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MCI 6278

Les Clochards, Montmartre Paris by Lois Mailou Jones

Smithsonian American Art Museum

Accession No. 2006.24.9

Technical Report  

 

Summarized by

Jia-sun Tsang, Senior Painting Conservator, MCI

Compiled by

Allison Martin, Paintings Conservation Intern, MCI

with

SEM and SEM-EDS: Judy A. Watson, Physical Scientist, MCI and Amber Kerr-Allison, SAAM ATR-FTIR and μFTIR by Jennifer Giaccai, Conservation Scientist, MCI

Microscopy by Melvin Wachowiak, Senior Conservator, MCI and Amber Kerr-Allison, SAAM

April 16, 2010

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Before treatment image in normal light of Les Clochards, Montmartre, Paris, casein on fiberboard panel, 1947, by Loïs Mailou Jones. SAAM Acc# 2006.24.9

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Executive Summary  Seven paint samples from the Loïs Mailou Jones’ Les Clochards, Montmartre Paris were brought to the Museum Conservation Institute for technical analysis at the request of Amber Kerr-Allison, Fellow in Paintings Conservation at the Smithsonian American Art Museum. The painting was undergoing conservation treatment and questions arose as to the surface coating and paint media. The aim of the project is to identify and better understand the surface coating and paint media of the painting. The requested actions were as follows: FTIR of untreated samples, microscopy of cross-section samples, and SEM-EDS of paint.

The FTIR analysis was effective in identifying the surface coating as shellac, however, the painting media was not able to be identified with any certainty. The paint layer does not have the characteristic appearance of oil paint and microscopy showed that the paint layer is thinly layered with the appearance of water-based media such as casein, protein, and gum. The dispersion of pigment particles, sedimentary layering on each other and their sharp distinct edges as seen in SEM support the possibility of a water-based media. As water-based media in general is lean, this would further explain the inconclusive results of the FTIR analysis.

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FILE INFORMATION

PROJECT TITLE: Paint and Coating Analysis- Loïs Mailou Jones’ Les Clochards, SAAM

PROJECT COORDINATOR: Jia-Sun Tsang, Senior Paintings Conservator, MCI

PAINTING TITLE: Les Clochards, Montmartre Paris

ARTIST: Loïs Mailou Jones

DATE: 1947

DIMENSIONS (H x W): 18 ¼” x 31 ¾”

MATERIALS/MEDIA: Casein on Fiberboard Panel

OWNER: Smithsonian American Art Museum

COLLECTION/ DEPARTMENT: Lunder Conservation Center, paintings

ACCESSION #: 2006.24.9

GEOGRAPHIC/CULTURAL PROVENIENCE: American

PROJECT MEMBERS: Jia-Sun Tsang MCI, Senior Paintings Conservator, Project Leader Allison Martin MCI, Paintings Conservation Intern Amber Kerr-Allison SAAM, Fellow in Paintings Conservation Anne Creager SAAM, Senior Paintings Conservator Melvin Wachowiak MCI, Senior Conservator, Light Microscopy Jennifer Giaccai MCI, Conservation Scientist, ATR-FTIR and µFTIR Judy Watson MCI, Physical Scientist, SEM and SEM-EDS

Table of Contents

Sampling .........................................................................................................................................5

Analytical Methods and Results ...................................................................................................8

I. Optical Microscopy ...................................................................................................................8

II. SEM and SEM-EDS ..............................................................................................................17

III. ATR-FTIR and µFTIR .........................................................................................................21

Discussion......................................................................................................................................30

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Sampling 

 

Sampling and Report by Amber Kerr-Allison

Sample/Material (if different from object):

Samples were taken from various locations on the painting. Diagram 1 denotes the physical location were the samples were taken, and the sample chart [Diagram 2] has been provided to indicate the type of sample ID location number, measured location of the sample, description of the sample, and any special notations to assist in technical analysis. Images and/or microphotographs have been included for visual references of the location and ID number of the sample. The labeled samples were encased between two glass microscopy slides for transportation and storage.

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Diagram 1 – Image depicts physical locations of sample numbers; descriptive details listed in Diagram 2.

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Diagram 2 – Descriptive details of samples taken.  

Sample Identification Chart  

             Artist:  Lois Mailou Jones (American, 1905‐1998)                     Title:  Les Clochards, Montmartre, Paris Date: 1947              Materials: casein on fiberboard panel (18 ¼ x 31 ¾ in.)           SAAM Acc# 2006.24.9 

 Samples taken by:  Amber Kerr‐Allison, SAAM/Lunder Conservation Fellow Date taken:  June 8, 2009 Sample technique:  Samples were taken using a miniature scalpel with a chisel chip; placed onto 25.4 x 76.2mm 1.2mm thick microscope slide in a circular well; then covered with 25mm x 75 mm clear glass microscope slide and secured using clear tape.  Sample numbers are written on each slide. 

 

Sample location ID# Location (measured upper right‐over then down) 

Description Reason for analysis & possible type of analysis 

Reference images 

1‐2006.24.9 (6 fragments) 

26 ½, 15 1/8 in. (see Diagram 1 for visual location) 

Sample taken from area of flaking.  Top layer is black, 

includes ground. 

Identification of medium used in paint and ground – FTIR, SEM‐EDS, cross‐

section analysis   Image of sample on glass slide, taken at 20X 

2‐2006.24.9 (scrapings from surface) 

25 ½, 10  in. (see Diagram 1 for visual location) 

Coating sample – scrapped from surface with possible inclusions of surface grime and paint.  Exhibited a waxy consistency during sampling, bluish‐white 

fluorescence under UV 

Identification of coating – cross‐section and FTIR 

analysis   Image of area coating sample was scrapped from, 

taken at 30X 

3‐2006.24.9 (4 fragments) 

25 ¾, 10 in. (see Diagram 1 for visual location) 

Sample taken from area of flaking in seated woman’s proper left hand.  Sample included paint 

layers and coating 

Identification of medium in paint and classification of coating – cross‐section 

analysis, FTIR   Image of sample on glass slide taken at 20X 

4‐2006.24.9 (5 fragments) 

19 ¼, 13 ½ in. (see Diagram 1 for visual location) 

Sample of a paint chip stuck to surface.  Sample fragmented during removal from surface, 

includes paint and possibly some coating.  Top color of sample is 

black. 

Identification of paint and coating – cross‐section and 

FTIR analysis   Image of sample on glass 

slide taken at 20X 5‐2006.24.9 

(fiber/pigment scrapings from surface) 

Lower right corner (see Diagram 1 for visual location) 

Fiberboard, dark pigment, and white ground samples  

PLM analysis at Lunder Conservation Center  No image taken 

6‐2006.24.9 (pigment scrapings of 

surface) 

31 ¾, 11 ½ in. (see Diagram 1 for visual location) 

Sample scrapings of top white layer of paint  FTIR analysis  No image taken 

7‐2006.24.9 (pigment scrapings of 

surface) 

25 in. from left  (see Diagram 1 for visual location) 

Sample scrapings of top grayish‐white layer of paint  FTIR analysis  No image taken 

8‐2006.24.9 (pigment scrapings of 

surface) 

3 ½ in. from left (see Diagram 1 for visual 

location) Sample scrapings of top yellow‐

white layer of paint  FTIR analysis  No image taken 

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Analytical Methods and Results

I. Optical Microscopy

Microscopy by Melvin Wachowiak, Senior Conservator, MCI with Amber Kerr-Allison, Fellow in Painting Conservation, SAAM

Report by Amber Kerr-Allison with consultation from Melvin Wachowiak

Background

Kerr-Allison removed samples from several areas of the painting, as indicated in Diagram 1. Samples were taken from areas of previous damage and along the edges of the painting. Samples of the coating had to be removed with a micro-spatula in order to shave off thin layers from the surface without damaging the paint surface beneath. Most of the samples provided for cross-section analysis contained multiple layers of paint, including ground and preparatory layers. Three of the samples included trace amounts of the surface coating. The paint samples were brittle, which caused many of the samples to fracture and fragment during the sampling process. However, this provided the opportunity for several analytical techniques to be performed on fragment samples from the same location, such as FTIR and SEM-EDS.

Sample inventory for optical microscopy:

1. A fragment from sample area #1-2006.24.9, from an area of paint loss at the base of the bench, near the seated woman’s skirt. The top layer of the sample is a dark-bluish black color with ground and preparatory/under-layer present.

2. A second fragment from sample area #1-2006.24.9, with similar layering.

3. A shaved fragment of the surface coating taken from sample area #2-2006.24.9.

4. A fragment from sample area # 4-2006.24.9, in an area of paint loss alongside the shoe of the seated male figure. Sample is of top black paint layer with a small amount of surface coating.

5. A second fragment from sample area # 4-2006.24.9 with top black paint layer and a small amount of surface coating.

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Methods

Embedding and Sample Preparation of Paints, Varnishes and other Coatings

Standard laboratory procedures were used to embed and polish samples for microscopy (details of the method and materials can be found in Efficient New Methods for Embedding Paint and Varnish Samples for Microscopy; Melvin J. Wachowiak Jr.; JAIC 43 (2004):205-226.)

Samples were positioned on pre-cast epoxy half-tablets and adhered using a small droplet of cyanoacrylate adhesive. Placement of the sample at the tip of the half-tablets assured proper orientation and location in the center of the embedment. The sample and half-tablet were then transferred into a silicon rubber mold for embedding. The epoxy resin, Tra-bond 2113 two-part system, was mixed and poured over the adhered sample and half-tablet. The liquid resin was held at room temperature for one hour, and then cured at approximately 45°C for 3 hours. Once de-molded, the tablets were trimmed with a high-speed diamond cutter to expose the sample. Up to four samples were fixed into aluminum holders. The rims of the holders are hard plastic and the face edge is parallel to the bottom. This leaves all tablet tips in the same plane and parallel to the bottom. Aluminum oxide abrasive films were used during the hand-polishing of the surfaces, with aliphatic hydrocarbon (Stoddard Solvent) as a lubricant.

Conditions for Brightfield, Darkfield and Fluorescence Microscopy

MCI has Leica models DMLM and DMRX research microscopes. Both share some components such as objectives and filters. The DMLM is a high quality laboratory microscope. The materials research microscope is capable of several reflected and transmitted light techniques, in sequence or simultaneously in some cases. The frame is designed for materials science applications (metallurgy etc.) so large heavy specimens can be placed on the stage. The translating stage can hold specimens several centimeters high, weighing more than one kilogram and can be rotated through 135̊.

The range of magnification for the reflected light techniques is 50x to 500x, measured at the eyepieces. Objectives are 5, 10, 20, 40, and 50x. Through the use of a prism system, Brightfield and darkfield illumination conditions can be alternated. The tungsten halogen lamp is the primary source of reflected light and it is corrected for daylight color temperature using a dichroic mirror.

The 5-20x brightfield/darkfield objectives can be used with and without coverglass on the specimen. Specimens are examined in both conditions. Typically, specimens are not affected by the use of low molecular weight aliphatic hydrocarbon (e.g. heptanes, ShellSolv, Stoddard Solvent) as the fluid under the coverglass. Specimens are also examined with and without transmitted light.

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The fluorescence illuminator is either a100W mercury or a 150W xenon lamp. The filters span the range from ultraviolet to the violet. The Leitz (Leica) filter sets characteristics are tabulated below:

Leitz filters for fluorescence microscopy (DMR and DMLM)

Filter system Excitation Excitation filter

Split mirror Suppression filter

Part no.

A UV BP 340-380 RPK 400 LP 430 513 804

D Violet BP 355-425 RPK 455 LP 460 513 805

BP = band pass filter

RKP = reflection short pass filter

LP = long pass filter

The DMRX is also equipped for reflected differential interference contrast (DIC) microscopy.

The range of magnification for the transmitted light techniques is 25x to 500x, measured at the eyepieces. Objectives are 2.5x, 5, 10, 20, 40, and 50x. The tungsten halogen lamp is normally the only source of transmitted light and it is corrected for daylight color temperature using a dichroic mirror.

A purpose-built digital camera is used for image acquisition (camera chip dimensions, as well as pixel count, determine ultimate magnification of image). The camera system is a Nikon DMX 1200 24-bit color system. The camera uses the Sony ICX085AK color CCD and Nikon’s proprietary Inter Pixel Stepping (IPS) high-density imaging technology. Color image capture is at resolutions up to 12 million (3,840 x 3,072) output pixels, in tiff, jpg, or bmp format. The Windows based system uses a PCI card for camera control. Resolution can be varied from native 1.4-mega pixels to the 12-mega pixels IPS format. Image information such as calibrated scales can be included with the image. Images are normally captured as 24-bit 1.4Mp tif images, approximately 3.8 Mp each.

Sample Cross-section Discussion

The samples removed for analysis by Kerr-Allison were divided for organic/inorganic analysis and light microscopy. Five fragment samples were embedded in epoxy resin and polished cross-sections were made for optical microscopy. Samples 1, 2, 4 and 5 contained casein paint, with a white ground and dark preparatory/under-painting layer visible in samples 1, 2, and 5, and only the top layer of dark paint was visible in sample 4. Samples 4 and 5 contained a fractional amount of the surface coating, while sample 3 was too small to provide any viable analysis of the surface coating using optical microscopy.

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SAMPLE DESCRIPTION: Most samples contained paint layers with some ground present. Three samples contained fragments of the surface coating, though one was too small for analysis using optical microscopy. All samples were provided to MCI encased between two glass microscopy slides which were sealed with tape. Some of the samples were in fragments due to the brittle nature of the casein paint during sample.

ANALYSIS: Several images of microscopy samples 1, 2, 4 and 5 were chosen to illustrate the most important observations. All images are appended as an Adobe Acrobat pdf; original images are kept in the MCI 6278 file. Samples 2, 4, and 5 were re-used for SEM-EDS analysis.

Sample 1. 

Brightfield illumination at 200x.  This sample was taken along the bottom of the bench near the seated female.  Two layers of paint applied above a white ground are visible in the sample, with another dark layer of paint below the ground layer.  This bottom layer is located just beneath the cast‐resin surface.  The comparative thickness of the white ground to that of the upper paint layers suggests it may have been used to paint‐out the remnants of a previous image, evident by the dark bottom layer of paint. 

 

   

Reflected darkfield with transmitted light at 200x.  The two top paint layers are more distinct in this image, which shows a thin dark pigment layer applied over a slightly thicker grayish‐black layer.  The pigment particles are well ground and uniformly mixed, with the layers evenly applied and level.  The white ground is an amalgam of fine to medium sized particles applied in a thick, even layer.  The bottom most layer of paint appears to have finely sized particles of a dark‐colored pigment with an uneven surface upon which the ground is applied.   

   

Ultraviolet light at 200x.  Violet excitation Leitz A filter used.  The white spherical shapes in the resin are entrained air bubbles.  The white ground layer fluoresces slightly, while the paint layer seems to absorb the UV light.  Organic materials routinely fluoresce, inorganic pigments tend not to.  What is more distinct in this image is the presence of a white (possibly ground) layer beneath the bottom paint layer.  This may support the existence of a previous painting that was covered over by the artist during the creation of Les Clochards.   

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Sample 2. 

Brightfield illumination at 200X.  Several thinly applied layers of paint are visible above a thick layer of white ground in the center.  The ground layer is applied over a thin layer of dark paint, visible along the bottom of the sample.  This fragment came from an area closer to the seated female’s skirt, which may account for the greater number of colored paint layers. 

 

   

Reflected darkfield with transmitted light, 200X.  This image shows greater detail in the layering structure for the upper paint layers; indicating that the pigment size, distribution, and application are similar to those in sample 1, but that the colors are varied and in some places intermixed.  The ground layer and bottom‐most paint layer remain consistent.   

 

   

Ultraviolet light at 200X. Violet excitation Leitz A filter used.  Organic materials routinely fluoresce, inorganic pigments tend not to. The white spherical shapes in the resin are entrained air bubbles.   

 

   

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Ultraviolet light at 400X.  This detail enhances the sparkling particles visible in the upper layers of white paint interspersed between the grayish‐black and dark‐blue paint layers.  This phenomenon is associated with zinc white pigment, which characteristically “sparkles” when viewed under UV light.  The remaining paint layers are likely comprised of inorganic pigments, due to their lack of fluorescence.  The white colored ground has fluorescing particles within it, which suggests the presence of an organic‐based medium, or additive.   

   

   

   

Sample 4 

Brightfield illumination at 200X.  This sample is of the top paint layer(s), taken near the seated male’s foot.  It is comprised of a very thin black top layer over a thick, uneven layer of a finely ground, homogenous blend of grayish‐black pigment.  The large air pocket in the center of the specimen has white polishing grit entrapped within it. 

 

   

Reflected darkfield at 200X.   In this image the thin black layer appear to be almost pale gray, possible due to the reflectance quality of the paint.  The detail of the pigments in the thicker paint layer suggests an amalgam of fine particles.  The particles are well blended.   

 

   

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Reflected darkfield with transmitted light at 200X.  The thin top layer of dark paint is more visible in this image. 

 

   

Ultraviolet light at 200X.  Violet excitation Leitz A filter used.  Organic materials routinely fluoresce, inorganic pigments tend not to.   The lack of fluorescence in the pigment layers suggest they are comprised of inorganic particles.  What is of note is a slight fluorescence on the top layer in the upper right of the sample. 

 

   

Ultraviolet light at 400X.  This detail image shows a very thin layer of a coating at the center top edge of the sample.  The coating has a slightly yellowish‐orange fluorescence in the UV light, suggesting an organic‐based coating, such as a natural resin or shellac varnish. 

 

 

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Sample 5. 

Reflected darkfield with cover‐slip at 100x.  This sample is a fragment of material taken near the foot of the seated man.  It is similar in composition and appearance to that of sample 4, however it also includes what appears to be a thinly applied white ground layer, with brown and blue pigments visible above the ground in the lower left of the image, a portion of brown pigment in the ground to the right of the image, and a thin layer of black pigment below the ground in the far right. 

 

   

Reflected darkfield with cover‐slip at 200x.  This detail shows the thick layer of grayish‐black paint with a discontinuous, thin layer of an amber‐colored coating visible along the top of the sample. 

 

   

Ultraviolet light at 200x. Violet excitation Leitz A filter used.  Organic materials routinely fluoresce, inorganic pigments tend not to.   The lack of fluorescence in the pigment layer suggests it is comprised of inorganic particles.  A slight fluorescence in material can be seen in the top thin layer of coating, in the white ground layer, and in the brown colored pigment at the bottom left. 

 

   

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Ultraviolet light at 400x.  This detail is of the thinly applied coating, visibly pooled between brush‐strokes or impasto in the top paint layer.  The surface coating exhibits a yellowish‐orange fluorescence; indicative of an organic‐based coating, such as a natural resin or shellac varnish. 

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II. SEM and SEM-EDS Analysis by Judy Watson, Physical Scientist, MCI with Amber Kerr-Allison, Fellow in Paintings Conservation, SAAM

Report assembled by Jia- sun Tsang, Senior Paintings Conservator in consultation with Amber Kerr-Allison  

Background

Scanning electron microscopy with energy dispersive spectrometry (SEM-EDS) works by sending a focused beam of electrons at a sample and measuring the energy of the x-rays emitted by the excited area of the sample. The emitted x-rays provide information about the elements present, and in some cases about elemental abundance. Previously this type of analysis has required destructive sampling, embedding, polishing, carbon coating, and analysis under high vacuum. The development of low vacuum (“environmental” or variable pressure) SEM, specially adapted detectors, and larger sample chambers has allowed the introduction of whole objects (up to 30 cm. in diameter and 8 cm high) into the chamber of the SEM for imaging and analysis without being altered.

For imaging, SEM provides two options. The first makes use of secondary electrons, which are generated near the surface of a sample when it is excited by the electron beam. Secondary electron imaging therefore provides good topographic information. The other type of imaging uses backscattered electrons, which come from deeper within a sample and provide information about the elemental composition of a sample, as heavier elements appear brighter than lighter ones. Backscatter imaging therefore offers not only morphological information about a sample, but also information about compositional differences within a sample.

Instrumental parameters for SEM analysis

The samples were imaged and analyzed using a Hitachi S3700-N scanning electron microscope and a Bruker XFlash energy dispersive spectrometer with Quantax 400 software. The sample was mounted on double sided carbon adhesive tape onto a carbon planchette; carbon coating was not necessary as carbon dust from the planchette was distributed over the entire surface of the sample while attempting to transfer the sample from the scalpel to the planchette. Samples were analyzed at approximately a 10 mm working distance, 15 kV accelerating voltage, at 150 Pa of pressure.

 

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Results

Sample 2 was analyzed by SEM-EDS. Thinly applied layers of the grayish-black and dark-blue paint layers are above a thick layer of white ground (Figure 1, right). This fragment came from an area closer to the seated female’s skirt.

Figure 1 SEM-EDS (left) and optical microscopy image (right) of paint sample 2 in cross-section, oriented with the ground on the bottom.

The hyper map (Figure 1, left) shows elements present in paint sample 2. Each element was assigned a specific color. Due to the density of different points of color present in any given area and intermixed nature of the fine pigment particles, it is difficult to extract, visually and clearly, individual element colors from the composite colors for the purpose of pigment identification. Thus, it is problematic to affirm with certainty the chemical compositions of the pigments from this form of data presentation. However, the thin zone of blue lying immediately above the ground appears to have a high concentration of zinc, based on the color code. This corresponds to an area of the cross-section thought be zinc white pigment, which characteristically “sparkles” when viewed under UV light –see microphotograph of sample 2 under ultraviolet light at 400X.

A pigment particle and the ground layer (outlined in green and labeled above) were analyzed further with the EDS. The pigment particle occurs in a paint layer that is intermixed in the grayish-black and dark-blue layers above the white ground layer. The spectra for these appear in Figures 2 and 3.

Ground layer 

Paint layer 

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Figure 2 The spectrum for a pigment particle, outlined in Figure 1.   

Based on the spectrum in Figure 2, the pigment particle has a strong peak for barium. However, carbon, oxygen, sulfur and iron are also notable peaks in the analysis spot. Basing on the elemental profile and its real-life color, the particle is likely to be barium sulfate mixed with trace of iron. XRD analysis would need to be done to confirm the mineral composition.

Figure 3 The spectrum for the ground layer of the paint sample.

The ground (Figure 3) has a significant peak for calcium. There is titanium present as well carbon, oxygen, and silicon, sulfur, magnesium, and aluminum. These results suggest that the

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white ground is composed of calcium- and titanium-based white pigments, such as Titanium Oxide. XRD analysis would need to be done to confirm this.

As seen in the SEM hyper map image, as well as microscopy images, the fine dispersion of pigment particles, sedimentary layering on each other, and their sharp distinct edges support the possibility of a water-based media.

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III. ATR-FTIR and µFTIR Analysis and Report by Jennifer Giaccai, Conservation Scientist, MCI

Introduction

Infrared Spectroscopy Theory The bonds between the elements in a molecule absorb energy as they vibrate and rotate. Organic and organometallic molecules absorb energy in the form of infrared light in the mid-infrared region (wavelengths from 2.5-20 µm, frequencies between 4000-650 cm-1). Each bond will often have many infrared peaks, giving a complex infrared spectrum. Often the infrared spectrum of an unknown sample can be matched to a known reference materials. If the sample spectrum is not a good match for a reference spectrum, some of the peaks in the infrared spectrum may be able to be assigned to a general class of material. Peaks can be described by their position (cm-1 or wavenumber), shape (broad or sharp) and intensity (weak, medium or strong) in the spectrum.

Two measurement methods are generally used at MCI for infrared analysis, attenuated total reflection (ATR-FTIR) or transmission through an infrared microscope (µFTIR). The differences between reflection and transmission results in ATR-FTIR and µFTIR produce slightly different spectra for the same sample. When examining the spectra in this report, please note that ATR-FTIR shows stronger absorption at low wavenumbers and less absorption at high wavenumbers while µFTIR will show stronger absorption at high wavenumbers and less absorption at low wavenumbers for the same compound.

For more background on infrared spectroscopy please see Infrared Spectroscopy in Conservation Science.1

Materials and Methods

Infrared Spectroscopy Instrumentation Instrument: Thermo Nicolet 6700 Fourier transform infrared (FTIR) spectrometer

Resolution: 4 cm-1

Correction: no corrections are performed on the spectra unless noted in the text.

ATR-FTIR (Attenuated Total Reflectance)

Sampling accessory: Golden Gate ATR with KRS-5 coated diamond crystal, single bounce, 45º

                                                            1 Michele R. Derrick, Dusan Stulik and James M. Landry. Infrared Spectroscopy in Conservation Science.

Los Angeles: Getty Conservation Institute, 1999.

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Detector: DTGS

Number of scans: 128

µFTIR (Infrared Microscope)

Sampling accessory: Centaurus microscope using a diamond microcompression cell

Detector: MCT/A

Number of scans: 264

Samples All samples were removed by SAAM Conservation Fellow Amber Kerr-Allison. The following are covered in this report:

- Sample SAAM 2-2006.24.9, coating - Sample SAAM 3-2006.24.9, peach paint - Sample SAAM 4-2006.24.9, black paint - Sample SAAM 6-2006.24.9, gray-white paint - Sample SAAM 7-2006.24.9, gray-white paint - Sample SAAM 8-2006.24.9, pale yellow paint

Analytical Procedure Prior to analysis, all samples were examined under magnification. All samples were examined by µFTIR. Sample 4-2006.24.9 was also examined by ATR-FTIR.

Results and Discussion

Sample SAAM 2-2006.24.9, coating The infrared spectrum of the coating clearly shows shellac (Figure 4). The doublet at 1716/1738 cm-1 and the small peak at 1636 cm-1 are clear markers for shellac. The remainder of the spectrum does not contain any peaks other than those found in shellac. Small amounts of other resins could be present in the sample, with their infrared absorption peaks hidden by the large amount of shellac present in the coating.

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1041

1112

1174

1252

1375

1465

1638

1716

1731

2858

2931

3446

MCI6278 SAAM 2-2006.24.9 coating over light areas

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1.0

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bsor

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Figure 4: Infrared spectrum obtained from 2-2006.24.9. The coating appears to be all or mostly shellac.

Sample SAAM 3-2006.24.9, peach paint The primary component of the infrared spectrum is zinc stearate or palmitate, indicated by peaks at 1540, 1465 and 1398 cm-1 and likely also the source of the strong C-H bands between 2700 and 2800 cm-1 (Figure 5). Absorbance peaks at 1174, 1117 and 1085 cm-1 indicate the presence of barite in the paint. The peak at 1734 cm-1 could be due to the paint binder, but may also be a remnant of shellac from the coating that was applied over the peach paint, and had been mechanically removed from the sample. The peak at 1647 cm-1 could indicate the presence of a protein, but no other proteinaceous peaks are visible. The source of the absorbance at 1584 cm-1 is possibly due to a copper soap, however the lack of a blue cast to the paint suggests another compound may be the source of the absorbance at 1584 cm-1.

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108

511

17

1174

1398

1458

1541

159

4

1657

1734

2849

2918

350

1

MCI6278 SAAM 3-2006.24.9 peach paint picked off resin layer

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0.36A

bsor

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1000 1500 2000 2000 2500 3000 3500 Wavenumbers (cm-1)  

Figure 5: Infrared spectrum of 3-2006.24.9.

Three small, broad and noisy peaks could possibly be identified as due to protein, the peak at 1647, a shoulder on the zinc stearate peak at 1530, and small peak at 1240 cm-1. Unfortunately, the spectrum is dominated by the zinc stearate and barite components of the paint and no binder can be positively identified (Figure 6). Note that although zinc stearate can be formed in paintings from the combination of zinc white and an oil binder, it also is a regular additive to commercial paint products, regardless of paint binder.

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zinc

ste

arat

e

zinc

ste

arat

e

barit

eba

riteb

arite

prot

ein?

zinc

ste

arat

e

zinc

ste

arat

e

prot

ein?

zinc

ste

arat

e

159

4pr

otei

n?

shel

lac

zinc

ste

arat

e

MCI6278 SAAM 3-2006.24.9 peach paint picked off resin layer

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bs

*IPR00026 Casein, from bovine milk, Sigma, C-7078, PMA, tran

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Abs

1000 1500 2000 2000 2500 3000 3500 4000 Wavenumbers (cm-1)  

Figure 6: Infrared spectrum of 3-2006.24.9 and IRUG 2000 library spectrum of casein for comparison.

Sample SAAM 4-2006.24.9, black paint The black pigment absorbed too much infrared energy to give a spectrum using µFTIR. The ATR-FTIR spectrum had an extremely sloping baseline due to the high absorbance of the sample and was corrected for clarity in the figures (Figure 7). The group of peaks between 1200 and 900 cm-1 are typical of carbohydrates, and may be due either to a paint component or the source of carbon pigment (e.g. vine black or charcoal). The remaining peaks in the spectrum are not distinctive enough for a match, and can neither confirm nor rule out the presence of a protein binder.

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*IPR00026 Casein, from bovine milk, Sigma, C-7078, PMA, tran

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1.0A

bs

*MCI6278 4-2006.24.9 black paint ATR

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Abs

500 1000 1500 2000 2000 3000 4000 Wavenumbers (cm-1)  

Figure 7: Baseline corrected ATR-FTIR spectrum of 4-2006.24.9 and reference spectrum of casein from IRUG2000.

Sample SAAM 6-2006.24.9, gray-white paint As in sample 3, the paint contains both barite and zinc stearate (Figure 8). In this paint, barite is the predominant peaks in the sample, with smaller amounts of zinc stearate. The peak at 1746 cm-1 is most likely due to an oil component of the paint. As in sample 3, the peak at 1585 cm-1 could be due to a copper soap. There are no peaks present in the infrared spectrum which suggest the presence of a proteinaceous binder.

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titan

ium

?

barit

e

barit

eba

rite

barit

e

zinc

ste

arat

e

zinc

ste

arat

ezin

c st

eara

te

158

5

174

6

MCI6278 SAAM 6-2006.24.9 gray-white sidewalk, finely divided area of sample

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1000 1500 2000 2000 2500 3000 3500 4000 Wavenumbers (cm-1)

Figure 8: Infrared spectrum of 6-2006.24.9.

Sample SAAM 7-2006.24.9, gray-white paint As with all the other paints examined, sample 7 contains large barite peaks (Figure 9). The rise in background after 800 cm-1 could be indicative of, but can not confirm, the presence of titanium white. Although no zinc stearate peaks appear in this sample, the presence of a large peak at 1587 cm-1 suggests the presence of copper stearate; the small blue particles seen in the IR sample may be due to the presence of copper stearate. The large peak at 1710, and two additional peaks at 1380 and 1470 cm-1, suggest the presence of mastic. The large broad peak at 1650 cm-1 and the smaller peak at 1416 cm-1 are from the consolidant used when treating the painting, Aquazol 500.

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copp

er s

tear

ate?

barit

e

barit

eba

rite

barit

e

copp

er s

tear

ate?

Res

in +

aqu

azol

Aqu

azol

Res

in +

aqu

azol

+ c

oppe

r st

eara

te?

copp

er s

tear

ate

Aqu

azol

resi

n

ilmen

ite?

MCI6278 7-2006.24.9 gray-white area

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Abs

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1000 1500 2000 2000 2500 3000 3500 4000 Wavenumbers (cm-1)

Figure 9: Infrared spectrum of 7-2006.24.9

Sample SAAM 8-2006.24.9, pale yellow paint The infrared spectrum of the pale yellow paint is very similar to that seen in sample 7, the gray-white paint (Figure 10). Two peaks are absent, the peaks at 1650 and 1416 cm-1 from the Aquazol 500 consolidant.   

barit

e

barit

e

barit

e

resi

n

resi

n +

copp

er s

tear

ate

copp

er s

tear

ate

resi

n

MCI6278 SAAM 8-2006.24.9 pale yellow paint

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Abs

orba

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1000 1500 2000 2000 2500 3000 3500 4000 Wavenumbers (cm-1)  

Figure 10: Infrared spectrum of 8-2006.24.9

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Conclusion No clear signs of binder were identified in any of the paint samples. The presence of a casein binder could not be either proven or disproven. The amount of binder present in the paints appears to be very low, in addition, the presence of stearates, traces of resins, and barium sulfate obscured large sections of the infrared spectrum.

 

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Discussion

Microscopic analysis allowed the paint layer to be much more closely visualized. The surface coating could not be analyzed because it was only present in small fragments or not at all in the paint samples taken. In all samples, the white ground layer was about twice as thick as the paint layer, which was often composed of multiple fine layers of paint and there appeared to be a thin layer of paint below the white ground. The ultraviolet light images suggest that there may be zinc present in the paint layer due to its characteristic bright fluorescence. Ultraviolet light images also suggest inorganic compounds such as calcium carbonate with some organic compounds in the ground layer. SEM-EDS provided some information as to the composition of the paint and ground layers. From the elements present, the white ground layer is likely to be a mixture of zinc white, titanium oxide, and calcium carbonate or calcium sulfate. The high pigment-to-binder ratio is clear through the sharp and clear outlines of the pigment particles; it is especially noticeable in the top layers of sample 2. The finely dispersed and well packed pigments thinly layered and intermixed and with occasional cracks provide indication of a lean media. The SEM- EDS spectra also show that there is barium present, possibly indicative of a filler in the paint mixture. The presence of barium sulfate (barite) is noted from the FTIR result. However XRD would be necessary to confirm or disprove this, as well as all of the mineral identifications. The FTIR results for binding media were inconclusive. This may be due in part to the fact that the paint has a high pigment-to-binder ratio, which makes it difficult to achieve strong FTIR results because the amount of binder falls below the sensitivity and detection limit of the FTIR instrumentation. For example, FTIR results of Sample SAAM 6-2006.24.9, a gray-white paint, suggested that the paint contains both barite and zinc stearate, which are colorants. The peak at 1746 cm-1 is most likely due to an oil component of the paint. There are no peaks present in the infrared spectrum which suggest the presence of a proteinaceous binder in this sample. However, from the visual observation in combination with microscopic and SEM hyper map, the thinness of the paint applications and small, sharply edged paint particles suggest that the binder for the paint layer is a water based media. From studying the artist techniques and looking at the visual quality of the paint, it is likely the paint binder is a water-based material. According to Amber Kerr-Allison’s research, casein paint was one of the paint media used by Loïs Mailou Jones. Casein paint was introduced as a commercially prepared artists’ paint after World War II, a medium known as poster colors,

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school colors and mat water color in addition to the term tempera. While a shared characteristic was the ability to be thinned with water, this binding media may have included mixtures of gum and glue, starch and glue, glue and egg, egg and oil, egg, resin and oil, and so forth. This may explain the FTIR results for media. However, the FTIR analysis was useful to identify with certainty the coating of the painting as shellac.