Overview

Historic paint analysis is the scientific identification of finishes applied to architectural features at some point in time identified as being historic. This might be the original construction, as is often the case, or some subsequent period in time, usually associated with the life of a historic person or a particular event (e.g. the signing of the Declaration of Independence). It is not limited to paint only, but includes a wide array of other finish types such as varnishes, shellacs, metallic leafs, etc.

Historic paint analysis can be used to determine a large amount of information regarding finishes. This includes information regarding surviving colors, original colors, sheen, lead content, finish type, media employed, pigments, application techniques, and weathering characteristics. Typically, however, color determination is the goal of the analysis. There is a common misunderstanding that the surviving color is exactly the same as the original color and that matching that color will result in a correct restoration. Unfortunately, this is infrequently the case. Most paints do change over time in the following ways:

• Fading. The more intense the pigment the more likely fading will be an issue. For example, certain red pigments will fade to the point where they disappear entirely. On the other hand, certain inorganic pigments, include some red pigments, are no affect by fading.
• Color shifting. Certain pigments will change color over time. For example, Prussian blue will change from an extremely strong green-blue to a softer and lighter blue within a relatively short time. One significant question that should be addressed in these cases is whether the original design intent was for the initial color or the shifted color.
• Yellowing. Linseed oil, among several media, will yellow over time, shifting the color toward the yellow end of the spectrum. This is particularly marked in white paints resulting in the question as to whether the color should be restored to an originally bright white or to an aged, mellower appearance
• Chalking. Lead based paints were often formulated to chalk over time and thereby create a rough surface to which later paints would readily adhere. This change in sheen poses a dilemma in restoration because modern paint do not chalk, thereby leaving the choice to recreate a new, eggshell or glossy finish, or a flat finish resembling a chalked surface.

The purpose, then, in historic paint analysis, usually, is to recreate the original color and sheen of the historic finish in question. Typically, this is accomplished with modern materials and with modern methods. Therein lies the challenge.

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Paint Analysis

There are a number of methods which have been used for paint analysis. They can be roughly divided into two camps. Beginning in the early twentieth century paint analysis was conduced on site and typically involved scraping the various finish layers to reveal a sequence of layers to the substrate. Using a handheld magnifying glass a layer would be identified and color-matched. By the end of the twentieth century a second method had been developed and refined. This method entailed the collection of small samples of the finishes from the site which are then examined under a microscope and color-matched under uniform lighting conditions – sometimes natural north light and sometimes artificial north light.

The disadvantages of the former technique are that, given the relatively low level of magnification it 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.

The advantages of the latter technique are the opposite of the former technique with the result being that virtually all paint analysis today is conducted using the latter technique.

Following collection of the samples, they are examined in a laboratory environment. Some analysts choose to examine only a single layer or two, which they conclude match the requirements for the historic finish. I examine each and every layer and color-match opaque, pigmented layer to the Munsell System of Color, a standard color reference system used for paint anlaysis.

The Munsell System of Color is a scientific system in which colors have been ranged into a color fan based upon three attributes: hue or color, the chroma or color saturation, and the value or neutral lightness or darkness. Unlike color systems developed by paint manufacturers, the Munsell system provides an unchanging standard of reference which is unaffected by the marketplace and changing tastes in colors.

The hue notation, the color, indicates the relation of the sample to a visually equally spaced scale of 100 hues. There are 10 major hues, five principal and five intermediate within this scale. The hues are identified by initials indicating the central member of the group: red R, yellow-red YR, yellow Y, yellow-green YG, green G, blue-green BG, blue B, purple-blue PB, purple P, and red-purple R. The hues in each group are identified by the numbers 1 to 10. The most purplish of the red hues, 1 on the scale of 100, is designated as 1R, the most yellowish as 10R, and the central hue as 5R. The hue 10R can also be expressed as 10, 5Y as 25, and so forth if a notation of the hue as a number is desired.

Chroma indicates the degree of departure of a given hue from the neutral gray axis of the same value. It is the strength of saturation of color from neutral gray, written /0 to /14 or further for maximum color saturation.

Value, or lightness, makes up the neutral gray axis of the color wheel, ranging from black, number 1, to white at the top of the axis, number 10. A visual value can be approximated by the help of the neutral gray chips of the Rock or Soil Color chart with ten intervals. The color parameters can be expressed with figures semi-quantitatively as: hue, value/chroma (H, V/C). The color “medium red” should serve as an example for presentation with the three color attributes, 5R 5.5/6. This means that 5R is located in the middle of the red hue, 5.5 is the lightness of Munsell value near the middle between light and dark, and 6 is the degree of the Munsell chroma, or the color saturation, which is about in the middle of the saturation scale.

In addition to the microscopic identification of the finish layers, further testing can be undertaken for identification of elevations such as lead and other pigments. Although very rarely done, this additional information can prove to be very helpful.

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Report

Following laboratory analysis of the paint samples, a report is prepared providing a complete discussion of the findings. An introductory section provides and overview of the project and explanation of the process of paint analysis. Each sample is then discussed individually with commentary regarding things such as probable original finishes, their aging, their probable original characteristics, loss of finish layers, and other such information. A conclusions and recommendations section typically follows larger sets of samples and summarizes, coordinates, and compares the individual findings (hopefully) into a unified understanding of the finishes history of the building.

Typically, the report does not include Munsell chips, assuming that the client has access to them. However, this is not always the case. In these situations the client can either order the chips themselves or have myself order them. In the case where a modern paint manufacturer’s color system is proposed to be used for replicating historic colors, the colors determined to be historic can be matched to the manufacturer’s system with the caveat that the color match frequently varies considerable and that the manufacturer will change the colors in due time.

Also not typically included in a report is color microphotography of the paint samples. This is not recommended because the colors rendered in the photographs differ from those of the analysis because a halogen light source is used for the photography, which distorts the colors. In addition, the dyes used in the color prints are subject to fading and color shifting so that, in time, their differences from the original colors will be exacerbated. However, there are occasions where color microphotography is determined to be useful for illustrative purposes only.

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Exceptions and Rarities

Although historic paint analysis is used typically for historic buildings, it can, and has been employed, for a large number of projects outside the standard architectural milieu. These include painted furniture, archaeological sites involved artifacts with applied finishes, and other miscellaneous objects. It is not used for easel paintings and other painted art objects which employ artists’ paints. Analysis for art of this nature is best conducted by a professional art conservator.