Glossary of Scientific and Technical Terms

Antwerp blue: a synthetic blue pigment composed of Prussian blue with alumina. We were not able to confirm the presence of Antwerp blue in our study and therefore 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: In a block, a stack of uniformly sized watercolor paper is compressed and sealed only around the edges with adhesive except for one small area at the top edge. After the top sheet has been painted, it can be separated from the block by inserting a sharp tool into the unsealed section and running it around the edges to cut the adhesive. Blocks made it easier to paint en plein aire by keeping the watercolor paper flat.

bone black: a black pigment formed from charred bone; 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 indicate a paper that has been repeatedly pressed between felts during the drying process. This pressing gives the texture a degree of smoothness between that of hot-pressed paper and 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) acetoarsenitee

Fiber Optic Reflectance Spectroscopy (UV-VIS or FORS): an analytical technique used to measure the reflectance of a material by 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 in pigments by their infrared absorption spectrum.

foxing: 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 indicate 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 also often used for black pigment formed from charred bone.

laid paper: also known as “laid and chain” paper. This paper is formed using a screen composed of thinly spaced wire, bamboo, or horsehair (which create the laid lines) held together with wire or thread (which create the chain lines). The screen does not allow the fibers of the paper to settle evenly; when laid paper is held to the light, a pattern of lines is visible.

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 light 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 it 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)e

quenching: any process which decreases the intensity of the fluorescence of a given substance

recto: (from the Latin) the front side of a piece of paper

reflected infrared image: a digital image obtained using light that contains infrared radiation in the 700–100nm range reflected off an object. This technique can allow differentiation between pigments, inks, and dyes.

rough: a designation used commercially to indicate 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 (pl. 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 fluorescent image: a digital image obtained using light that contains ultraviolet (UV) radiation in the 320–400nm range. UV light causes a visible fluorescence in many materials which can be used to differentiate pigments and dyes, among numerous other materials.

underdrawing: 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: (from the Latin) the back side of a piece of paper

viridian: a green synthetic pigment composed of hydrated chromium(III) oxide

watermark: 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.

wove paper: first manufactured in Europe in the second half of the seventeenth century. The paper is formed on a finely woven screen that allows the fibers to settle evenly; when wove paper is held to the light, no pattern of lines is visible.

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