Science & Research
Viewing an object under ultraviolet light reveals discrepancies of surface layers. For paintings, UV light reveals differences in pigments and incongruities of how the surface layers were applied. Consequently UV light will show up any overpaint, or any inpaint, or any partial varnish removal, or any shenanigans with signatures.
Jennifer McGlinchay Sexton conducted a terrific workshop at the 2017 AIC Conference in Chicago this year, “Tools & Techniques for UV/Visible Fluorescence Documentation.“ Jennifer walked her participants through the proper set-up, safeguards, and systematic workflows necessary for viewing art objects under UV light. She also supplied step by step instructions on how to produce an accurate image of UV Fluorescence.
Since the workshop, I worked on 2 oil paintings. Both were unvarnished, both were heavily soiled with aged ambient grime, and both used a combination of fluorescent pigments.
Both paintings, as well, had no repairs, no overpaint, nor funny signatures. So their respective UV images “before treatment” and “after treatment” were essentially the same, with the “before” images being slightly duller due to the layer of grime.
ultra violet light
Look at how those pigments pop under UV light.
Despite the fact that my equipment was not up to par with Jennifer’s, these images impart information not visible in regular light. The UV images clearly reveal the cadmium yellows in the Church landscape and the madder reds in the Dock scene. Lead white is the obvious colorant of the snow for both the scenes. Cobalt blue anchors the sky and sea in the Dock scene. And the addition of zinc white pops in and out in both paintings, adding luminosity to the more opaque lead white.
What does the art conservator do with this information? Not a great deal more than a professional would do otherwise. But there are some valuable ‘heads up’s:
• Take caution with solubility. Zinc white does not have the same parameters as Lead white. Madders are delicate.
• Don’t mistake pigment fluorescence for overpaint.
• Dirt soils an unvarnished surface very differently than a varnished surface. Treatment can target the inorganics in grime without involving solvents.
TURNED OUT TO BE A PRETTY NICE DAY, AFTER ALL
This little panel painting on board is dirty, or was dirty.
Besides completely masking the design, the colors, and the details of this picture, the surface dirt has swapped the crisp March morning for a dour November afternoon.
The dirt is not just a layer that has settled on the paint surface. It is a complex interaction of carbon, hydrogen, oxygen, nitrogen, silicon, phosphorus, proteins, salts and minerals in an ionic dance with the pigments and the resins of the painting. These elements have been trading ions for years. So any agent used to clean the dirt away, necessarily changes the chemistry of the original material. That is why a Professional Conservator will choose a cleaning agent that can capture the dirt without pulling away essential compounds of the original pigments and binders. With the return of the original design, colors and details, comes the fresh frosty air of a March morning.
Clear Your Brow
Art Conservators are relaxing with fresher air these days. Thanks to Conservation scientists, like Chris Stavroudis and others, cleaning paint surfaces are moving away from heavy solvents to more user and environmentally friendly solutions. Chris conducted a Workshop on his Modular Cleaning Program at the St. Louis Art Museum this past month. Under an IMLS grant petitioned by the Missouri Botanical Garden and attended by many Missouri conservators, the Workshop offered a new, cleaner age of conservation.
Cleaning Soot From Painting Surface and Collateral Damage
Fireplace soot is a common yet insidious grime on the surface of an oil painting. If the painting has had a layer of varnish, removal of soot is easier. But if the varnish has aged and cracked, exposing the paint layers to the settling soot, removal is tricky.
In the example, a early 19th Century still life by Ella Sophonisba Hergesheimer, the soot is most clearly imbedded in the frame rabbet margins and the center paint damage. An aqueous solution with strong surfactant did not remove the soot satisfactorily. Besides, the layer of discolored varnish had to be removed as well. An acetone/xylene Carbopol gel worked effectively on the aged varnish, as well as the soot. The gel was cleared with an aqueous/surfactant solution that removed residual varnish and soot.
The tricky issue was that affecting the top layer of paint was unavoidable. Largely this was due to the chemical change of the surface paint layers in the years of exposure to the soot and to the air. It goes against a conservator’s conscience to jeopardize original paint, but in an effort to extend the life and aesthetic of the work, a compromise was reached.
The more vulnerable pigments, like the umbers and the lakes were cleared of the varnish and soot with the strong and quick acetone gel. As the debris indicates in the image to the right, the black soot came off, the amber/green varnish came off AND some of the top layer of damaged umber paint. The clearing left behind a canvas/ground/paint composite that could be safely consolidated and flattened. The color revived yet the overall tone and painterly details remained.
Watt Restoration March, 12. 2016
Portrait Paintings over Photographs
Study of Portrait of Jefferson Wilcoxson, by Amanda Petronella Austin
The portrait of Jefferson Wilcoxson demonstrates the marriage between photographs and painting in the late 19th Century. The nascent art of Photography quickly utilized the printed image as a template for a painting or drawing. The practice had a dubious reputation, as the photograph was considered less an artist’s tool and more an artist’s cheat-cheat.
The artist of the portrait of Jefferson Wilcoxson was Amanda Petronella Austin. She attended the art school at the University of Missouri in Columbia. She also traveled and studied painting and sculpture in France in the 1880s. Her uncle, Jefferson Wilcoxson, funded her artistic education and adventures. In Europe, Austin would have been exposed to the latest in innovations in both fine art and photography.
Photographic plates and prints were handcolored. Additionally, photo negative (and daguerreotypes) were being projected and developed onto enlarged surfaces. The enlarged surface, whether paper or canvas, had to be sensitized with a treated gelatin to receive the image. Once the enlarged surface is rinsed of its sensitizing chemicals, it would be left to dry.
On this printed ‘outline’, the artist could add color details and build the paint layers in the traditional way. The finished product is a painting but it is technically constructed on a photograph.
Most attempts at this process are unsuccessful as aesthetic pieces. The figures are stiff and ‘frozen’ with little atmospheric depth or modeling. Amanda Petronella Austin’s portrait of her uncle, Jefferson Wilcoxson, steps through the barrier between photograph and painting. Austin rendered her portrait with the suggestive strokes and modeling of a painter. She clearly picked up the form of the photograph, as the series of images above show. But she transformed the flat image of the photograph into a multi-dimensional figure in light and shadow.
The conservation issues were in line with other canvas paintings on photographs. The pigment layer is exceptionally thin. The sized canvas is coated with a glue ground that is thin but resilient. The processed image is part of the ground, bound into it. Austin applied charcoal in loose rendering and then added transparent coats of pigmented resin washes.
Cleaning the surface of dust and grime necessitated bringing up some of the sepia pigment, notably in the peripheral areas where the wash was thin and deteriorating. The areas of loss were filled and inpainted. The aging canvas was reinforced with a layer of Beva film and mylar. The canvas was then set in a modern commercial stretcher.