Historic paint analysis, or architectural paint research, is the scientific analysis of a broad range of architectural finishes, and is primarily used to determine the color and behavior of surface finishes at any given point in time. This helps us to understand the building's structural history and how its appearance has changed over time. Researchers may gather data for the history of the interior decoration of a building or room.
Historic paint analysis shares a common methodology with the conservation and restoration of paintings used to conserve and restore two- and three dimensional works of art. This involves the identification of components such as organic or inorganic pigments and dyes contained in the pigments. Historic paint analysis also identifies the pigments' media of suspension such as (water, oil, or latex and the paints' associated substrate. A variety of techniques are used to identify and analyze the pigment layers and finish exposure, including Finish Exposure, optical microscopy, fluorescent light microscopy, polarized light microscopy, and Fourier-transform infrared spectroscopy.
These methods are useful for dating purposes as well. Likewise, analyses are used to evaluate levels of risk arising from agents of deterioration that can affect paint loss, surface deterioration, interaction with newer materials, substrates, de-lamination, media and pigment deterioration, and alligatoring. With this information the conservation scientist or researcher of historic interiors can develop a better understanding of the chronology of the painted surface and make recommendations useful in restoring its appearance to a previous state while ensuring its longevity.
History Historic architectural paint analysis finds its roots in the early twentieth century in the United States. The historic preservation movement began in 1849 with the preservation of Mount Vernon, the home of George Washington. Early preservationists became interested in authenticity. They began to realize that paints and finishes which had survived were very important but may not have been the original, or most significant, finishes.
In the 1950s and 1960s, paint colours were investigated at Independence National Historical Park in Philadelphia by the architect Penelope Hartshorne Batcheler. Her pioneering efforts introduced the use of a stereo microscope to examine the 18th century paints used at Independence Hall. Batcheler also introduced the use of the Munsell color system for matching and referencing colours. Her landmark publication, Paint Color Research and Restoration, was the first publication concerning the analysis of historic architectural paints for determination of original colour. At the same time, in the United Kingdom, microscopy of paint samples was developed by Joyce Plesters of the National Gallery, London who worked mainly with easel paintings but also with samples from wall-paintings.Joyce Plesters, 'Cross-sections & Chemical Analysis of Paint Samples', Studies in Conservation, vol. 2 (1956), pp. 110-157.
In the 1960s and early 1970s, Morgan W. Phillips at the Society for the Preservation of New England Antiquities (SPNEA) became involved with historic paint and color analysis, at the Harrison Gray Otis House in Boston. At the same time, E. Blaine Cliver, historical architect, who had worked with Batcheler at the National Park Service in Philadelphia, with the National Trust for Historic Preservation in Washington, DC, and later at the Northeast Regional Office of the Park Service, became involved with historic paint analysis. He set up a laboratory in Building 28 of the former Boston Navy Yard.
In the early 1970s, Frank S. Welsh joined the National Institute of Standards and Technology in Philadelphia and began to study historic paints with Batcheler. Welsh introduced the use of the National Bureau of Standards Color Name Charts, (National Institute of Standards and Technology) for naming colours matched to the Munsell color system. Welsh introduced the term "paint analysis" into the lexicon of historic preservation.Welsh, Frank S. 'Paint & Color Restoration', The Old-House Journal, vol. 3, no. 8 (August, 1975), pp. 1, 8-9.
Sampling methods Historically, paint analysis was done on-site by carefully removing later paint layers to reveal a sequence of finishes down to the substrate, this method is commonly referred to as the scratch and match method. This was the methodology employed during the early restoration of finishes at Historic Williamsburg. Although this method is employed by a few practitioners, it is not common because of its inherent problems of misinterpretation and failure to address issues such as paint aging and discoloration.
Because finished analysis is performed under laboratory conditions, samples are collected in the field for later analysis and can be collected by the analyst or by ship to a client. The samples are labeled during the collection process. Typical information includes the sample number, building name, building location, name of the collector, date of collection, and specific data regarding the actual location of the sample.
According to David Arbogast's recommendations for sample collection, samples are typically collected in one of two types of packages. Manila coin envelopes are highly recommended. They have large flaps which should remain unsealed. There is virtually no possibility of the sample migrating from such an envelope. The other possibility is plastic resealable (Ziploc) bags which can be opened and reclosed at will. The only drawback to this type of package is that labeling can be difficult. The samples are collected using a sharp metal blade such as a scalpel". The sample need not be large at all as it is viewed through a microscope but should have all its paint layers well adhered to each other and to their respective substrates.Arbogast, D. (n.d.). Sample collection. Sample Collection - APA. Retrieved April 20, 2022, from https://www.paintanalysis.biz/sampling.html
When removing a paint sample, it is important to also remove a piece of the substrate to ensure the stratigraphy collected is complete. To identify different pigments, binders, and colors within historic architectural sites, "Experts use a combination of mechanical and chemical investigations to reveal the hidden layers, while a microscopy lab analysis of the layers and substrate is used to define original colors and finishes."Canning, J. (2022, January 20). "Five common types of historic paint analysis". John Canning & Co. Retrieved April 15, 2022, from https://johncanningco.com/blog/types-of-paint-analysis/
The traditional method of carrying out a "scrape" using a scalpel is a slow and very inaccurate method of exposing the earlier layers. The disadvantages of the former technique are that given the relatively low level of magnification it is easy to miss critical layers and to misidentify layers such as primed coats as being historic finish coats. Also, the variable light sources on site alter the perception of the colors to varying degrees. It is often more effective to make a small crater with a knife and then to sand the edges to a gradual slope, the paint layers widening as the surface is rubbed down. The finished result will look like a bulls-eye, or target, with the full sequence of coats revealed.Patrick Baty, 'To Scrape or Not to Scrape' for the drawbacks of carrying out a scrape, originally published in Traditional Paint News vol. 1, no. 2 (1996). In past and recent analysis, paint researchers have become increasingly aware that the samples removed from the site for study may not represent the true historic color.Perrault, C. L. (1978). Techniques Employed at the North Atlantic Historic Preservation Center for the Sampling and Analysis of Historic Architectural Paints and Finishes. Bulletin of the Association for Preservation Technology, 10(2), 6–46. https://doi.org/10.2307/1493611 Due to this inaccuracy in traditional sampling methods, architectural paint research had developed into material science.
Agents of deterioration Historic paint analysts rely on the chemical properties of pigments to correctly identify and date pigments within historical paint analysis. However, successful analysis of pigments may depend on physical, chemical, and biological deterioration. The top layer of substrate is more susceptible to biological and physical weather damage while lower layers are susceptible to chemical damage based on the microbial deterioration. In order for conservators to create a plan to identify and protect historic paint, they must understand how the agents of deterioration act.
Light Light deterioration causes oxidization and other degradation of the inorganic and organic pigment and media components of paints, as visible light can fade, bleach, or darken the surface and outer layers of paints.National Park Service (2016, January 12). "Chapter 4: Museum Collections Environment", in The Museum Handbook Part 1: Collections. National Park Service. Washington, DC. For external murals and buildings, air pollution can cause disintegration, discoloration, or corrode the paint murals and facades.
Chemical interaction Paints made with pigments dispersed in the medium of linseed oil can yellowing over an extended period of time. To prepare samples for analysis this yellowing can be bleaching samples for two weeks under a fluorescent tube. The colour of the sample can then measured with a chromameter. As well as an understanding of how colour and pigments age, the conservator or paint analyst will use their knowledge of historic architecture, building history, interior decoration, craft practices, architectural finishes and their materials and manufacture.Historic New England. (n.d.). Property care white papers. Historic New England. Retrieved May 1, 2022, from https://www.historicnewengland.org/preservation/for-professionals-students/property-care-white-papers/
Biodegradation Many elements in the natural environment can lead to the degradation of paint. Microorganisms, fungi and algae can degrade the pigments, binders and medium of suspension and substrate through their respiratory activities. Orio Ceferri cites these several factors: "...cyanobacteria and algae growing on paintings exposed to light, such as frescoes on the facades of buildings, may cause considerable damage. Besides the aesthetic damage caused by a green, black, brown, or yellow algal patina covering the painted portions, these organisms may cause weathering of the surface layers, accelerating detachment of portions of the painted layer as well as the underlying plaster".
Incorrect temperature Unsuitable temperatures can cause paint layers to crack and fractures can be seen in samples using an optical microscope. At low temperatures, "materials such as varnishes, lacquers, wood, oil, alkyd, and acrylic paints are especially at risk and need to be handled with extreme care". Similarly, incorrect relative humidity can break paint if the air is too dry, while high humidity can result in deformities, swelling, and mold can affect organic pigment samples. Consistent temperature and humidity fluctuations can affect the water content of the paint. These deformities may start as a small area of the paint layer but can quickly "increase in the surface area if left undetected".
Physical force Physical force can cause chips, cracks, and breaks in pigment layers from improper work handling. All staff and handlers should be trained on proper moving procedures when transporting artwork to prevent this mishandling.
Fire Fire will result in complete, irreversible damage to the pigment on any work of art or historic building. To prevent damage, organizations should have an Emergency Plan to determine the best course of action in case of a fire while also having the correct safety measure to prevent collections or building fires.
Vandalism