The Past Was Not Sepia-tone: Learning with Fluorescence Microscopy

An analysis of how paint analysis, including fluorescence microscopy, can alter our understanding of a building’s history.

The Maryland State House as it would have appeared from State Circle during the War of 1812. Image of Malcolm Dax
The Maryland State House Dome as the British would have seen it until at least the War of 1812

The Maryland State House Dome project provides an ideal opportunity to look at how the evolution of paint analysis including fluorescence microscopy and protein staining can help us understand far more than what color our historic buildings were painted, in the process allowing us to date paint layers, and selectively strip some coats while leaving others untouched. But this project also provides an outstanding example of the past was often far more colorful than the chaste shades of gray and sepia tone we imagine.

In studying an historic building to learn about its original form and the alterations, additions, and repairs that it has undergone, paint analysis can be a powerful tool to unlocking its secrets.

Cratering through the paint layers to get a first glimpse at the color history of the now white-painted dome. 2010 John Greenwalt Lee
Cratering through the paint layers to get a first glimpse at the color history of the now white-painted dome.

One of the earliest field methods for paint analysis was to sand a crater in the paint polishing to 600 grit with a little oil or mineral spirits. Visual examination of a paint chip can give some information. Use of a loupe at low power allows you to roughly estimate the number of layers and colors.

A tiny chip of paint cast in a clear resin and polished as a cross section can be viewed under a regular light microscope for even more detail.

Maryland State House Dome paint stratigraphy under uv light. Flourescence microscopy of Richard Wolbers, 2010
State House Dome paint stratigraphy under uv

With fluorescence microscopy you can not only determine the colors but distinguish each layer even when the same color has been applied multiple times and determine the type of coatings used (emulsion, oil, natural resin, latex etc.). Understanding the types and sequence of finishes can help in dating the coatings.

Additional staining methods, as well as SEM (scanning electron microscopy) and XRF (X-ray fluorescence) can help identify pigments which often will narrow the date range of use.

Knowing the composition of paint layers can also aid in diagnosing paint failure due to incompatibility.

massive paint failure and wood deterioration only a decade after previous restoration (and on an easily accessible landing used to hoist the flag every day). 2010
Hard to imagine such massive paint failure and wood deterioration only a decade after previous restoration (and on an easily accessible landing used to hoist the flag every day).

For the Maryland State House dome, incompatibility of modern latex paint over 17 layers of oil paints had caused much of the oil to fail and rapidly led to rotting of the wood at open joints. Up close, it was hard to believe the dome had been “restored” a decade earlier.

What would become even harder to understand however, was how the dome continues to be rendered in white and gray.

There is little need for guesswork about how best to strip paint, even to remove selected layers only, when starting with fluorescence microscopy.
Using a Recyclean vacuum system to remove the top layers of incompatible paint after softening them with a gelled paint stripper

When incompatible coatings cause layers beneath to separate and cleave, the microscopy can identify this so that a penetrating resin can be applied that will re-adhere them.  For the dome, we used B72 to ensure the edges of original paint were well-adhered wherever adjoining paint had failed back to wood.

We will explore the paint microscopy process in upcoming postings. For now let’s look at one recently completed project: restoration of the State House Dome where we were able to retain the vast majority of the paint history in place. The Maryland State House dates to 1779 and the current dome was completed in 1792 after storm damage to several earlier versions. This is the oldest continuously operating state house in the country and the Old Senate Chamber of the Maryland State House was where George Washington resigned his military commission in 1783 and, the following spring, where the Treaty of Paris was ratified, officially ending the Revolutionary War. At that time, Maryland’s State House was also functioning as the national capital. More on this history at Wikipedia.

Although restored less than a decade earlier, signs of failure on the dome were quick to show, even as viewed from the ground. As we prepared to restore the dome – which would require expensive scaffold access – we had to first determine the main cause of failure and decide where our efforts would be focused.

Balcony level view toward the Naval Academy showing a replacement copper ball for a missing unit.
Balcony level view from the dome showing a replacement copper railing cap that had been lost

We did this by taking samples where the dome sat on the flat roof of the State House and at the balcony level which exits from inside the dome 2/3rd of the way up. We concluded the main issue was paint incompatibility. The paint failure was largely the result of very heavy layers of latex being applied over 17 layers of oil. Latex is a fantastic way to strip earlier paints.

Paint stratigraphy under normal and UV light both before (above) and after removing the latex overburden. Richard Wolbers, 2010.
The thick layers of latex overburden (top) removed back to thin, stable oil layers

This is largely due to water moving through latex paints, causing them to expand and contract. This movement exploits weakened oil layers as it tugs at the surface. The installation of caulking was also trapping water in the wood shingles that had always been able to breathe, causing the shingles themselves to swell . Our main focus would be to remove the latex and get back into sound layers of oil paint, while re-establishing the original breathability of the dome system.

What we found in the process of looking for the physical evidence was that it also added to our understanding of the archival record. The paint evidence both confirmed contemporaneous annotations and added to our understanding of the involvement of an important artist in the dome’s expression. What was particularly compelling about our look at the paint history was finding that much of the dome had originally been painted a peachy-flesh tone that was over-coated with a golden glaze. It appeared the intended effect had been a golden dome – on the cheap since resources right after the Revolution were limited. In fact, although the original glaze used might not have held up for long, the golden appearance had been maintained – although in a single coat application of paint – two more times before the color scheme changed. Could it really be correct that the demure gray and white everyone was accustomed to was inaccurate?

Highlight from Charles Willson Peale sketch depicting "straw" as a key dome color.
Highlight from Charles Willson Peale sketch depicting “straw” as a key dome color.

Click to link to the Maryland State Archives for full detail of Charles Willson Peale sketch

Even more interesting was that where the color of the oval windows was not annotated we would find this detail was likely unsettled at the time as it appeared they were testing out color schemes of red versus blue in rapid succession because the earliest paint layers showed no sign of dirt deposition or weathering.

So was Peale present while color decisions were made??

Peale’s involvement in recording the paint treatments seen on the dome makes the manner in which the “straw” was achieved far more interesting. Most colors of this period were built up out of several hues and the peach tint that was used as a base for the glaze is the shade used for all female elements in art of the era (the solidity of men was expressed in grayish stone hues).

From peach to gold: How the early golden finish was achieved with a glaze
From peach to gold: How the early golden finish was achieved with a glaze

The State decided to stick with the Colonial Revival palette despite the more interesting historical paint evidence. Yet because we left all of the early oil paint intact and protected, it remains hidden beneath the white-painted slate and cedar shingles to inform the future, so no avenues are lost. (And given that the sprinklers on the exterior of the dome that expel every time there is a nearby lightning strike, leaking rusty water down the white-painted drum of slate at the oval windows, leaving an orange cast to this section, practicality may one day make the golden dome recreation more popular with the preservation community.)

The white-painted Maryland State House dome after restoration in 2010 is now stained from rusty sprinkler pipes staining the white.
The white-painted dome of today

Never should we assume the past was sepia-toned as the earliest photographs of our ancestors have caused us to believe. Rather than think of them as an artist’s flight of fancy, the works of period artists can often help us to understand the interior and exterior palettes of the era. We hope this blend of archival and physical evidence informing our past has been a good introduction into what paint microscopy can tell us about our more colorful past.

There is a tendency on preservation projects to sample historic finishes and then obliterate them. To hope that having recorded this information will somehow inform the future is pure fantasy. Most organizations can not find a ten-year old report, let alone anything older. And most of the time they would not even think to search those earlier documents.  We must maintain the evidence in place if it is to inform the future – especially as our ability to analyze the remaining information expands with new means of analysis nearly every decade.

Rendering of original Maryland State House Dome colors as viewed from State Circle. Image by Malcolm Dax, 2010
Rendering by Malcolm Dax

The paint evidence on this project is fascinating for the curious, so it is unfortunate the polychrome history was not re-established for public interpretation. In upcoming posts we will show results from other projects that allowed full interpretation of the evidence, making seemingly “dumpy” little buildings that contractors might have felt they were “stuck with” into icons that everyone could appreciate.

Far from a simple color analysis tool, in future posts we will look further at how fluorescence microscopy can confirm or deny our suspicions, while providing great insight into the past. It can provide important information that helps design and guide the treatment process.

Renderings of the early paint scheme for the Maryland State House Dome as viewed from the (modern) harbor. 2010 by Malcolm Dax
Renderings of the early paint scheme for the Maryland State House Dome as viewed from the (modern) harbor.