Glossary of Conservation Terms

Alkali - A general term referring to any basic material (pH greater than 7). Historically, 'alkali' referred to hydroxides and carbonates of sodium and potassium. Alkalis act as fluxes in ceramics and glass production-enabling silica to melt at lower temperatures.

Augustine - Christian Saint and perhaps the Church's most celebrated and influential theologian. Born at Tagaste in Numidia in 354 A.D.

Anne - The mother of the Virgin Mary.

Benediction - A petition for blessing.

Beta radiography - An imaging technique that uses a diffuse electron energy source (a source plate composed of a thin acrylic sheet embedded with radioactive carbon-14) to produce an image on photographic film. The plate emits high-speed beta electrons as the carbon isotope decays. The beta particles have low energy and pass harmlessly through a work of art on paper to expose an image on photographic film depending on subtle differences in the paper thickness. This technique helps record clear high contrast images of watermarks.

Bishop - A Roman Catholic clergyman ranking above a priest. A bishop has the ability to ordain and confirm and typically governs over a diocese, a territorial area of administration.

Binding media - The (usually) liquid (egg, water, or oil) in which pigments are mixed to create paints.

Blaise - Christian martyr believed to have been bishop of Sebaste in Asian Minor early in the 4th century.

Bole - A fine colored clay applied to a work of art to support gold leaf. The extremely fine particle size allows the gold to be rubbed or burnished to create a bright metallic surface. Because the gold leaf is so thin it is somewhat transparent and its color is modified by the bole color. Red bole , the most common color, adds to it warmth.

Brown earth - Brown earth pigments (ochers, siennas, and umbers) containing silica, clay and a mixture of iron oxides along with small amounts of manganese dioxide.

Calcite - Calcite may appear as clear colorless crystals, or white or pale shades of color depending on impurities preset. Calcite has been gathered or mined since Paleolithic times. In the form of chalk, calcite was powdered for use as a ground, gesso or pigment and as an ingredient in the manufacture of plaster, mortar, and cement.

Carbon-14 dating - One of a variety of radioactive dating techniques used on organic materials that were once part of living plants or organisms. The amount of carbon-14, a radioactive isotope of carbon, contained in a sample is measured enabling the date the material died to be calculated. Carbon-14 is absorbed by living plants along with other carbon as CO2 during photosynthesis. This carbon-14 is transferred to living organisms through the food chain. Only living organisms take in carbon-14. Upon death, the carbon-14 levels diminish because the radioactive isotope is unstable. The date of death can be determined because carbon-14 decays at a known rate.

Cartoon - A preparatory drawing or design for a painting or fresco.

Champleve enamel - A type of enamel decoration in which the enamel is applied and fired in cells depressed into a metal background.

Chiaroscuro - The treatment of the light and dark parts of a painting.

Consolidation - The process used by conservators to reattach loose and flaking areas of paint with special adhesives worked beneath the paint.

Coptic - A word used to describe the work, language, or church of the Copts, members of a traditional Christian church which originated in Egypt.

Core - a temporary internal support used during working and/or firing to prevent slumping of ceramics. Organic cores burned out during firing. Other cores, such as clay, were removed mechanically.

Cuprorivaite - a copper-bearing compound and the major constituent of Egyptian blue.

Dendrochronology - An examination technique that uses the number and width of annual growth rings to date wood. The sequential variations in a tree's ring width correlate to the annual climatic conditions for its local geography. Measurement of 50-100 years of growth rings visible on an artwork is compared to master charts for a specific geographic zone to determine the active growing years for the tree before it was felled.

Destructive Optical Microscopy - An examination technique which uses complex optical microscopes to examine samples taken from an artwork at high magnifications using plane and cross polarizing light to identify components by cataloguing optical properties. Additional chemical tests are sometimes performed under the microscope to aid in identifications. Sample preparation can vary depending on the material, ranging from particle mounts taken from specific areas to cross-sections that show the structure or stratigraphy of a larger area. For instance, the layering sequence of paint and varnish can reveal much about the technique and history of a painting. Sometimes sections are embedded in plastic resin and polished to maximize the information gathered.

Donor - An individual who commissions an artwork for presentation to a church or other institution.

Efflorescence - A white powdery crust formed by extraneous salts evolving on the surface of an object as a result of water migration. Typical efflorescence on masonry surfaces occurs when moisture dissolves water-soluble salts, then seeps to the surface, where the water evaporates leaving a salt residue. In faience manufacture this refers to a glazing process in which the colored salts are mixed in the paste before fabrication. The salts rise to the surface during drying and form the glaze when the object is fired.

Egyptian blue - A synthetic inorganic pigment consisting of coarse, irregular particles and ranges in color from a powdery blue to a royal blue. It is composed of a double silicate of calcium and copper prepared by heating a mixture of silica, copper salts, calcite and sodium salts to 830 C. This forms a stable blue frit that usually contains some calcite and quartz as impurities. The Egyptians used Egyptian blue since the time of the pyramids as a pigment. It was also made into a paste to form objects in a technology similar to faience.

Faience - Earthenware decorated with opaque colored glazes.

Galena - A gray metallic-like mineral composed of lead sulfide. When crushed, it forms a black powder.

Gesso - A paste prepared with size or glue and spread upon a surface to fit it for painting or gilding.

Gilding - Decorating with thin gold overlay.

Glass - A solid usually containing silica. Glass is formed by combining silica with fluxes (soda or salts) and stabilizers (lime or calcium oxide), that melt upon heating and cool to form a non-crystalline solid. Glass in ancient Egypt is defined as a soda-lime-silicate, and was made with the same raw materials used in faience and frit production.

Gold leaf - A sheet of gold varying from four to five millionths of an inch in thickness that is used for gilding.

Gregory - Christian saint and one of the four Latin Fathers of the Church (along with Ambrose, Augustine, and Jerome).

Ground - The first layer of a painting applied to a wood panel or canvas. For wood panels the ground layer was generally a mixture of chalk and animal glue to create a smooth surface to paint upon. The ground on canvas paintings is often lead white, sometimes tinted various colors.

Gypsum - A soft, transparent, mineral composed of hydrated calcium sulfate. Historically gypsum was used for carvings and as a paint pigment or ground. Burnt gypsum is commonly known as plaster of Paris.

Huntite - A white mineral composed of magnesium calcium carbonate.

Hygrometer - An instrument for measuring humidity

Infilling - The process of filling in a loss with an easily shaped material such as wax or spackling to even the loss with the adjacent original surfaces.

Infrared reflectography - A photographic examination technique that captures the absorption and/or emission characteristics of reflected infrared radiation. This low energy light near the "red" band of visible light can penetrate some paintings to reveal the black preparatory drawing (underdrawing) that was often applied over the white ground (underlayer) in preparation for painting. The success of this technique is dependent on the structure of the painting and the composition of the materials used.

Lime - Lime is prepared by heating calcium (limestone, marble, chalk and shells) to 540 C - a process known as calcining. Lime is used in plaster, mortar, and cement to form durable aggregates. When calcium carbonate is heated, carbon dioxide is driven off leaving anhydrous calcium oxide or quicklime. When quicklime is soaked in water, it is changed to calcium hydroxide or slaked lime. Slaked lime that is dried and ground to a fine powder is called hydrated lime.

Maenad - A woman participant in the rites of the Greek god of wine, Dionysus.

Martyr - Someone who sacrifices his or her life or something of great value for the sake of a principle. Christian martyrs were put to death because they would not renounce their religious beliefs.

Microscopy - The investigation of the panel and its components with a microscope.

Non-destructive Optical Microscopy - An examination technique which uses a variety of devices, such as single lens magnifying glasses, head loupes and binocular microscopes, to examine an artwork's surface, enabling much more information to be documented. Examination using low magnification can reveal details of color, surface texture, tool marks, joints, repairs, wear, surface coatings, and corrosion that are not visible to the naked eye.

Orpiment - A soft, yellow mineral composed of arsenic trisulfide. Orpiment occurs naturally, often in association with realgar - a soft red mineral also used as a pigment. It ranges in color from a bright lemon yellow to orange.

Parchment - The skin of a sheep or goat prepared as a writing surface.

Peter - The leader of the twelve Apostles, the companions of Jesus.

Pigment - The (usually) powdered substance mixed with a binding media (egg, oil, or water) which gives paints their color.

Polychromed faience - Faience decorated by multicolored glazes that are inlaid or painted. Ground glaze, ground glass, efflorescent frits, and prefired elements were used for inlays.

Red ocher - Iron oxides, in hydrated and anhydrous forms, produce a wide variety of red shades ranging from light, bright red to a deep purplish red. They are natural, earth pigments- all are stable, permanent pigments with good tinting strength. Iron oxides generally provide the color in red ochers and siennas.

Relic - An object venerated because of its association with a saint or martyr.

Reliquary - A container or shrine in which sacred relics are kept.

Retouching - To alter a painting or sculpture in order to produce a more desirable appearance.

Sagger - a ceramic container used to hold objects being fired in a kiln to protect them from ash and debris that can ruin the glaze.

Saint - A figure officially recognized by the Roman Catholic Church for remarkable piety or virtue.

Satyr - From Greek and Roman mythology, a woodland god with features of both a man and a goat.

Scepter - A staff or baton used as an emblem of authority.

Scanning electron microscopy - An examination technique that allows conservators to see things at magnifications hundreds of times greater than the light microscope. Because the sample is viewed in a beam of electrons, rather than the visible light spectrum, it appears in shades of grey. The electron beam scans across the surface of a sample producing different energy signals. Electrons provide the magnified image of the surface. X-rays are also emitted, and the resulting energy spectrum energy emission is analyzed quantitatively to provide identifications and compositional data for each of the elements present in the material- a technique known as energy dispersive X-ray analysis (EDXA) or energy dispersive spectroscopy (EDS). Because this analysis operates using a vacuum all elements can be measured to some extent, although again detection limits can vary. Maps that show the distribution of the chemical elements across the sample surface can also be generated. Sometimes-small objects can be placed in the SEM, for examination of surface detail; however, results are less satisfactory for non-conductive materials. For many materials such as glass, ceramic or stone, small samples are removed and coated with a fine conductive layer of gold or carbon to enable examination.

Scribe - A copier of manuscripts.

Setter - An object used to support the faience in the kiln during firing to minimize disruption of the glaze. Setters are designed to have the smallest surface area in contact with the glazed object. Setter's marks or firing marks are disruptions in the glaze formed by setters.

Silica - a compound of silicon and oxygen which was obtained from sand, quartz or flint. Quartz was used to produce the whitest faience because it contains few impurities.

Slurry - faience paste that is thinned with water and used to join separately made faience components prior to firing or to create inlays or surface decoration.

Solubility - A way of describing the amount of a substance that will dissolve in a given amount of another substance.

Spackling - The process of applying spackle, a powder mixed with water to form a paste and used as a filler for cracks in a surface before painting.

Tempera - A process of painting in which egg or egg yolk is used as the binding media for colored pigments.

Thermoluminescence dating - An examination technique which measures the accumulated effects of cosmic radiation received by a ceramic over time which have been retained within the structure since it was fired during manufacture This radiation results from the decay of radioactive materials; some of the energy of this decay becomes trapped within crystalline imperfections or impurities as electron shifts. If heated again, the accumulated energy is released and the thermoluminescent clock starts anew. T measures the light emitted during experimental heating to about 500º C, which enables the date that the ceramic was last heated to be measured. The relative energy of the light emitted can also vary due to compositional differences, environmental factors such as radioactive soil and the life of the object such as exposure to radioactivity through x-rays in a museum context. For this reason we keep careful records of all radiography exposures to ceramics in our care

Triptych - A painting with three panels.

Turquoise - An opaque sky-blue semiprecious gemstone composed of a hydrated basic copper aluminum phosphate mineral. It has not been identified previously as a pigment in ancient Egypt, although it was carved for amulets and jewelry. It produces a powder weak in tone when ground.

Ultraviolet fluorescence microscopy - An examination technique which uses complex optical microscopes to examine samples taken from an artwork at high magnifications using ultraviolet light. Many materials are identified by their characteristic autofluorescence; however special dyes (fluorochromes) are sometimes used to cause some materials to fluoresce in specific ways. This technique is very useful for documenting the layering of paints, varnishes and coatings in a section, enabling original materials and restoration layers to be distinguished and characterized

Ultraviolet light fluorescence - An examination technique which utilizes the characteristic of some materials to "autofluoresce" by absorbing the incident ultraviolet light and reemitting the energy at a longer (lower energy) wavelength. The intensity and color of the emission differs for various materials and can change as a material ages. Autofluorescence can help to visually distinguish between different materials, for instance, restoration paint often fluoresces differently from original paint layers. Fluorescence can also help to characterize materials using their autofluorescent colors, for instance shellac exhibits a distinctive orange fluorescence and madder (an organic red pigment) fluoresces bright red. Ultraviolet or UV light contains the portion of the electromagnetic spectrum with wavelengths ranging from 400-15 nm that occurs radiation occurs just beyond the violet (high-energy) region of the visible spectrum. Fluorescent light examinations are typically conducted using long wave UV light (400-320 nm) produced by black light bulbs or low pressure mercury vapor lamps.

Varnish - A liquid preparation that is applied to a surface and allowed to dry forming a hard, lustrous, and typically transparent coating.

Vellum - A fine-grained lambskin, kidskin, or calfskin prepared for writing on.

Xero-radiography - A medical radiography technique formerly used to obtain mammograms. It has since proven useful in the study of ancient technology, particularly ceramics, because of its ability to enhance edge differences between masses rather than just documenting differences in radiodensity as does traditional x-radiography. Therefore, it enables us to see the way the clay has been built up and manipulated by the artist during construction.

X-radiography - An examination technique which uses x-rays (high-energy radiation with very short wavelengths -0.001 - 10 nm) to penetrate an artwork and expose photographic film. The depth of penetration depends on the material's density. X-rays are commonly used in museums to photograph density variations resulting from manufacture or restoration. For instance, a painting's structure can be better understood by showing the build-up of the pigments below the surface by virtue of their different densities. Repairs that are not apparent to the eye are often clearly visible in x-rays because of the differing densities of original materials versus restoration materials. X-rays also are used in analytical equipment (see x-ray diffraction and x-ray fluorescence) for the determination of molecular and elemental compositions.

X-ray diffraction (XRD) - An examination technique used to identify the components of a solid crystalline material using an x-ray beam with a specified energy. The beam is transmitted or reflected through a sample in the form of a single crystal or crushed powder that diffracts it at varying angles dependent on the crystalline structures represented in the sample. The pattern of the diffracted beam is analyzed and used to determine the arrangement of the atoms in the material and obtain measurements of the spaces between atoms. This atomic arrangement is specific to each crystalline compound often enabling precise identification

X-ray fluorescence (XRF) - Is a nondestructive analytical method used to qualitatively and/or quantitatively determine the element content of the materials.examined. An x-ray beam with a specific energy is generated by an x-ray tube. This beam excites the electrons causing them to momentarily jump to higher energy states. An energy burst characteristic for each element is emitted (fluorescence) when the electrons return to their original state. The x-ray spectrum emitted from each element has a unique set of energies that are related to the type and amount of atoms present in the sample. This energy emission is analyzed qualitatively to provide identifications of the elements present in the material. Quantitative analysis enables the composition of the material (the percentage of each reported element) to be determined. Detection limits vary depending on the instrument, sample matrix, and individual elements. Typically, for nondestructive XRF (operated in air rather than under vacuum) calcium is the lowest atomic number element that can be accurately measured.

Yellow ocher - A natural yellow earth mineral primarily composed of goethite (iron hydroxide) and clay. Yellow ochers occur naturally throughout the world and have been used as a pigment since prehistoric times.

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