A BUILT HERITAGE SERIES: AN INTRODUCTION TO SIMPLE ANALYSIS METHODS FOR: PAINTED SURFACES (PART 1 OF 1)

BUILT HERITAGE SERIES: AN INTRODUCTION TO SIMPLE ANALYSIS METHODS FOR: PAINTED SURFACES (PART 1 OF 1)

Mrs. Emilia Zambri, MSoc Sci Tangible Heritage Conservation.

PREFACE

Welcome to this series of techniques for managing change and assessing the condition of architectural heritage structures and historic heritage fabric. This newsletter aims to provide professionals, including Heritage Consultants, Architects, Archaeologists, and Conservators, with practical and effective methods to determine the most appropriate approaches to management, conservation, and restoration.

Inspired by the challenges encountered in safeguarding historic heritage, especially in under-resourced areas, particularly in Africa, this series has been developed to assist colleagues globally. The goal is to present simple and easy-to-use frameworks, case studies, and tests that can be employed to evaluate the preservation, conservation, and restoration needs of historic heritage, ensuring their safeguarding for future generations.

By utilising these techniques, the objective is to empower heritage professionals with the knowledge and tools necessary to make informed decisions about the preservation of our shared cultural heritage. Join us as we embark on a journey to protect and preserve the historical structures that define our shared identity.

1. THE LIMITATIONS OF PAINT SCRAPING IN THE TREATMENT OF HISTORIC SITES

The use of paint scraping as a method in the treatment of historic buildings and monuments is a widely adopted technique, however, its validity has come under scrutiny due to the development of more precise investigation methods. The paint scrape reporting process is limited by the absence of professional qualifications and the potential for subjective results, as the technique can be executed by individuals without any particular expertise or training.

With this said, it is a common misconception that the display of historic settings and contents is an objective representation of the past. Despite comprehensive research and high standards of presentation, subjectivity can still influence the outcome, particularly in paint scrape analysis. This undermines the authenticity of the depicted historical context.

2.??THE ANALYSIS OF PAINTED SURFACES IN HISTORIC BUILDINGS: OBJECTIVES AND CONSIDERATIONS

2.1. PURPOSE ONE: UNDERSTANDING HISTORICAL APPEARANCE

The first objective of analyzing painted surfaces in historic buildings is to gain insight into the appearance of a room or building in the past. This includes identifying the colors of paint schemes and special treatments such as gilding, graining, or marbling. With a knowledge of paint and pigment development, specialists can estimate the date of individual paint layers. This type of analysis has traditionally been performed on prestigious buildings, but it can also be applied to a wider range of buildings where there is less information and fewer records.

2.1. PURPOSE TWO: ARCHAEOLOGICAL AND DATING INFORMATION

The second purpose of paint analysis is to provide archaeological and dating information about a building's structure. Paint analysis can be used in conjunction with architectural research to determine changes made to a building over time, such as the location of filled-in doors or windows, or the approximate date of new flooring or extensions. Before conducting the investigation, it is important to conduct documentary research to identify areas that have been altered and to determine what questions can be answered through analysis.

2.3. IMPLICATIONS OF USING PAINT ANALYSIS OF DECORATIVE PURPOSES

While some individuals may use paint analysis as a guide for creating a new decorative scheme, it is important to note that the results may not always be clear. The reasoning behind the decisions is not always evident, leaving room for assumptions to be made. When using paint analysis for decorative purposes, it is important to make clear that the authenticity of the new scheme is not being claimed.

3. PAINT ANALYSIS TECHNIQUES FOR HERITAGE MONUMENTS AND BUILDINGS

The examination of paint layers in heritage monuments and buildings is a critical step in preserving the integrity of these structures. A thorough analysis requires the collection of a significant number of paint samples, which are then carefully polished and examined under a microscope. This process provides valuable information about the composition of the paint, the techniques used, and the overall structural integrity of the paint layers.

3.1.??THE PAINT ANALYSIS METHODOLOGY

Paint Analysis will invariably consist of at least three processes, The sequence will be roughly as follows:

1) The taking of paint samples and the making of cross sections...these will then be drawn or photographed

2) With the stratigraphy of the cross section made clear by a drawing, or photomicrograph, a scrape will then be made. The scrape must then be exposed to UV light for a period of time in order to clean up the colour

3) Pigment and media identification will be carried out with the aid of a number of microscopical, and microchemical techniques

4) The evaluation of the cleaned-up colour may be made by comparison with trial batches made up using the identified pigments

The procedure will result in the submission of a written report with drawings, photographs, and technical data on the materials discovered. There is no doubt that the analysis of a painted scheme is a lengthy procedure, but one that can do far more than reveal the colour of an earlier scheme. Indeed, very often an approximate date to each of the surviving layers can be given. As a result, the work of a particular architect or designer can sometimes be identified. Equally, if appropriate, the scheme that existed when the room was occupied by an historic figure can be established, and an accurate restoration to an earlier period attempted.

3.1.1. SAMPLE COLLECTION

The number of paint samples needed depends on the complexity and known history of the room being examined. In some cases, up to 100 samples, each measuring approximately half an centimetre, may be needed to accurately represent the paint layers. The location of each sample is recorded and numbered for easy identification, and the samples are set in clear polyester resin to prevent fragility and brittleness.

3.1.2. POLISHING THE SAMPLES

The resin-held paint chip is then sawn in half and smoothed down with a series of fine abrasive papers. The goal is to present a smooth, unscratched, and optically clear surface for examination under a microscope. The samples taken from wood and plaster should still be attached to a fragment of the substrate, while those taken from ironwork may show mill-scale or shiny metal flakes if taken correctly.

3.1.3. IDENTIFYING PAINT LAYERS

The next step is to determine which coat of paint was used as the primer, undercoat, and finish coat. In some cases, this may be straightforward, but it can be difficult to determine the exact number of paint schemes involved, especially when multiple schemes of the same color are used in succession. Carefully selected stains can be used to differentiate the layers.

3.1.4. ASSESSING STRUCTURAL INTEGRITY

The examination of the paint samples also provides insight into the structural integrity of the paint layers. The adhesion of each layer to the wall and the inter-coat adhesion can be gauged by analyzing the composition of each layer. Insurance companies may initiate an investigation due to accusations of poor workmanship, especially if paint has begun to peel off the walls of older buildings. Overpainting, poor preparation, and the weight of multiple coats of paint can all contribute to this issue.

The preparation and analysis of multi-layered paint samples and their structural integrity is standard practice for the examination of painted surfaces of heritage monuments and buildings. Mounted cross sections are used to investigate the materials, morphology, and stratigraphy of painted surfaces. The samples can provide information about the painting's layered structure, pigments, painting techniques, and any indications of overpainting or restoration.

3.1.5. EXAMINING THE SAMPLES

Tiny samples are embedded in a medium to preserve their position and layers for examination. The mounted sample is then polished and examined under a microscope to gather information about the paint's composition and techniques. This process helps to ensure the preservation and restoration of important historical structures and monuments.

3.2.??UNCOVERING PAINT LAYERS OF COLOUR EVALUATION

To accurately identify the color of each paint layer, it is necessary to first create a cross section of the paint layers. The process of uncovering the layers can be achieved through the use of a combination of solvents and mechanical abrasion, with guidance provided by a drawing or photograph of the stratigraphy.

The conventional method of exposing earlier layers through manual scraping with a scalpel is not only slow but also lacks precision. A more efficient method is to create a small crater using a knife, followed by sanding of the edges to form a gradual slope, resulting in a full sequence of paint coats that resemble a bull's-eye.

3.3.?PIGMENT ANALYSIS

3.3.1.?THE ANALYSIS OF PAINT LAYERS

The third stage of the process involves the examination of key paint layers to determine the composition of their individual pigment particles. By identifying these particles, specialists such as architects, archaeologists, and conservators can gather information on the age, color, finish, and intended purpose of a specific layer. This analysis is typically performed using a polarizing microscope (PM), but in some cases, a scanning electron microscope (SEM) may be utilized to confirm or deny the presence of specific elements. For example, the detection of Titanium would suggest that a paint layer was likely applied after the 1920s.

3.3.2.?IDENTIFYING PAINT CONSTIUENTS

Through the use of these instruments, the appearance of an olive green paint scheme, resulting from multiple layers, could be shown to only contain Prussian blue that has been impacted by the alkaline nature of the underlying plaster. This in-depth analysis provides a more thorough understanding of the paint layers, which is important in informing safe and effective conservation and restoration methods for historic buildings and monuments.

4.?LIMITATIONS

The use of "scrapes" as a method for determining original paint colors in historic buildings is unreliable and should not be relied upon. This technique, which involves using a penknife to scrape off layers of paint, is often performed by individuals without proper training and can result in incorrect conclusions about the original color scheme.

One issue with relying on scrapes is that it is difficult to determine the number of layers and their corresponding colors, leading to confusion and misinterpretation. Additionally, scrapes only show the current color of the paint and not the original color, as the oil medium used in early paint can yellow over time, distorting the true color.

Furthermore, the results obtained from scraping may not accurately reflect the original colors, as the colors may appear dull or drab before being exposed to ultra-violet light to remove the yellowing effect of the oil medium. The exposure to UV light can reveal brighter colors than originally thought.

The authenticity of paint analysis can be verified by requesting to see the report of the analysis, but it is concerning that many historic buildings still rely on unreliable techniques, such as scrapes, rather than more rigorous methods. There is a need for more professional and scientifically accurate methods to be utilized in order to properly preserve and present the historical colors of these buildings to the public.

5.?CONCLUSION

In conclusion, the series of techniques presented in this document has been developed for professionals in the heritage field to evaluate the condition of aged building materials and determine appropriate conservation and restoration methods. The series is aimed at providing assistance to under-resourced areas around the world and presents simple and practical tests to assess the conservation needs of architectural heritage. The limitations of paint scraping as a method for treatment of historic sites have been discussed, as well as the objectives and considerations of analyzing painted surfaces in historic buildings. Paint analysis techniques for heritage monuments and buildings have been presented, including the methodology and sample collection process. The procedure results in a written report with drawings, photographs, and technical data on the materials discovered, which can provide valuable information on the composition of the paint, techniques used, and overall structural integrity of the paint layers.