Glossary

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- A -

Abrasion

Surface disruption caused by rubbing.

Acetate

In the photographic context, a transparent plastic base for photographic film made by treating cellulose with acetic acid. This term is used for various modifications of cellulose acetate, e.g., cellulose diacetate, cellulose triacetate, cellulose acetate propionate, and cellulose acetate butyrate

Acetate decay

Degradation of cellulose acetate film base that may cause distortion, shrinkage, and brittleness, often detected by a vinegar odor. The severity of decomposition can be determined using A-D Strips. (See also Vinegar Syndrome)

A-D Strips

Indicator papers, manufactured by IPI. The strips change color when acetic acid is produced by degrading cellulose acetate film base (See Vinegar syndrome).

 

- B -

Baryta

A layer of barium sulfate in gelatin applied to the surface of photographic paper base to provide opacity, smoothness, and brightness.

Base

The support of an imaging or recording material on which the recording layer is coated.

Binder

The transparent layer on the surface of a traditional photograph in which the image is suspended. For example, gelatin is the binder for silver image particles in photographic media.

Binder degradation

Decomposition of the polymer layer that contains the recording material. (See also Magnetic shedding)

Biological decay

Caused by the attack of biological organisms on objects and materials. Organic materials are particularly susceptible. Some examples are staining from mold growth and loss due to feeding by insects or their larvae.

Bleed (or Color Bleed)

The migration of of a colorant through or across the surface of a print.

Bleed-Through

The migration of a colorant through the print to the reverse side.

Blocking

The sticking together of materials due to physical contact.

Blur

Lack of image, character, or line sharpness.

Buckling

Distortion or lack of flatness. This may be caused by chemical degradation, shrinkage, or flow. (See Distortion.)

- C -

Catalytic Fade

The accelerated fading of one colorant caused by the presence of another colorant upon exposure to light.

Channeling

Buckling of the emulsion caused by base shrinkage.

Chroma

The divergence of a color of a given value from gray of the same value; sometimes referred to as “saturation.” One of the three main characteristics that describe a color (along with hue and value).

Chromogenic Print

Traditional color photographic print.

Cold Storage

A storage condition with temperatures usually under 45°F (7°C).

Chemical decay

A chemical reaction that causes changes in an object at the atomic and molecular level. Examples include metal corrosion, deterioration of pigments, staining by acidic materials, and embrittlement of pulp papers and textiles.

Color balance shift

A change in the overall tone of color images.

Color bleeding

Movement of the colorant in color images, laterally into adjacent areas in the image plane, through the base (often appearing on the verso of the sheet), or outside the image plane to a contacting sheet.

Color fading

A decrease in image density that results in an overall lightening of the image.

Color image decay

Can be manifested as color fading, color balance shift, yellowing, or color bleeding.

Composite materials

Materials made up of two or more materials. Individual materials will react with the environment in different ways, often in opposition to each other, setting up physical stress and causing chemical interactions that cause deterioration.

Cool Storage

A storage condition with temperatures usually between 45°F (7°C) and 60°F (16°C).

Crossed polarizers

Polarized sheets whose axes of transmission are oriented at right angles to each other for the purpose of depicting the orientation of polyester molecules. Bands of color appear when polyester support is placed between crossed polarizers.

- D -

Delamination

Separation of individual layers of a laminated material, e.g., separation of emulsion from the glass base in photographic plates or separation of individual layers in optical discs.

Dark Fade

Loss of colorant when a print is stored in the dark.

Dark Stability

The ability of a material to resist degradation when stored in the dark.

Dew point

A measure of the absolute amount of water in the air. As air is circulated into and around a building, its absolute moisture content—and therefore its dew point—does not change unless it is humidified or dehumidified. Dew point is the temperature at which water will begin to condense out of the air, expressed in degrees F or C.

Differential Gloss

Variation in gloss across the surface of a print.

Dimensional change metrics

Measures of the potential for physical change in an organic material caused by gain or loss of moisture.

- E -

Electrophotography

Printing process in which the image is formed by transfer of charged toner to paper and then fixed by heat, pressure, or evaporation.

EMC (Equilibrium moisture content)

The amount of moisture in a material at a certain relative humidity. An object equilibrates as it absorbs and releases moisture in an effort to reach a balance between its moisture content and that of the surrounding environment. (See Organic materials.)

Emulsion

The image-forming layer of photographic films, papers, and plates.

- F -

Fading

Loss of colorant resulting in image lightening or color shift.

Ferrotyping

A change in surface gloss due to intimate contact with another surface under high humidity.

Flaking

Localized separation of layers in a print.

Fogging

The generation of unwanted non-image density in non-reversal photographic materials or unwanted loss of image density in reversal photographic materials. This may be caused by exposure to radiation or chemicals, by aging, or by excessive or unwanted reactions during processing.

- G -

Gelatin

A protein obtained from naturally occurring collagen. Used as a binder for the image layer of photographic materials.

Gelatin Stain

The discoloration, usually to yellow, of the gelatin binder or ink receiver layer in traditional photographic and some digital printing papers.

Glass deterioration

Degradation of glass supports caused by exposure to high humidity. May result in a hazy appearance, formation of liquid droplets, or layer separation in photographic glass plates.

Gloss

Reflectivity of the print’s surface. Sometimes referred to as "sheen."

Gloss Defects

Loss or gain in the gloss of a print in discrete areas or over the entire surface of the print.
 

- H -

Harmful enclosure

A folder, envelope, sleeve, box, or other container that causes silver image decay and/or staining of binder and supports.

Hydrolysis

Chemical reaction between water and colorants, image layers, and/or papers resulting in their degradation. Acids, alkalies, and/or heat can accelerate these reactions.

- I -

I3A

The International Imaging Industry Association, which facilitates the development of media storage and other technical standards for the imaging industry.

Inorganic materials

Materials with a geological origin, which have undergone extreme pressure or heat, usually are not combustible at normal temperature, can react with the environment to change their chemical structure (corrosion or dissolution), and usually are not sensitive to light.

ISO

The International Organization for Standardization, in Geneva, Switzerland, which publishes international specifications, test methods, and best practices for a variety of industrial products and processes.

- L -

Layer separation

The partial or complete separation of a laminate into its constituent layers. (See also Delamination.)

Life expectancy (LE)

A rating for the expected longevity of recording materials and associated retrieval systems.

Light/UV Fade

Loss of colorants induced by light or UV radiation.

Lightfastness

Resistance of prints to change upon exposure to light or UV radiation.

Line Spread

Broadening of a printed line due to high-humidity-induced migration of colorants across the surface of the print.

 

- M -

Magnetic shedding

Degradation of the binder of magnetic tape, which results in loss of magnetic oxide particles during storage or playback.

Mechanical decay

A change in the physical structure of an object caused by changes in the environment (variation in and improper levels of temperature and relative humidity) that lead to stresses in an object. Examples include cracking and buckling of wood; warping, shattering, and cracking; and softening of plastics and waxes. Mechanical decay is also caused by force resulting in chipping, cracking, abrasion, distortion, etc.

Microspots

Small colored spots, usually red or orange, caused by localized oxidation of black-and-white images. Also known as red spots, redox blemishes, or measles.

Mold

Fungus that grows on polymer or organic materials exposed to high humidity; causes material degradation.

Mold risk factor (MRF)

A number derived from temperature and relative humidity data over a period of time which expresses the likelihood and severity of mold growth on susceptible collection materials.

Molecular sieve

A material containing tiny pores of a precise and uniform size that is used as an adsorbent for gases and liquids.

- N -

Nitrate

In the photographic context, a transparent plastic base that was used for photographic film until 1949 in the USA. Obtained from the treatment of cellulose with nitric acid.

Nitrate decay

Degradation of cellulose nitrate film base that may cause yellowing, buckling, film distortion, and corrosion of metal cans. Can also cause gelatin binder to become soft or sticky or to disintegrate.

- O -

Organic materials

Derived from once-living things, i.e., plants or animals. These materials contain carbon, are combustible, and are susceptible to deterioration from extremes and changes in relative humidity and temperature. They absorb moisture from their surroundings (i.e., are hygroscopic) and release moisture to the surrounding air in order to reach equilibrium. They are sensitive to light and are a source of food for mold, insects, and vermin.

Outgassing

The tendency of some materials, e.g., acetate and nitrate film bases, to give off vapors as they decay. Some of these vapors may be harmful.

Oxidation

The chemical action of electron removal from one atom or molecule by another atom or molecule often resulting in image fade or paper weakening.

- P -

PAT (Photographic activity test)

A test method described in ISO 18916 that is used to predict certain chemical interactions between enclosure materials and photographic images.

PI (Preservation index)

A means of expressing how ambient temperature and RH affect the chemical decay rate of collections. PI illustrates, in years, how long it will take for vulnerable organic materials such as poor-quality paper to become noticeably deteriorated under current (and unchanging) environmental conditions. PI is not a predictor of the useful life of any object or collection but is a convenient comparative measure, using short-lived materials as a yardstick.

Polarizer

A sheet, containing oriented particles, that transmits light that vibrates in only one direction.

Polyester

A transparent plastic base for photographic film and magnetic tape that is composed of a polymer of ethylene glycol and terephthalic (or naphthalene dicarboxylic) acid. It is very strong and stable.

- R -

RC

An acronym for “resin-coated.” A polyethylene film applied to both sides of photographic paper base for the purpose of speeding processing and drying.

RH (Relative humidity)

The amount of water vapor in the air expressed as a percentage of the maximum amount that the air could hold at the given temperature.

- S -

Sheet film

A single piece of flat (non-roll) film found in various formats, such as 4” x 5” or 5” x 7”.

Silver image decay

A defect of a black-and-white silver image, which can be manifested as microspots, silver mirroring, or overall image discoloration.

Silver mirroring

Oxidation of black-and-white images, in which the image silver migrates to the surface, creating a mirror-like appearance.

Support

The glass, plastic, or paper base on which the image layers of photographic film, prints, or magnetic tape are coated.

System obsolescence

A problem associated with machine-readable images, data, or sound recordings, whereby the information can be recovered only by using hardware or software that is obsolete.

- T -

Tape deformation

Distortion of magnetic tape resulting in lack of flatness. (See also Buckling.)

Thermal equilibration

The process by which the temperature of an object becomes the same as that of its environment, or the state of having the same temperature as that of the environment.

TWPI (Time-weighted preservation index)

Adds the element of time and the cumulative effect of deterioration to the PI to give a more realistic estimate of the long-term effect of an environment on preservation. TWPI illustrates the effects of fluctuating conditions, over a whole period of time, as a single value. It is the harmonic mean of the PIs: a more correct way of averaging PI than the arithmetic mean ordinarily used.

- V -

Vinegar syndrome

This slow form of chemical deterioration of cellulose acetate film is caused by poor storage conditions. It is so named because, as film degrades, it gradually shrinks, becomes brittle, and generates acetic acid, which evaporates into the air, producing a sharp, vinegar odor.

- Y -

Yellowing

Discoloration that affects a color image or, in earlier color processes, the white border of a print.