Powder Coating Glossary: 108 Terms Defined
A working glossary of powder coating terminology: 108 terms defined in plain English, with the test methods and standards that sit behind them. Written for engineers, buyers, fabricators and applicators who need to read a specification or a data sheet and know exactly what it is claiming.
Terms are listed alphabetically. Each links to the concepts it depends on where that helps.
Jump to a letter
A · B · C · D · E · F · G · H · I · M · N · O · P · Q · R · S · T · U · V · W · Z
A
Adhesion
Testing
The bond between the cured coating film and the substrate. Measured by cross-hatch test to ASTM D3359 / ISO 2409, rated 5B / GT-0 (best) to 0B / GT-5 (worst). Almost always determined by pre-treatment quality rather than by the powder.
Anodising
Comparison
An electrochemical process that thickens the natural oxide layer on aluminium. An alternative to powder coating for aluminium, with a narrower colour range but no organic film to chalk.
ASTM B117
Testing
The neutral salt spray test method. Panels are exposed to a 5 % salt fog at 35 °C and assessed for rust creep from a scribe. Reported in hours. Comparative only, it does not convert to years of service life.
ASTM D2247
Testing
Humidity resistance test, continuous condensing humidity at 100 % RH. Reported in hours to first blistering.
ASTM D2794
Testing
Impact resistance by falling weight. A hemispherical indenter is dropped onto a coated panel; the film must not crack or detach.
ASTM D3359
Testing
Cross-hatch adhesion. A lattice is cut through the film, tape is applied and removed, and the amount of coating detached is rated.
ASTM D3363
Testing
Pencil hardness. Pencils of graded hardness are pushed across the film; the hardest that does not gouge it is the rating. Typical thermoset powders rate H to 2H.
ASTM D523
Testing
Specular gloss measurement, usually at 60°, reported in gloss units (GU). The international equivalent is ISO 2813.
ASTM G154
Testing
QUV accelerated weathering using fluorescent UV lamps with condensation cycles. Reported in hours. Used to compare exterior durability between coatings.
B
Back-ionisation
Defects
Excess charge building in the deposited powder layer until it discharges back through the film, creating a pitted, starry texture and repelling further powder. Caused by too much gun voltage.
Batch
Commercial
One production lot of powder. Colour can vary slightly between batches, so a single visible assembly should be coated from one batch.
Blistering
Defects
Raised bubbles in the film, caused by trapped moisture, outgassing or corrosion progressing beneath the coating.
Bonded metallic
Finishes
A metallic powder in which aluminium or mica flake has been fused to the resin particle, so flake and resin cannot separate during application or reclaim. More consistent than a dry blend.
Booth
Equipment
The enclosure in which powder is sprayed, incorporating extraction and reclaim.
C
Chalking
Defects
Surface degradation under UV in which resin at the film surface breaks down, leaving loose pigment. The finish dulls and a wiped finger comes away powdery. Characteristic of epoxy and epoxy-hybrid coatings used outdoors.
Chemical resistance
Performance
The film's ability to withstand acids, alkalis and solvents without softening, blistering or losing adhesion. Tested to ASTM D1308. Pure epoxy chemistries perform best.
Chrome-free pre-treatment
Pre-treatment
Conversion coatings based on zirconium, titanium or silane rather than hexavalent chromium. Increasingly specified for environmental and regulatory reasons.
Cissing
Defects
Another term for cratering or fisheyeing, the film retracting from a contaminated spot.
Conversion coating
Pre-treatment
A chemical layer formed on the metal, phosphate, chromate or chrome-free, that improves adhesion and corrosion resistance before coating. Not optional for any serious application.
Corona charging
Equipment
The most common electrostatic method. A high-voltage electrode at the gun tip ionises air, charging powder particles as they pass. Simple and fast, but prone to the Faraday cage effect.
Coverage
Commercial
The area a given weight of powder will coat, dependent on film thickness, part geometry and transfer efficiency. Comparing quotes on cost per square metre rather than cost per kilogram is the only meaningful comparison.
Cratering
Defects
Circular depressions caused by low-surface-tension contamination, usually silicone or oil. Also called fisheyes.
Crosslinking
Chemistry
The chemical reaction during cure in which resin and curing agent form a three-dimensional network. This is what makes a thermoset irreversible, it cannot be remelted.
Cure
Process
The heating stage in which powder melts, flows and crosslinks into a continuous film. Defined by metal temperature and dwell time, not by oven set-point.
Cure window
Process
The range of temperature and time over which a powder cures correctly. Below it the film is under-cured; above it, over-cured and brittle.
Curing agent
Chemistry
The component that reacts with the resin to crosslink it. Also called a hardener or crosslinker. TGIC and HAA are common polyester curing agents.
Curing oven
Equipment
The oven in which coated parts are cured. Convection is the most common type; infrared and hybrid ovens reduce ramp-up time.
Cyclone
Equipment
A reclaim device that separates usable powder from air by centrifugal force.
D
Degassing
Process
Preheating a porous or galvanised part above its cure temperature to drive off trapped gas before coating, preventing pinholes.
Delta E (ΔE)
Colour
A single number expressing the total colour difference between two samples in CIELab space. ΔE ≤ 1.5 is a tight commercial match; ΔE of 1 is roughly the threshold of visible difference for a trained observer.
DFT: dry film thickness
Measurement
The thickness of the cured film, measured in microns (µm) to ASTM D7091 / ISO 2808. The most under-specified and most consequential number in a coating specification.
Dry blend
Finishes
A metallic powder in which flake is simply mixed with resin particles rather than bonded. Cheaper than bonded metallic but prone to separation during reclaim and colour drift.
Duplex system
Performance
Hot-dip galvanising followed by powder coating. The two protect synergistically and typically outlast the sum of their individual lives.
E
E-coat
Comparison
Electrodeposition, a wet process depositing coating from an aqueous bath by electric current. Excellent throw into recesses; commonly used as a primer under powder in automotive.
Edge coverage
Performance
Film thickness at sharp edges, always the thinnest point on a part because surface tension pulls the melt away during flow-out. Breaking sharp edges to a radius helps more than any coating change.
Electrostatic spray
Process
The standard application method: powder is given an electric charge and sprayed at a grounded part, to which it clings until cured.
Erichsen cupping
Testing
A slow deformation test to ISO 1520 in which a ball is pressed into the reverse of a coated panel. Measures how far the film can deform before cracking, in millimetres.
Extrusion
Manufacturing
The stage in powder manufacture where premixed raw materials are melt-mixed in a twin-screw extruder to disperse pigment uniformly through the resin.
F
Faraday cage effect
Defects
The inability of an electrostatic field to reach into recesses and internal corners, leaving them thin or bare while flat faces coat perfectly. Mitigated by lower voltage, greater distance, or tribo guns.
Film build
Process
The thickness of powder deposited before cure. Distinct from dry film thickness, which is measured after.
Fisheye
Defects
See Cratering. A small circular void where the film pulled away from a contaminant.
Flow-out
Process
The stage during cure when melted powder levels into a smooth continuous film. Insufficient flow-out produces orange peel.
Fluidisation
Equipment
Aerating powder in a hopper so it behaves like a liquid and can be pumped consistently. Damp or sintered powder fluidises poorly.
G
Galvanising
Comparison
Zinc coating applied by hot dipping. Often combined with powder coating as a duplex system for long-life corrosion protection.
Gloss
Finishes
Specular reflectance measured at 60° and reported in gloss units. Roughly: above 80 GU high gloss, 55–70 satin, 8–11 matt, below 8 dead matt.
Gloss retention
Performance
The percentage of original gloss remaining after weathering. A key exterior durability measure, reported alongside QUV or Florida exposure hours.
Grounding
Process
Electrical earthing of the part so charged powder is attracted and held. Poor grounding is a frequent and easily missed cause of inconsistent deposition.
H
HAA
Chemistry
Hydroxyalkylamide, a TGIC-free curing agent for polyester powders. Widely used where TGIC is restricted, notably for European markets.
Hopper
Equipment
The fluidised container from which powder is fed to the gun.
Hybrid
Chemistry
An epoxy-polyester blend. Combines epoxy's mechanical and corrosion performance with polyester's decorative flexibility. Chalks under UV, so indoor use only.
I
Impact resistance
Performance
Ability to withstand a sudden blow without cracking or detaching, tested to ASTM D2794 / ISO 6272 in direct and reverse modes.
Iron phosphate
Pre-treatment
A lighter, cheaper conversion coating than zinc phosphate. Adequate for indoor service; not for demanding corrosion applications.
IS 101
Standards
The Indian Standard series of test methods for paints and related materials, referenced throughout IS 13871.
IS 13871
Standards
The Indian Standard for thermosetting powder coatings on mild steel, published 1993 and revised 2021. Classifies coatings as Grade A (gloss above 80), B (10–80) and C (below 10), and sets performance requirements verified by IS 101 test methods.
ISO 12944
Standards
Corrosion protection of steel structures by protective paint systems. Defines corrosivity categories C1 to C5 that specify how aggressive an environment is.
ISO 2409
Standards
Cross-cut adhesion test. The ISO counterpart to ASTM D3359, rated GT-0 (best) to GT-5.
ISO 2813
Standards
Specular gloss measurement at 20°, 60° and 85°. The ISO counterpart to ASTM D523.
ISO 9227
Standards
Salt spray corrosion testing. The ISO counterpart to ASTM B117.
M
Mandrel bend
Testing
A flexibility test to ASTM D522 in which a coated panel is bent around a cylinder of defined diameter. The film must not crack or detach.
MEK double rub
Testing
A solvent rub test used to detect under-cure. A cloth soaked in methyl ethyl ketone is rubbed over the film; a properly cured thermoset resists it.
Metal temperature
Process
The actual temperature of the part, as opposed to the oven air temperature. Cure time is counted from when metal temperature is reached. Confusing the two is the most common cure error in the industry.
Mill scale
Pre-treatment
The blue-grey iron oxide layer formed on hot-rolled steel. Must be removed before coating, a film bonded to mill scale fails when the scale lifts.
Milling
Manufacturing
Grinding extruded chip into powder of controlled particle size.
MOQ
Commercial
Minimum order quantity. For custom-matched powder shades this is typically 100 kg per shade, reflecting the minimum practical extrusion batch.
N
NCS
Colour
Natural Colour System, a Scandinavian colour standard used alongside RAL for specifying shades.
O
Orange peel
Defects
A regularly dimpled surface caused by incomplete flow-out. Usually traced to film thickness, metal temperature, particle size or excessive gun voltage.
Outgassing
Defects
Gas escaping from a porous or galvanised substrate through the film during cure, producing pinholes or burst blisters. Prevented by preheating the part.
Over-cure
Defects
Excessive time or temperature at cure, producing a brittle film and, in light colours, visible yellowing. Detected by a mandrel bend crack on a film that otherwise looks fine.
Overspray
Process
Powder that does not adhere to the part on first pass. Unlike liquid overspray it can be reclaimed and reused, which is why powder coating approaches near-total material utilisation.
P
Particle size distribution
Chemistry
The spread of powder particle sizes. Too coarse causes orange peel; too fine causes fluidisation and reclaim problems.
Passivation
Pre-treatment
A final rinse stage that seals and stabilises the conversion coating before drying.
Pencil hardness
Testing
Surface hardness graded by the hardest pencil that will not gouge the film, to ASTM D3363.
Picture framing
Defects
Heavy film build around the perimeter of a panel with thin coverage in the centre, caused by field concentration at edges and excessive voltage.
Pinholing
Defects
Small holes through the film, usually from outgassing or from moisture trapped in the substrate.
Polyester
Chemistry
A resin system that is UV stable, making it the basis of all exterior-grade powder coatings. Cured with TGIC or HAA.
Polyurethane
Chemistry
A resin system offering superior flow-out, gloss depth and humidity resistance. Used where appearance is the priority.
Powder coating
General
A dry finishing process in which electrostatically charged polymer powder is applied to a grounded metal part and cured under heat into a continuous film. Contains no solvent and emits no VOCs.
Pre-treatment
Pre-treatment
All cleaning and chemical preparation of the substrate before coating. The largest single determinant of coating life, larger than the choice of powder.
Premix
Manufacturing
Weighing and blending of resin, curing agent, pigments, fillers and additives before extrusion.
Pure epoxy
Chemistry
An epoxy resin system with excellent chemical and corrosion resistance but poor UV stability. Used indoors, enclosed or buried.
Q
QUALICOAT
Standards
A European quality label for architectural powder coating on aluminium, with classes reflecting exterior durability. An approval covering a specific coating system, not a company.
QUV
Testing
Accelerated weathering using fluorescent UV lamps and condensation cycles, to ASTM G154. Reported in hours.
R
RAL
Colour
The German colour standard most widely used in industrial coating. RAL Classic numbers are four digits, for example RAL 9010 Pure White or RAL 9005 Jet Black.
REACH
Compliance
The European regulation on registration, evaluation, authorisation and restriction of chemicals. Relevant to Indian exporters, particularly regarding TGIC.
Reclaim
Process
Recovering and reusing overspray powder. Cartridge or cyclone systems return usable powder to the hopper.
Resin
Chemistry
The polymer backbone of a powder coating, which determines its fundamental properties: epoxy, polyester, polyurethane or a hybrid.
RoHS
Compliance
Restriction of Hazardous Substances. Limits lead, cadmium, mercury and hexavalent chromium in products.
Rust creep
Testing
The distance corrosion spreads sideways from a deliberate scribe during salt spray testing. Acceptance is typically no creep beyond 2 mm.
S
Salt spray
Testing
Accelerated corrosion testing in a salt fog cabinet to ASTM B117 / ISO 9227. Comparative, it ranks coatings but does not predict field life.
Scratch hardness
Testing
Resistance to a loaded stylus, specified in IS 13871 as no scratch exposing bare metal under a 3000 g load.
Shelf life
Commercial
How long powder remains usable in correct storage. Oracle's published storage stability is 12 months cool and dry; IS 13871 requires not less than 6 months below 25 °C and 65 % RH.
Shot blasting
Pre-treatment
Mechanical cleaning by propelled abrasive media. Removes rust and mill scale and creates a surface profile that improves mechanical keying.
Sieving
Manufacturing
Classifying milled powder to remove oversize particles and achieve the target particle size distribution.
Sintering
Defects
Powder particles fusing together in storage due to heat or humidity, forming soft lumps that fluidise poorly and cause orange peel. A real risk in Indian summer storage.
Spectrophotometer
Colour
An instrument that measures colour numerically, enabling objective matching to RAL, NCS or a customer sample and calculation of ΔE.
Substrate
General
The material being coated: mild steel, galvanised steel, aluminium, cast iron or magnesium alloy.
Superdurable polyester
Chemistry
A polyester formulation with enhanced UV and gloss retention for demanding exterior applications, typically specified against higher QUALICOAT classes.
T
TGIC
Chemistry
Triglycidyl isocyanurate, a widely used polyester curing agent. Restricted in some markets, which is why TGIC-free HAA alternatives exist.
Thermoplastic powder
Chemistry
A powder that melts and flows without crosslinking and can be remelted. Distinct from thermosetting powders, which cure irreversibly.
Thermosetting powder
Chemistry
A powder that crosslinks chemically during cure into an irreversible network. All four Oracle Industries product lines are thermosetting.
Throughput
Process
The rate at which parts pass through a coating line, generally limited by oven dwell time.
Transfer efficiency
Process
The proportion of sprayed powder that adheres to the part on first pass. With reclaim, overall utilisation can approach 95 %.
Tribo charging
Equipment
Friction charging, in which powder is charged by contact with the gun barrel rather than a corona field. Penetrates recesses far better and largely avoids the Faraday cage effect.
U
Under-cure
Defects
Insufficient time or temperature at cure. Dangerous because the film looks normal but has poor adhesion, softness and low chemical resistance. Detected by an MEK double-rub test.
V
VOC
Compliance
Volatile organic compounds. Powder coatings are 100 % solids and contain no solvent, so they emit no VOCs during application or cure.
W
Weathering
Performance
Degradation from combined UV, moisture and temperature exposure. Assessed by accelerated QUV testing or by real-time exposure racks.
Wrinkle finish
Finishes
A deliberately textured finish in which controlled surface tension during cure produces a fine, even wrinkle. Effective at hiding substrate imperfections.
Z
Zinc phosphate
Pre-treatment
A conversion coating giving excellent adhesion and corrosion resistance on steel. Typically applied in a 5-stage or 7-stage washer. The pre-treatment used for Oracle's published laboratory results.
How to use this glossary when reading a data sheet
Three habits will tell you more about a supplier than any brochure:
- Every performance number should carry a test method. "1000 hours salt spray" is incomplete; "1000–1300 hrs to ASTM B117 at 75–80 µm" is a claim you can check.
- Every corrosion figure should carry the film thickness it was measured at. Thicker films give better numbers, so the two are inseparable.
- Testing to a standard's method is not the same as being certified to that standard. A supplier who tests to ISO 9227 is not thereby ISO certified, and any supplier blurring that distinction is telling you something.
Oracle Industries publishes all eight of its laboratory test reports in full, with the method and film thickness stated for every value. Download them here or ask us a technical question.