far from being in harmony, which causes problems of intrusion and professional rivalry, lack of collaboration, poor training and lack of social-economic vision, among others.

Los trabajos interdisciplinares deben efectuarse de forma paralela y, tras exponer y discutir los resultados obtenidos, se tratará de establecer un diagnóstico y formular unas conclusiones adecuadas que establezcan cuál ha de ser el tratamiento de conservación y restauración más idóneo con mayores garantías y respeto hacia la obra.[27]​.

Control

The restoration begins with the opening of a file or report that accompanies the work throughout the process, and with the registration in a record book with its history, origin and data necessary for its identification. The file can be abbreviated, in the form of a standardized file, where both the characteristics of the document and its state of conservation and the procedures and products used in the treatment are noted. These sheets, which begin to be filled out in this phase, are completed throughout the restoration process and once this is completed, complementary recommendations for future conservation are included.[29]​ The entire conservation and restoration process will be recorded in writing in an exhaustive technical report, prepared by the restorer, which will be illustrated with photographs and graphs representative of the different phases and which is completed with the rest of the reports made by the laboratory staff and by the historians.[29]​.

[29]​.

Photographic documentation

The photograph is also part of the report initiated in the control phase as testimony of the state of conservation, evolution during the restoration process and final result.[29]​ The work of the photographers must reflect the initial state of the work, prior to the restoration and the different phases of the process and the final result, once said treatment has been applied. They take general shots of the different views of the three-dimensional object and the representative details from the stylistic point of view and the aspects related to the deterioration, as well as the modifications that have occurred during the intervention. This documentation is essential, not only to demonstrate the criteria followed in the work, but also as an aid to any art history research that is going to be carried out on the piece.[27]​.

Physical analysis

It serves as a reference for the iconographic study carried out by the historian, the preparation of damage maps by the restorer and the strict location of the samples that can be taken by chemists, biologists and geologists.

Infrared reflectography is a technique most frequently used in painting and rarely applied in sculpture. On the other hand, fluorescence photography with an ultraviolet lamp is of greater interest to reveal the presence of repaints, aged varnishes or losses, locate the joining joints between the pieces of a polychrome wooden work or serve as an aid in the cleaning process.[27]​.

Some physical analyzes can be performed using non-destructive testing (NDT), which are methods that can be done in situ. They are generally inexpensive and well suited for the inspection, monitoring and evaluation of historic buildings. Non-destructive testing can give results immediately: detect the state of structures, classify structures according to the current condition, and compare different properties based on threshold values.[31]​ Some non-destructive techniques can be radiography, thermography, georadar, electrical methods, magnetic particles, etc.[32]​.

Chemical analysis

The work methodology and the sequence of analysis techniques used will always depend on several factors, such as the components of the work, whether or not sampling is necessary, its size or the type of data to be obtained. The morphology of the samples is studied under an optical microscope and the succession of layers, the color and thickness of each of them, the optical characteristics of the pigments and the presence of varnishes or repaints, etc. are determined. The analysis itself is carried out using specific instrumental techniques for organic and inorganic materials. There are complex analytical techniques that can be performed taking advantage of microscopic preparation, while others require prior isolation of a tiny fragment of each layer.[27]​.

En este punto, nos referiremos, en líneas generales, a los aspectos básicos más comunes en los procesos de restauración de la obra tratada. Una parte de la restauración del patrimonio puede implicar la sustitución de la calefacción obsoleta y los sistemas de refrigeración con las más nuevas, o la instalación de controles de clima que no existían en el momento de la construcción. Tsarskoye Selo, el complejo de antiguos palacios reales fuera de San Petersburgo en Rusia son un ejemplo de este tipo de trabajo. La física de los materiales de una época anterior, que podría haber sido el estado de la técnica en el momento de la construcción, podría haber fallado, y ahora deberán ser sustituidos con una con mejor funcionamiento contemporáneo, pero estéticamente con materiales similares. La Restauración de los edificios de la Bauhaus en Dessau, Alemania Corrigieron una falla en la composición de una curva del techo.

Support treatment

It is necessary to consolidate the support of wood, stone, etc., when it has lost its consistency, and even replace pieces, although the latter should only be justified by structural needs, using materials with similar behavior against environmental factors and mechanical resistance slightly lower than the originals.

Fixation, adhesion and consolidation of the polychrome

Reinforcement of the adhesion of the primer and the pictorial film must be done whenever they require it, because they are detached from the support, or when a lack of adhesion between them is detected. The adhesive strengthens the bond between two layers or that of a layer with the corresponding support. The convenience of the products to be used will be studied according to the characteristics of the polychrome, taking into account that they should never alter its primitive appearance. Many green paints of the century were made with arsenic, a material not allowed in paints. Another problem occurs when the original pigment comes from a material that was not available. From the first part of the century mummy earth was used in the manufacture of some browns. In this case, organizations such as the British National Trust for Places of Historic Interest or Natural Beauty collaborate with a historic color paint recreator such as Farrow and Ball to reproduce the ancient color in stable, safe and environmentally friendly materials.

Cleaning and removal of repaints

Cleaning has to be homogeneous, never capricious, because if this is the case, false history and confusing finishes may be created. The intervention must be limited to the essential minimum in accordance with what is established in the work methodology decided by the commission of specialists. Whether done through mechanical means or using products whose basis of action is known, the structure or chromaticism of the work should never be altered. Materials of known composition must be used and, even so, previous tests must be carried out with solvents and other products, located in discrete areas, using a binocular magnifying glass. In no case will the cleaning be deep, since the surface appearance, or "patina" "Patina (copper)") caused by the passage of time, must always be preserved, as well as any traces of old varnishes must be respected, as long as they are not so altered that they modify the original tone and make it difficult to contemplate the polychrome.

The decision to eliminate a repolychrome can only be justified after the presentation of solid arguments. We know that, on too many occasions, these testimonies of changes in taste and style throughout history have been irremediably lost. The elimination of a repolychrome must be accepted, in any case, by an interdisciplinary commission of specialists, justifying its viability from all points of view: material, historical, aesthetic and functional. Once the elimination has been decided, before intervening, a complete description and documentation of the polychrome must be made, including all possible information about it. Located discreetly, significant witnesses of the removed polychromy should be left.[27]​.

Reinstatement

First, the work methodology must be determined, seeking to adhere mostly to the original. As regards the polychrome, the reintegrations must be justified by the recomposition of the correct reading of it. Depending on the circumstances, you can choose between various solutions: stippling, striping, spot inks, etc. If the defects, once the cleaning and consolidation process has been carried out, leave the support visible, so that its tone does not distort with the chromatic set, it will not be necessary to carry out reintegrations. Whenever possible, any document, graphic or written, that provides reliable data on its primitive appearance will be used.

Protection layer

It should be applied only when it is considered necessary to protect the work during its exhibition, avoiding alteration of the primitive finish and respecting in any case the finish typical of each artistic style.

Conservation, the activity of the conservator-restorer, consists of the technical examination, preservation and conservation/restoration of cultural property: The examination is the first step carried out to determine the original structure and components of an object, as well as the extent of the deterioration, alterations and losses it suffers and the documentation of the discoveries made. Preservation is the action undertaken to delay or prevent the deterioration or damage that cultural assets are likely to suffer, by way of controlling their environment and/or treating their structure, to keep them in a stable condition for as long as possible. Restoration is the activity carried out to render a deteriorated or damaged object identifiable, sacrificing the minimum of its aesthetic and historical integrity.[33]​.

The conservation and restoration of cultural assets requires specific training that allows the necessary treatments to be applied to the assets, so as to guarantee their transmission to the future with the greatest guarantees. For this, there are specific training centers"), such as university faculties and technical schools, where students acquire the knowledge and skills necessary to practice the profession.

To improve the working conditions of conservator restorers of cultural property, as in other countries, numerous associations linked to this professional activity have also been created in Spain.