To better understand Whistler’s watercolors from a technical and material perspective, Freer and Sackler conservators and scientists employed multiple imaging technologies to examine the artworks. Technologies used included ultraviolet-induced visible fluorescence photography (ultraviolet), reflected infrared photography (infrared), and computed radiography (x-ray). To use the comparative imaging tool, click on the icons in the image bar to toggle between ultraviolet, infrared, and x-ray views. Zoom in for closer comparison and inspection.
Ultraviolet-induced visible fluorescence image (UV): Yellow fluorescence indicates the use of zinc white. Although probably used overall, the fluorescence now appears localized due to quenching. The quenching is apparent when compared to fluorescence along the edges, where the frame rabbet protected from light exposure. The slight blue fluorescence of unpainted paper may indicate a gelatin size, giving the zinc fluorescence a greenish cast. Degraded paper around the edges appears dark brown.
Reflected infrared image (IR): Orange becomes lighter, indicating cadmium orange (FORS/XRF). Green scarf becomes significantly darker due to either Prussian blue (FTIR) or possibly emerald green.
Computed radiography (x-ray): Images were originally taken to look for watermarks in the paper. Since some pigments are opaque to x-rays and appear bright (white) in these images, their distribution in the watercolor is also revealed.
Paper/Support
On cold-pressed, wove paper.
Pigments
bone black, burnt sienna?, cadmium orange, cadmium sulfide, cerulean blue, emerald green, iron oxide red, Mars pigment?, Prussian blue, raw sienna?, strontium chromate, vermilion, yellow ocher?, zinc white
Antwerp blue: A synthetic blue pigment composed of Prussian blue with alumina. We were not able to confirm the presence of Antwerp blue in this study and so have used the term Prussian blue exclusively.
Blind stamp: An image, design or lettering that is formed by creating an impression in the paper. It is called “blind” when no color is used.
Block: Blocks make it easier to paint en plein aire by keeping watercolor paper flat. In a block, a stack of uniformly sized watercolor paper is attached together with glue and bound around most of its periphery. There is no binding and the papers are not attached to each other for a small (1-2 inch) run along one edge. This provides a location for the insertion of a knife to cut off the topmost paper after it has been used.
Bone black: A black pigment formed from charred bone. It was also called ivory black.
Cerulean blue: A synthetic blue pigment composed of cobalt (II) stannate.
Chrome yellow: A synthetic yellow pigment composed of lead chromate.
Cobalt blue: Blue pigment composed of cobalt (II) phosphate or cobalt (II) arsenate
Cold-pressed: A designation used commercially to indicates a paper that has been repeatedly pressed between felts during the drying process. This pressing smooths the surface giving a texture in between a hot-pressed and a rough paper.
Computed radiography (x-ray): An x-ray technique that captures an image on a phosphor plate instead of film. The plate is then read by a specialized scanner resulting in a digital image file.
Emerald green: A synthetic green pigment composed of copper(II)-acetoarsenite
Fiber optic reflectance spectroscopy (UV-VIS or FORS): An analytical technique used to measure the reflectance of a material, scanning incrementally over a range of wavelengths in the ultraviolet and visible region of the electromagnetic spectrum. This method can be used to identify some pigments.
Fourier transform infrared spectroscopy (FTIR): An analytical technique that is used to identify organics such as the cellulose in paper and minerals such as used in pigments by their infrared absorption spectrum.
Foxing: Foxing is a deterioration process that occurs in paper resulting in snowflake-shaped stains in the paper. The name comes from the fox-like, reddish-brown color of the stains.
Gelatin size: Sizing is a part of the papermaking process where a material, in this case gelatin, is added to coat the fibers of the paper. Gelatin sizing helps to improve the water-resistance of the paper while also allowing inks and pigments to sit on the surface instead of being absorbed.
Hot-pressed: A designation used commercially to indicates a paper that has been run through metal rollers to impart a smooth surface texture.
Indigo: A natural blue organic colorant that was available both as natural indigo and as synthetic indigo.
Ivory black: A black pigment formed from charred ivory. This term was often used for black pigment formed from charred bone.
Liquid chromatography - mass spectrometry with a diode array detector (HPLC-DAD-MS): An analytical technique used to identify organic pigments and dyes. A sample in solution is separated into its components, then its absorption in the ultraviolet and visible of each component is measured. Finally the mass of each component is measured.
Mars pigments: A term for synthetic iron oxide pigments
Mounted: Many works of art on paper are attached to a thicker board, called a mount, for safer handling, protection and ease in framing. The paper can be held to the mount with hinges along the edges or can be attached overall with adhesive on the verso of the art.
Prussian blue: A synthetic blue pigment composed of a ferric ferrocyanide (Fe4[Fe(CN)6]3 or iron(III) hexacyanoferrate(II)).
Quenching: Quenching refers to any process which decreases the intensity of the fluorescence of a given substance.
Recto: Based on a Latin term, recto is used to describe the front side of a piece of paper.
Reflected infrared image: A digital image obtained using light that contains infrared radiation in the 700-100 nm range reflected off an object. This technique can allow differentiation between pigments, inks and dyes.
Rough: A designation used commercially to indicates a paper that has been allowed to air-dry after formation. This paper retains a rough surface texture.
Scanning electron microscopy with Energy Dispersive Spectroscopy: (SEM-EDS) SEM is an analytical technique that uses a scanning beam of electrons to create a high magnification image of a sample. In EDS, excitation of a location of the sample with the electrons can cause the release of a characteristic x-ray (an x-ray with an energy and wavelength dependent on the material) that is used for identification of the chemical elements present at the location.
Spectrum (plural: spectra) an ordered distribution of a range of something. A mass spectrum is a distribution of masses of the components in a material; the visible spectrum refers to the wavelengths of visible light.
Ultraviolet-induced visible fluorescence image: A digital image obtained using light that contains ultraviolet (UV) radiation in the 320-400 nm range. UV light causes a visible fluorescence in many materials which can be used to differentiate pigments and dyes, among numerous other materials.
Underdrawing: An underdrawing is a sketch made by an artist to outline and plan his composition. It is typically drawn with pencil, chalk or charcoal and is usually painted over by the artist while completing the work. Many underdrawings can be clearly seen using reflected infrared light because carbon black pigments absorb infrared and appear darker than other media.
Vermilion: A synthetic red pigment composed of mercury sulfide. Mercury sulfide also occurs as the natural mineral cinnabar.
Verso: Based on a Latin term, verso is used to describe the back side of a piece of paper.
Viridian: A green synthetic pigment composed of hydrated chromium (III) oxide.
Watermark: a watermark is a design that is clearly visible when light is shining through the paper. The design is fashioned with wire which is attached to the papermaking mold. Wet paper pulp distributed in the mold settles more thinly on the wire, creating a more translucent area once the paper dries.
X-ray fluorescence spectroscopy (XRF): An analytical technique that uses the characteristic x-rays released from a material after excitation with x-rays to identify the chemical elements present.
Zinc white: a white pigment composed of zinc oxide.
