OIL & COLOUR CHEMISTS' ASSOCIATION
SOUTHERN AFRICA

Encyclopedia of Terms and Definitions used in the Surface Coating Industry
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- A -BACK TO INDEX

Anti-Foaming agent:-

An additive used to minimise the formation of foam during processing. A problem most often found in the manufacture of water-based coating systems but not exclusively. see Defoamer

Abrasion:-

Wearing away of a surface by action such as rubbing, scraping or erosion

Accelerator:-

Any substance that increases the speed of a chemical reaction. In paint terms, it usually indicates a material that hastens the curing or cross-linking of a resin system

Acicular:-

Needle shaped particles Length at least 3 times the width

Acid value:-

The number of milligrams of KOH required to neutralise the free acids in 1 gram of vegetable oil, resin etc

Addition polymerisation:-

A chemical reaction in which small molecules (monomers) combine to form a polymer without splitting off water or other simple molecules.See Condensation Polymerisation,

Additive:-

Any substance added, in small quantities, to a coating material to improve or modify one or more properties.

Adhesion:-

The degree of attachment between a film of a coating material and the substrate with which it is in contact. One metod of evaluating this is the CROSS-CUT TEST.
The latter may refer to another film (intercoat adhesion) or to the substrate material. cf Cohesion. MORE

Agglomerate:-

A loose arrangement of primary particles and aggregates of a pigment, attached, for example, at their corners or edges, which may be broken down during dispersion in the paint making process

Aggregate:-

A group of dry pigment particles held together by surface forces - the spaces between the particles are filled with air.

Air drying:-

An ambiguous term. Can describe drying of a paint film at room temperature or drying by means of oxygen from the air

Aerosol:-

Composition (Paint, insecticide or similar) where the propellant is a liquid/solvent under pressure. Release causes atomisation and so is used as a spray.

Alkali:-

A molecular or ionic substance that can combine with a proton to produce a new compound (soaps, salts). A compound having highly basic properties, that readily ionises in aqueous solutions to yield OH anions, with a pH of above 7.

Alkyd resin:-

A synthetic resin made by condensation between a polyhydric alcohol such as glycerol and a polybasic acid such as phthalic acid (normally the anhydride). Modifying materials are often used, e.g. vegetable oil fatty acids. Alkyds are the most commonly used synthetic resins in the coatings industry.
There is often some confusion here. The original Alkyd was a polyester used as an insulation varnish and was later oil modified for the coatings industry. Generally in the coatings industry the term Alkyd is applied to the oil modified versions. The term "Oil Free Alkyd" is sometimes used in reference to a polyester.

Amino resin:-

A synthetic resin of the thermosetting type, made by the reaction of nitrogen containing compounds, such as urea and melamine, with formaldehyde. They are usually blended with other resins (e.g. alkyds or epoxies) and are usually cured by stoving.

Anti-foaming agent:-

A product used to diminish the tendency for the formation of air bubbles during the manufacture and application of coating systems.

Aqueous:-

Of, or like, water. In coatings terms, having water as the main solvent or diluent.

Apparent Density:-

The apparent volume occupied by a granular or other loosely packed substance. The voids or air spaces are included in the volume. Used for shipping and packaging. usually expressed in mass/cubic metre. see Packing Density, Bulking value. Tamped Volume.

- B -BACK TO INDEX

Batch:-

The final quantity of any type of coating material produced in a single series of manufacturing operations.

Batch Card:-

The record of the ingredients used in the manufacture of a given batch of a coating material, together with any subsequent additions to modify or standardise the batch.

Baking:-

The process of drying and hardening a coatings material by the application of heat, usually in some form of oven. See - Stoving.

Ball mill:-

Equipment used to disperse pigments; usually comprising a steel cylinder lined with ceramic blocks, and containing ceramic or porcelain balls or pebbles as grinding media. The cylinder rotates at a relatively slow speed, allowing the balls to cascade through the mill base, thus grinding or dispersing the pigment

Binder:-

The component of a coating material that binds the pigment particles (if present) together, and after drying and/or curing, produces a coherent and adherent film

Biocide:-

A chemical agent capable of killing organisms Bittiness. Dirt on surface. Caused by dirt in paint. Poor air cleaning. Dirt in gun. Dirty working conditions. Compressor not blown down.

Bitumen;-

term for natural and synthetic hydrocarbon resins such as asphalts, tars and pitches. They are dark in colour, non-convertible, viscous liquids or solids

Blistering:-

Swollen areas. Can be caused by oil or grease under film, water in spray line or trapped solvent during spraying or transmission of moisture through film. See Osmosis. Also materials coming from porous substrates Blistering occurs when co-hesion is greater than adhesion. The film remains intact but is detached from the substrate.
See Adhesion & Cohesion. MORE


Photo Courtesy KVB, Photo Courtesy SATA
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Blow-down:-

Releasing the air from the bottom of the reservoir of the air-compressor at prescribed intervals or at the end of day. This removes the excess of oil-contaminated water which accumulates during operation.

Blushing:-

White milky appearance or haziness in film caused by the condensation of water on the surface. Caused by thinners evaporating too fast in high humidity. May disappear on heating. Polar solvents can help in reducing or eliminating. See bloom - external, blushing, haze .

Bloom - internal:-

Generally caused by wrong balance in thinners of diluent/solvents. See Haze, blushing, bloom - external.

Bloom - external:-

White milky appearance on film. Caused by thinners evaporating too fast in high humidity. Water condenses on cold surface. May disappear on heating. Polar solvents can help in reducing or eliminating. See Blushing, bloom, haze

Bonding Liquid:-

A low viscosity resin solution used to bind together loose particles on a surface before overcoating. Often confused with sealers these preparations act as an adhesive for the loose particles and generally, to be really effective, should be of such a low viscosity as to be absorbed into powdery surfaces. See also sealer, size, filler, primer, undercoat.

Body:-

See consistency

Boiling point:-

Temperature at which the vapour pressure of a liquid is just above the total pressure of its surroundings. At this stage, the liquid is rapidly converted into the vapour state. MORE

Boot-topping Paint:-

A particular type of marine paint used to accord protection to that part of a ship's hull at the "wind and water" line.

Build coat:-

A coating applied for the purpose of giving film thickness to a coating. Particularly important when using relatively low solids coatings such as vinyls where a minimum dry film thickness is important. It may be a more heavily filled version of the finish coat or a variation on the primer or undercoat.see undercoat.

Bulking value:-

The apparent volume occupied by a granular or other loosely packed substance. The voids or air spaces are included in the volume. Used for shipping and packaging. usually expressed in mass/cubic metre. see Apparent Density, Bulking value. Tamped Volume.

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Caking:-

Settling of a dense deposit in a coating material that cannot be re-dispersed by simple stirring. Catalyst A substance that increases the rate of a chemical reaction, but remains chemically unchanged at the end of the reaction. The term is often wrongly used for materials that enter into the reaction e.g. hardeners or curing agents

Cellulose:-

A non-convertible resin produced by the nitration of nitrate cellulose. They are soluble in esters and ketones, with some grades soluble in alcohols. Nitrocellulose, or N/C, is a misnomer, as they contain nitrate groups, not nitro groups.

Chain stopper:-

A substance either added or formed during the polymerisation process which inhibits further increase in the length of the polymer chains.

Chalking (1):-

Formation of a friable powder on the surface of a coating giving a chalky appearance. Caused by disintegration of the binder by weathering (oxidation and or UV degradation) and release of the pigments and/or extenders at the surface. The "Chalk" can be removed from the surface by rubbing which reveals the original colour beneath. If left the chalk will generally reappear.
Epoxy coatings are particularly prone to the phenomenon. Not to be confused with FADING.


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Chalking (2):-

Formation of a powdery surface while spraying. This caused by too much fine overspray usually from too high a pressure at atomisation and thinners evaporating too fast between the gun nozzle and the job. The fine aerosol formed looses its solvent and is deposited in an almost dry form on the surface. Poor air extraction exacerbates the problem. The preferred term is "DRY SPRAY".

Checking:-

Crow's-foot or very fine wrinkling effect on surface or a fine wrinkle. Caused by extreme temperature changes or foul atmosphere. Thinner affecting previous coat. Coats too thick. In stoving can be caused by foul oven.

Chlorinated:-

Natural or synthetic rubber that has been chlorinated to increase its solubility in organic solvents. It possesses a high degree of chemical and water resistance.

Cissing:-

Small holes in the surface. Caused by oil grease or silicone contamination. See, fish eyes. Cratering

CLICK ON THE PICTURE TO ENLARGE
"Photo courtesy of Sata Sprayguns

Cloudiness:-

Lack of clarity or transparency in e.g. a binder solution, a solvent or a dried varnish film. (See opalescence)

Coalescence:-

The formation of a film of polymeric material when water evaporates from a dispersion or latex binder, permitting close contact between, and fusion of, adjacent binder particles.

Coalescing solvent:-

A solvent which, when added in limited quantities to certain water-based coatings, facilitates the formation of a continuous film of the binder.

Coating (noun):-

A film forming material applied to a substrate to provide a decorative, protective or functional adherent film

Condensation polymerisation:-

A chemical reaction in which small molecules (monomers) combine to form a polymer with the splitting off of water or other simple molecules, See Addition Polymerisation,

Cohesion:-

Propensity of a single substance to adhere to itself; internal attraction of molecular particles towards each other. The forces that bind a coating film into a coherent whole. cf Adhesion. MORE

Colourant:-

Any substance that imparts colour to another substance tic can be dyes or pigments; a concentrated pigment dispersion used to tint paints to a desired colour

Compatibility:-

Ability of two or more substances to form a stable homogeneous mixture when mixed with each other.

Consistency:-

A general term for the property of a material whereby it resists permanent change of shape

Contrast ratio:-

Ratio of the reflectance of a dry paint film, applied at a specified thickness over a black substrate, to the reflectance of a dry film of the same paint applied at the same film thickness over a white substrate.

Convertible:-

A coating whose binder undergoes a chemical change coating during drying. The change is not reversible, and the binder is no longer soluble in its original solvent.

Cosmetic corrosion:-

The type of corrosion that occurs on an automotive body when the steel substrate has been exposed as a result of adventitious mechanical damage.

Cratering:-

Small holes in the surface. Caused by oil grease or silicone contamination. See cissing, fish eyes.

CLICK ON THE PICTURE TO ENLARGE
"Photo courtesy of Sata Sprayguns

Critical Pigment Volume Concentration - CPVC.:-

The relationship of the volume of pigment to the total volume of the solid component of the paint. Many physical properties are influenced by PVC. and these include gloss, permeability, & tensile strength. In the case of gloss, permeability, & tensile strength a fairly well defined change which occurs at PVC of around 0 54. This is known as the "Critical Pigment Volume Concentration" (CPVC) and occurs close to this value for most pigment binder systems. (See Pigment Volume Concentration. Oil Absorbtion Gloss Assessment.)

Cross-cut adhesion test:-

A simple test to evaluate the adhesion of a coating to a substrate. MORE.


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- D -BACK TO INDEX

Defoamer:-

An substance used to remove foam produced in a paint during manufacture usually by processing errors. These can be added to the mix or may be sprayed onto the surface, See Anti-Foaming agent

Density:-

Mass per unit volume; expressed as gm/cm3, Kg/dm3 at a stated temperature. As the term density is used in reference to other things - fog, forests, population &c the term Relative Density is preferred but specific gravity is also widely used. See Relative density, specific gravity.

Dilatancy:-

Property of a fluid whose apparent viscosity increases with increased shear rate.

Diluent (a):-

A volatile liquid which, while not a solvent for a particular binder, may be added to the true solvent without causing precipitation. Also the liquid phase of a binder dispersion.

Diluent (b):-

A component of a system used to extend a composition. It should be compatible and relatively inert. It can give make a composition more cost effective even though there is some loss of properties. (An example is the use of hydrocarbon resin in epoxy systems.) See extender (2)

Dirt Pick-Up::-

The tendency of a film of a coating material to attract soiling material that cannot be removed by simple washing.

Dirt Retention:-

A defect characterised by the tendency of the dry film of a coating material to retain soiling material.

Dirt Resistance:-

The property of a film of a coating material to resist soiling, other than that from micro-organisms, which is deposited or embedded in the dried film.

Dispersion (n):-

A 2 phase system in which the one phase, called the disperse phase, is permanently distributed as small particles throughout the other phase, called the continuous phase. In coatings, we commonly deal with pigment dispersions and with binder dispersions. Can refer to the dispersion of a resin in a volatile organic liquid which is not a solvent for the resin.

Dispersion (v):-

The process of dispersing the pigment agglomerates supplied by the pigment manufacturer into primary particles and the wetting of these particles by media. How well this is achieved is then called the degree of dispersion. The term "grinding" is often used in the industry describe dispersion.

Drier:-

A material which accelerates the drying of vegetable oil based binders

Distinctness Of Image (DOI):-

The assessment of the gloss level of a coating system, particularly in the automotive field, which involves the comparison of the sharpness of an image as reflected by the system under test with that of an agreed standard. See Gloss Assessment.

Dry Film Thickness (DFT):-

Paints generally have two major components, one volatile and the other non-volatile. The non-volatile component is the functional surface coating. Thinners are used for viscosity adjustment for correct application. During and after application the thinner evaporates and thereafter takes no further part in the process. The durability and functionality depends upon attaining the optimum thickness of this film which, when measured, is termed the "Dry Film Thickness". Control of wet film thickness (WFT) during application is essential to ensure the correct dry film. Control of the wet film thickness during application ensures optimum & cost effective results. It must be remembered that the wet film thickness is changing immediately upon application due to solvent loss from the film and so must be read immediately. In some cases applicators also use the spreading rate to ensure correct thickness. See WFT.

Dry spray:-

Formation of a powdery surface while spraying. This caused by too much fine overspray usually from too high a pressure at atomisation and thinners evaporating too fast between the gun nozzle and the job. The fine aerosol formed looses its solvent and is deposited in an almost dry form on the surface. Poor air extraction exacerbates the problem.

Dye:-

A colourant that is generally organic in nature and soluble in the relevant solvent or media; it will absorb certain wavelengths of visible light and transmit the balance, but does not scatter light; is transparent

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Electrocoating:-

Method of paint application whereby an electric field deposition is used to promote the deposition of a coating material onto a substrate. The substrate acts as an electrode which attracts oppositely charged particles of paint in the dip tank.

Electrodeposition:-

See electrocoating

Emulsion:-

A two-phase system in which droplets of one liquid are dispersed in another liquid; the two are immiscible. The term is used incorrectly when applied to "emulsion paints ", as the system comprises solid particles (binder + pigment) dispersed in a liquid. See Latex. "Emulsion" paints are so called because the binder is made by an emulsion polymerisation process in which the liquid phase is converted to a solid - actually a latex.

Ester Condensation:-

A chemical reaction in which an ester or polyester is formed with the splitting off of water. See Condensation Polymerisation & Addition Polymerisation,

Ester Gum:-

A resin made by reacting rosin or rosin acids and a polyol.

Evaporation rate:-

The time required for a given amount of a material to evaporate compared with the time required to evaporate the same amount of a known material (usually n butyl acetate or ethyl ether Standard must be quoted).MORE

Extender (1):-

A solid material used as an additive to impart other specific physical properties to a coating; they are often natural minerals such as talc, kaolin, whiting etc. The preferred term is generally "extender". The term is derived from the term "pigment extender" as they are generally pigment-like in nature but possess poor optical properties. Pigments themselves are generally too expensive to use to modify properties other than colour. An example of a case where both pigmentation and other properties are filled by the same substance would be a red oxide primer. See also See also sealer, size, filler, bonding liquid, undercoat..

Extender (2):-

The term extender is sometimes applied to resinous materials added to such systems as epoxy solutions. They are used to reduce costs and can modify flow and other characteristics they may be referred to as "diluents".

- F -BACK TO INDEX

Face Colour:-

Term used to describe the colour observed on paints, (particularly metallic paints) when they are viewed near to the normal. It may also be referred to as the "Top Colour". It is generally used in contrast to the term "Flop Colour", which is the colour observed near to the grazing angle, ie. nearly parallel to the surface (See FLOP COLOUR).

Fading:-

The loss of colour caused by a change in the colourant used in the film (pigment or dye). Generally the colour becomes lighter but any more resistant colourants will dominate. Differs from chalking q.v.

Filler:-

1) A solid substance used to impart other specific physical properties to a coating. The term refers to the function as they are the same substances used as extenders. These materials generally only add bulk and physical properties and colour is often of little significance. See also extender.
2).Preparations used as putties, gap fillers and surfacers

Fineness of grind:-

An assessment of the degree of dispersion as judged by the presence of coarse particles; a grind gauge is used for the purpose, See F.O.G. MORE

Fire Retardant Paint:-

A type of coating material which when exposed to heat is capable of impeding the spread of combustion (see Intumescent Coatings).

Fish eyes:-

Small holes in the surface. Caused by oil grease or silicone contamination. See cissing,. Cratering

Flash point:-

The lowest temperature of a liquid at which it gives off sufficient vapour to form an igniteable mixture with the air at the surface of the liquid. MORE

Flash Rusting:-

The rapid and irreversible formation of rust stains in a water-borne coating material, especially when applied to blast-cleaned ferrous substrates, and which persist throughout the life of the film.

Flocculation:-

Pigment particles suspended in a mill base in the absence of dispersion forces, for example if the mill stops, may combine together to form clusters or flocculates. These flocculates consisting of pigment particles and some liquid are thixotropic and may be broken down by renewed application of dispersion forces. In severe cases (pigment shock) flocculation may be irreversible.

Flop:-

Where two different painted panels appear to be a good match for colour when viewed at a given angle, but which appear different in colour at all other angles. Also known as Geometric Metamerism.

Flop Colour:-

Term used to describe the colour observed on paints (particularly metallic paints) when they are viewed near to the grazing angle, i.e. nearly parallel to the surface. The term is generally used in antithesis to the terms "Face Colour" or "Top Colour" - the colour observed when the surface is veiwed at an angle near to the normal. (See FACE COLOUR).

F.O.G.:-

An assessment of the degree of dispersion as judged by the presence of coarse particles; a grind gauge is used for the purpose, See Fineness of grind. MORE

Ford Cup:-

An effluent type viscometer of particular use in the measurement of non-thixotropic paints. The size of the aperture must be specified (ie No. 4). The time taken for the paint to drain from the cup is expressed in seconds at a set temperature. MORE
See also Viscosity, Krebs Stormer, Gardner Tubes
A viscosity calculator is available at the VISCO website. CLICK HERE

Frosting:-

An extremely fine wrinkle on the surface of a coating generally caused by foul gases in the curing oven. Direct fired ovens are generally prone to give this effect. See Gas Checking.

- G -BACK TO INDEX

Gardner-holt Tubes

A set of calibrated tubes containg the same quantity of liquid each with a different viscosity. When inverted of a bubble will rise up the tube. The speed at which the bubble ascends in a control tube is compared to that of a standard. The tubes are lettered A - Z. Useful for clear solutrions of resins. MORE.
See also Ford Cup, Krebs Stormer, Viscosity


A viscosity calculator is available at the VISCO website. CLICK HERE

Gassing:-

The formation, in the can, of gaseous products in a coating material, due to the reaction between two or more constituents of the coating material or between the latter and the metal of the container (see Putrefaction). Occurs in paints containing aluminium metallic pigments if moisture is present or acidity is too high. Special additives - moisture absorbants assist in minimising the problem.

Gas Checking:-

An extremely fine wrinkle on the surface of a coating generally caused by foul gases in the curing oven. Direct fired ovens are generally prone to give this effect. See Frosting.

Gloss Assessment

The gloss of a coating can be assessed by physical observation however the source of the light and the angle of observation causes differences. For reproducible results these must be controlled. Glossmeters measure the surface using 3 angles of incidence - 20, 60 and 85 (from the vertical)MORE

Grinding

With natural pigments, and with synthetic pigments after high temperature sintering, this involves actual reduction in particle size a process carried out by the pigment manufacturer.

Grip Coat:-

A film of a coating material which, when applied to a substrate, bare or already painted, enhances the adhesion of a subsequent film of another coating material. - See Key Coat.

- H -BACK TO INDEX

Hard dry:-

When a thumb (or substitute thereof) , exerting a measurable downwards pressure, leaves no permanent mark or damage on the coating film. It is the stage when the. paint film can be handled without damage.

Hardener:-

A material, generally part of a two component paint system, which reacts with the other binder component to produce a fully cured coating. Often wrongly called a "catalyst " (qv)

Hardness:-

The ability of a coating film, as distinct from the substrate, to resist cutting, indentation or penetration. MORE

Haze:-

Haziness in film caused by the throw-out of components. Generally caused by wrong balance in thinners of diluent/solvents. See Bloom - internal.

Hiding power:-

A measure of opacity. It is the spreading rate at which a paint just obliterates a specified black and white surface when a film is applied according to a standard method; it is expressed in square meters per litre

Holding Primer:-

A low-build blast primer used to provide a temporary protection to steelwork until the complete paint system can be applied in accordance with accepted practice.

Humectant:-

A material capable of retaining moisture.

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Intermediate Coat:-

Any film of coating material that lies between the primary and finishing coats of a coating system.

Intumescent Coating:-

A coating material which by foaming or swelling forms a voluminous substance when exposed to heat

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- K -BACK TO INDEX

Key Coat:-

A film of a coating material which, when applied to a substrate, bare or already painted, enhances the adhesion of a subsequent film of another coating material. - See Grip Coat.

Knotting:-

Solution of shellac in alcohol solvent used to seal the knots found in new wood.

Krebs Stormer:-

Rotational viscometer which is relatively simple to use and reads viscosities for thixotropic liquids in the "brushing" range. The apparatus basically measures the force required to rotate a paddle at a speed of 200 rpm in the test liquid. The viscosity is expressed in Krebs units MORE.
See also Viscosity, Ford Cup Gardner Tubes
A viscosity calculator is available at the VISCO website. CLICK HERE

- L -BACK TO INDEX

Lacquer:-

A coating based on a non convertible binder which dries purely by solvent evaporation

Lacquer dry:-

The initial drying phase of a system (often a blend of convertible and non-convertible binders). The system dries to tack free like a lacquer but needs time to fully convert. Examples - styrenated alkyd, n/c alkyd blends.

Latex:-

A dispersion of a solid in a liquid. Often used as a synonym for a dispersion binder. a dispersion of a polymer in an essentially aqueous medium. See emulsion.

Lead Compounds:-

Lead compounds have been used in paints since early days. Due to the toxicity of lead in various forms there use has been greatly reduced. MORE

Lead Pigments:-

Lead pigments have been used in paints since early days. Red Lead, lead tetroxide Pb3O4, was used as a primer for steel. White Lead, lead carbonate PbCO3 or lead sulphate PbSO4.PbO as a primer for wood and in earlier times as a white pigment. Other coloured pigments were based upon the chromates and these are still used mainly in industrial coatings. Lead pigments are no longer used to any extent in decorative paints due to the toxicity. MORE

Let down:-

The process when the millbase is gradually diluted with the balance of the ingredients in the formula.

Lifting:-

Rising of dry film on application of second coat or on submersion in a liquid. Effect caused by paint removers. Film detaches and crumples. Coating with non-recommended top coat. Incorrect thinners attacking convertible coating. See wrinkling.

- M -BACK TO INDEX

Mar Resistance:-

The ability of a coating to resist damage caused by light abrasion, impact or pressure.

Medium:-

The phase in which the pigment is dispersed; the vehicle; often a solution of binder, solvent and dispersion additives.

Methylated Spirit:-

A commercial version of Ethyl Alcohol which has been made non-potable by the addition of adultarants. The original adultarant was methyl alcohol along with substances to give it a bitter taste and a repellent odour. For retail sale it can be coloured blue with a dye. Methyl Alcohol, because of its potency is no longer the preferred common adultarant and other solvents such as aliphatics are used. Often supplied as 64OP (64 degrees over proof) or 74OP (74 degrees over proof) indicating the presence of water.- see PROOF SPIRIT

Mill base:-

That portion of the coating formulation that is charged into the dispersion mill; a high concentration of pigment mixed with medium suitable for the dispersion process.

Millscale:-

A blue-black shiny deposit of Iron Oxide (magnetite) which is caused by the heating and hammering or rolling of the metal. It is very brittle and rust can form underneath it and so cause detachment of the scale and the paint. It must be removed if a durable finish is required. Millscale is found on any steel substrate which has been heated & worked, e.g. rolled, hammered or welded. It is in fact very misleading as it provides a temporary protective coating but, once exposed to the weather, rust creep which will start at the edges. The millscale and the coating will then become detached. Tubes and sections, angle iron, as well as plate, used for tanks and ships, fall into this category. It is very important to recognise millscale as it must be removed for a successful lasting paint finish. Exposing the metal to the atmosphere will cause the millscale to detach. The exposed steel will then rust on the surface. This is easily removed. Other methods of removal include chipping, acid picking and grit blasting.

Mineral turpentine:-

See white spirits

Mineral spirits:-

see white spirits

Mohs scale:-

The relative hardness of minerals is determined according to the Mohs scale of hardness. MORE

Mottling:-

Uneven effect in metallic finishes. Caused by heavy wet coats. Build-up of electrostatic charges. Poor mixing of paint. Conditions too cold.

- N -BACK TO INDEX

Newtonian:-

Liquid in which the rate of shear is proportional to the shear stress. In practical terms, the viscosity does not change with changes in shear rate, nor is it time dependent.

Non aqueous:-

A dispersion of a binder in an organic liquid which is a dispersant not a solvent for the binder. e.g. an organosol.

Non convertible:-

A binder which yields a film which, after drying, can binder be redissolved in its original solvent

Non Newtonian:-

A fluid in which the rate of shear is not proportional to the shear stress. Liquids where the viscosity is affected by concentration and temperature only.

Non volatile:-

The solid material remaining after the volatile has content been driven off or evaporated.

No Pick-Up Time:-

The period between the application of a film of a road-marking paint and the precise moment when the film is no longer removed by an apparatus that simulates the passage of a tyre over the surface of the film.

- O -BACK TO INDEX

Oil absorption:-

The amount in grams of linseed oil of a specified acid value. expressed as grams of oil required to wet out 100 grams of the pigment under test. The test conditions and end point are carefully defined. (See Critical Pigment Volume Concentration - CPVC, Pigment Volume Concentration - PVC)

Opacity:-

The degree to which a material obscures or hides a substrate.

Organosol:-

A composition based upon a resin solution in a volatile organic liquid. Often used in reference to aerosol paints where the propellant is a liquid/solvent under pressure.

Orange Peel:-

Surface mottled like skin of an orange. Caused by poor flow. Coats too thick. Surface drying too quick. Poor atomisation.

Osmosis:-

The passage of water in molecular form through a paint film (a semi-permeable membrane). Moisture will pass through a semi-permeable membrane if there is a soluble substance present - even in minute quantities. If the film with the solution thus formed (in or under it) is exposed to water with less solute (more dilute) moisture will pass in the direction from the weaker to the stronger this creates a pressure (Osmotic pressure) and a bubble will form. See blisters.MORE

Overprint Varnish:-

A clear coating material designed for use over films applied by a printing process.

- P -BACK TO INDEX

Packing Density:-

The mass of a given volume of substance as supplied. This includes all voids. See Tamped volume, Bulking value. Apparent Density.

Particle size:-

The relative percentage (usually by weight) of each of distribution the different size fractions of a powdered material MORE

Paste Dispersion:-

Occurs when two liquids usually one being of higher viscosity, are mixed. One paste can then be broken down slowly into smaller globules and stay suspended in the other. This can occur during tinting if there is insufficient agitation. A thick liquid should always have a less viscous one added to it slowly under good agitation.

Pigment:-

A powdered insoluble solid which provides optical properties such as colour, reflectance, opacity. The term is also used in the coatings/ink industry for powders which, when dispersed in a liquid or solid binder, may also provide properties such as UV protection, corrosion inhibition or for modifying mechanical and flow properties.

Pigment Volume Concentration PVC:-

The relationship of the volume of pigment to the total volume of the solid component of the paint. Many physical properties are influenced by PVC. and these include gloss, permeability, tensile strength. (See Critical Pigment Volume Concentration - CPVC, Oil Absorbtion.- Gloss Assessment)

Pin Holing:-

Small holes in film. Caused by moisture in airlines. Solvent trapped under film. See Solvent Popping, Cratering, cissing

Plastisol:-

A dispersion of fine polymer particles (usually PVC with plasticiser) in a non-volatile organic diluent. The polymer does not dissolve at ambient temperatures but upon heating the polymer dissolves and forms a solution which results in thermoplastic film/moulding upon cooling.

Polar:-

A molecule that has, or is capable of developing, electrical charges. Polar molecules ionise in aqueous solution and provide conductivity to a paint.

Polymer:-

Materials whose molecular structure consists of one or more structural units (monomers) repeated any number of times; a homopolymer has only one kind of structural unit which is repeated, while a copolymer has two or more different structural units which are repeated.

Polymerisation:-

A chemical reaction in which two or more small molecules (monomers) combine to form larger molecules (polymers) that contain repeating structural units of the original molecules.

Pretreatment:-

The chemical modification of substrates in order to improve adhesion, provide an even surface for painting and in the case of metals, to provide some protection against corrosion. e.g. phosphating of steel

Primary Particle:-

The smallest pigment particle size achieved by the pigment manufacturer. It is the ideal stage to be achieved in pigment dispersion. Note: The pigment manufacturer, or in the case of natural pigments the refiner, produces primary particles which are converted to agglomerates in the final processing stages.

Primer:-

The first coat in a paint system, whose main function is to provide the adhesion between substrate and the total paint system. See also sealer, size, filler, bonding liquid, undercoat.

Proof Spirit - Determination of the Strength of Ethyl Alcohol.

A mixture of 50% alcohol and 50% water burns readily, but one containing 48% alcohol and 52%e water burns with difficulty.. The latter mixture was called proof spirit, because originally an alcohol mixture was tested (or proved) by pouring it over gunpowder and igniting. If the gunpowder ignited, the spirit was over proof. Water was then added, and the number of volumes of water required to bring 100 volumes of the spirit under proof gave a rough measure of the strength. For example, 100 volumes of rectified spirits require 56 volumes of Water, hence the spirit is said to be 56 degrees over proof. This is not an accurate method, because a contraction in volume occurs when alcohol and water are mixed. The modern legally defined proof spirit contains 49,3 per cent. by weight of alcohol, which is just over 57 per cent. by volume. The modern method of estimation depends on a knowledge of the specific gravity of various alcohol-water mixtures. 200-300 c.cm. of the alcohol-containing liquid is distilled until the distillate measures about half the original volume. The distillate is then made up to the original volume of the alcoholic liquid with distilled water and the specific gravity determined with an accurate hydrometer. The temperature is noted and the percentage of alcohol obtained by reference to a set of tables. If the liquid is known to contain only water and alcohol the density measurements can be carried out directly. see Methylated Spirit

Pseudoplastic:-

A fluid whose viscosity decreases with an increase in fluid shear rate. The effect is not time dependent and the consistency curve shows no yield value

Primer Sealer:-

A coating material used to seal and simultaneously prime a suitably prepared substrate.

Putrefaction:-

The decomposition in the can resulting from bacterial attack on a coating material.

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Reactive Diluent:-

A liquid which reduces the viscosity of a preparation but which takes part in the film-forming process by combining with one or more of the constituents of a coating material.

Recoatability:-

The aptitude of a fully-dried film of a coating material to accept, without adverse effect, a subsequent coat of the same or similar material.

Relative density:-

The ratio of the density of a material to the density of water at the same temperature. This is the preferred term in place of "specific gravity" or "SG"

Rheology:-

The science of the deformation and flow of matter.

Roller Application:-

A process whereby the coating material is applied by means of a hand-held roller of some soft material (e.g. foamed plastic, fabric or wool).

Runs:-

Running of wet paint into uneven rivulets. Cause - paint too thin. Solvents very slow. Very cold conditions. See Sags.

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Sags:-

Partial slippage of paint. Thick areas like wide runs. Cause - Heavy thick coats. Gun too close. Badly adjusted gun. See Runs

Scumble:-

A decorative technique in which a colourant, usually pigmented, is applied over a base colour coat to produce special effects. Used by decorators to produce wood grain effects. Materials used were known as "Scumbles". As these were often under-bound they needed to be sealed with a varnish or "scumble glaze" to fix them.

Sealer:-

1) A coating whose main function is to reduce gross porosity or 2) to seal in aggressive chemicals (eg. alkalinity) See also primer, size, filler, bonding liquid, undercoat.

Shear rate:-

The rate of change of shear strain with time; for a laminar flow liquid, it is the velocity gradient between laminar layers

Shear stress:-

The tangential shearing force acting on a material to produce flow

Sheen:-

A low gloss with poor distinctness of image; synonymous with gloss measured at an angle of 85 degrees. See also Gloss Assessment

Shellac:-

An orange coloured naturally occurring resin, alcohol soluble. The secretion of a female insect (Laccifer lacca) found in Asia.

Size:-

A coating applied to a surface to improve the adhesion of the subsequent coats. A thin varnish used as a first coat in metal decorating (i.e., when printing tinplate sheets prior to forming into cans). In the decorative trade used on surfaces before applying wallpaper. Also applied to coatings for textiles which stiffen them.See also primer, sealer, filler, bonding liquid, undercoat.

Skinning:-

The formation of an insoluble layer of hardened paint on the top of a coating material in the can. Usually associated with vegetable oil based coatings such as alkyds when sufficient oxygen is present in the air space above the paint to cause oxidative drying. The small amount of air left in the top of a container on filling is absorbed by the paint and so, in effect, the paint is vacuum packed. Some operators will invert the can after filling to ensure that the paint will form a seal should the lid not fit absolutely gas tight. See Lifting; Wrinkling.


CLICK ON THE PICTURE TO ENLARGE
"INK SKIN - Photo courtesy of Mike Miller - Canada"

Solids content:-

The non-volatile content; the solid matter remaining after the coating has dried; can be expressed by mass or by volume

Solvent:-

A liquid, usually volatile, which is used to dissolve the binder in a coating, and which reduces the viscosity of the coating, See diluent.

Solvent Popping:-

Small holes in film. Caused by moisture in airlines or solvent trapped under film. See Pin Holing, Cratering, cissing.


CLICK ON THE PICTURE TO ENLARGE
"Photo courtesy of Sata Sprayguns

Specular:-

Mirrorlike reflectance, The incident light beam is at reflection the same but opposite angle to the reflected light beam.

Spreading rate:-

The area covered by a litre of paint; expressed in square meters per litre; the practical spreading rate is the average area covered by a litre of paint when applied over a normal surface using appropriate means; paint applied at the recommended spreading rate should provide the desired properties (opacity, protection, etc)

Stainer:-

See colourant

Stoving:-

See baking

Strain:-

The changes in the dimensions of a body which accompany a stress

Stress:-

Resistance to deformation developed within a specimen subjected to an external force

Substrate:-

Any surface to which a coating is applied

Surface dry:-

The state of drying when slight pressure with a finger does not leave an imprint or reveal tackiness; when dry sand applied according to a standard method can be brushed off the coating without sticking to or causing damage to the surface,

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Tamped Volume:-

The apparent volume occupied by a granular or other loosely packed substance after tamping or vibrating. The voids or air spaces are included in the volume. Used for shipping and packaging. usually expressed in mass/cubic metre. see Packing Density, Bulking value. Apparent Density.

Thermoplastic:-

A material which is softened by heat and hardens on cooling. the process of softening and hardening can be repeated,

Thermoset:-

A material which permanently hardens (polymerises) when heated but is not softened by heat.

Thinner:-

A volatile organic liquid used to reduce the viscosity of a coating' often a blend of different solvents and diluents

Thixotropic fluid:-

A material that undergoes a reduction in apparent fluid viscosity when subjected to shear stress, followed by a gradual recovery in viscosity when the stress is removed. The effect is time dependent - at a constant shear rate the viscosity will reduce with time until it reaches a minimum value at a given temperature . There is a minimum value for shear stress (the yield value) below which no flow occurs.

Threshold limit:-

Refers to airborne concentrations of substances, and value (TLV threshold limit value) represents the highest concentration of the substance to which a person can be repeatedly exposed, without adverse effect

Time weighted average:-

The allowable time weighted average concentration over average TWA a normal 8 hour day or 40 hour week; see Threshold limit.

Tinter:-

See colourant or stainer

Tinting Strength:-

The degree to which a pigment imparts colour depth to another pigment; usually expressed as a percentage relative to a standard coloured pigment.

Topcoat:-

The last coating applied in a system; provides most of the decorative and protective properties

Touch dry:-

See surface dry

Triple roller:-

A type of mill used to disperse pigments; the pigments mill are dispersed by passing between accurately machined steel or granite rollers. The gap between the rollers can be precisely controlled, and the three rollers rotate at different relative speeds and often move laterally, thus providing a strong shearing force. Used for high viscosity dispersions (pastes and printing inks)

Turpentine:-

A colourless volatile oil distilled from the products of certain pine trees; now generally replaced by mineral spirit or white spirit due to cost and toxicity effects. Still used by some artists who wish to be traditional.

Turpentine substitute:-

Commercial name given to mineral/white spirit.

Undercoat:-

A highly pigmented coating applied after a primer to give a thick opaque low gloss film. It provides hiding power and film build. It can also serve the purpose of a filler coat which can be easily abraded to produce an even substrate for the topcoat. It can also provide better adhesion of a topcoat to the substrate. See also sealer, size, filler, bonding liquid, bonding liquid, build coat.

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Varnish:-

A transparent coating material based essentially on resins and/or drying oil and solvent.

Vehicle:-

The liquid portion of a coating, in which the pigment is dispersed; see medium

Vehicle Refinishing Paint:-

A coating material that has been formulated to reproduce, as closely as possible, the colour, gloss and durability of the coating material that was applied originally to an automotive body and which has been subsequently damaged or has deteriorated.

Viscosity:-

The internal resistance to flow possessed by a fluid; the rate of flow of a material when a force is applied to it . There are various methods of reading this depending upon the nature of the substance under examination. Viscosity is often refered to as the "thinness" or " thickness" of a liquid material but, as in the case of density, this should be avoided as too broad a definition. MORE.
See also Ford Cup, Krebs Stormer, Gardner Tubes
A viscosity calculator is available at the VISCO website. CLICK HERE

Volatile content:-

The percentage of the mass of a coating which is lost when the coating has dried completely

Volatile Organic Compound (VOC):-

Fundamentally any organic liquid or solid that vaporises spontaneously at the prevailing temperature and pressure of the surrounding atmosphere.

Volatile Organic Compound Content (VOCC):-

The mass of the volatile organic compounds present in a coating material, as determined under specified conditions.

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Wet Film Thickness (WFT):-

Paints generally have two major components, one volatile and the other non-volatile. The non-volatile component is the functional surface coating. Thinners are used for viscosity adjustment for correct application. During and after application the thinner evaporates and thereafter takes no further part in the process. The durability and functionality depends upon attaining the optimum thickness of this film which, when measured, is termed the "Dry Film Thickness". Control of wet film thickness (WFT) during application is essential to ensure the correct dry film. Control of the wet film thickness during application ensures optimum & cost effective results. It must be remembered that the wet film thickness is changing immediately upon application due to solvent loss from the film and so must be read immediately. The measurement of Wet Film Thickness can be non-destructive and relatively easy whereas the measurement of dry film thickness can depend upon the substrate but gauges are now available for a variety of substrates. Timber and masonry surfaces are particularly difficult. In some cases applicators also use the spreading rate to ensure correct thickness.
A SIMPLE WET FILM THICKNESS GUAGE

See DFT

White spirit:-

A petroleum distillate having a wide boiling range; a mixture of aliphatic and aromatic hydrocarbons used as a solvent. See Mineral spirit, Turpentine substitute.

Wrinkling:-

Wrinkles in film on drying. Causes - wrong driers, too thick a coat. Film detaches and crumples when second coat applied. Caused by non-recommended top coat. Incorrect thinners attacking convertible coating. Coating insufficiently cured. See. Lifting, Skinning, frosting.

Wrinkle Finish:-

Coating which upon drying gives a wrinlkled appearance. One favoured for office machines. Generally based upon a conjugated vegetable oil such as Tung or Dehydrated Castor and an excess of cobalt drier.

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Yield value:-

The minimum shear stress which must be applied to a liquid to start laminar flow. see thixotropic fluid


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