What Is Color?
Color measurement is the evaluation in which the CIE L*a*b* coordinates are determined by measuring the sample with a spectrophotometer and the total color difference (ΔE) is calculated compared to the reference color.
Purpose of Color
The purpose is to verify that the color is within acceptable limits relative to the reference or standard and to monitor color change after aging.
Which Products Is Color Applied To?
- Paint and coating surfaces
- plastic parts
- Textiles and leather
- printed packaging
In Which Sectors Is Color Used?
Standards Related to Color
- ISO 7724 serisi
- ASTM E308
- ASTM D2244
- ISO 11664 (CIE kolorimetri)
Color Conditions
- Illuminator and observer
- Defined in standard (e.g. D65 illuminant and 10° observer)
- Geometry
- d/8° (sphere) or 45°/0°; should be stated
- Brightness included/excluded
- SCI veya SCE kipi belirtilmelidir
- Color difference formula
- ΔE*ab veya ΔE00 (CIEDE2000); belirtilmelidir
Equipment for Color
- Spektrofotometre veya kolorimetre
- White and black calibration plates
- Renk referans panelleri
- Conditioning room
Sample Requirements for Color
- The surface must be clean, dry and flat
- The coating must be fully cured
- Measuring geometry and mode must be kept constant
- Reference panel and sample must be measured under the same condition
Duration of Color
Typically 1 day.
Color Procedure
- 1The device is calibrated.
- 2The illuminant, observer and geometry are selected.
- 3The reference is measured.
- 4The sample is measured at a defined number of points.
- 5L*a*b* values and ΔE are calculated.
- 6The result is reported by specifying parameters.
Color Acceptance Criteria
The acceptance criterion is the maximum ΔE value given in the specification.
Evaluation of Results
ΔE values cannot be compared without specifying the formula; ΔE*ab and ΔE00 give different numbers for the same pair. For metallic and pearlescent coatings, single-angle measurement is not sufficient; multi-angle measurement (goniospectrophotometer) is required.
Color Report
- Standard applied
- Illuminator, observer and geometry
- Measurement mode (SCI/SCE)
- L*a*b* values and ΔE formula
- Reference definition
Accreditation
EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.
Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.
Scope and authorisationsRelated Regulations
- Paint, plastic and textile specifications
Paint and Coating Testing — What Does This Testing Field Cover?
The section below describes the field that the Color test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.
Paint and coating testing measures the adhesion of a coating to the surface, its mechanical durability and its resistance to environmental effects. Because a coating is a thin layer, the results depend both on the material and on the QUALITY OF APPLICATION; the same paint gives an entirely different result over a different surface preparation.
This dual dependence is the most important knowledge in the field. A coating failure usually arises not from the paint itself but from the surface preparation: oil residue, insufficient roughening, an oxide layer or moisture. Coating tests therefore assess not only the product but also the process, and the results are used for process control.
COATING THICKNESS is a recurring variable in the field. Many durability results relate directly to thickness; a thin area becomes the starting point of corrosion. Thickness measurement is therefore reported routinely alongside the other tests and is usually taken at several points — thickness falls at edges and corners, especially on complex geometries.
Three approaches are used on the adhesion side, each giving different information. The tape test is fast and suitable for field use but is a coarse scale. The cross-cut test shows behaviour at the intersections of layers. The pull-off method produces a numerical strength value and is the most suitable for comparison.
On the mechanical side, flexibility (mandrel bending), impact resistance, hardness, abrasion and stone chip resistance are measured. Stone chipping has a special place in automotive: gravel striking the coating under real road conditions is simulated, and the result is assessed according to whether the coating continues to protect the base metal.
On the appearance side, gloss and colour difference are monitored NUMERICALLY. Colour is assessed with a colour measuring instrument rather than by eye and the colour difference is expressed as a number; this makes it possible to compare different lots and different suppliers.
On the durability side, accelerated ageing (xenon arc, fluorescent UV), humidity, condensation and salt spray are applied. The result is assessed with scales for blistering, rusting, creep from a scribe and loss of adhesion; these scales are defined in separate standards and the report must state which was used.
In industrial processes such as powder coating and electrophoretic coating, the curing cycle (temperature and time) is what determines the result. An under-cured coating looks good but has poor chemical resistance and adhesion; oven profile measurement is therefore part of coating quality control.
Method groups in this field
Thickness
Dry film thickness by magnetic and non-magnetic methods; multi-point measurement and assessment of the distribution.
Adhesion
Tape test, cross-cut test and pull-off adhesion strength.
Mechanical strength
Mandrel bend flexibility, rapid deformation (impact), pencil and scratch hardness, Taber abrasion, stone chipping.
Appearance
Gloss measurement, colour difference calculation, orange peel and surface defect assessment.
Environmental durability
Salt spray, humidity, condensation, xenon arc and fluorescent UV ageing, chemical and stain resistance.
Assessment scales
Scales for blistering, degree of rusting, creep from a scribe and loss of adhesion.
Commonly confused in this field
- A coating result depends on the surface preparation; even if the paint itself is good, a poor preparation gives a poor result.
- A durability result without a reported thickness cannot be compared.
- The tape test is a coarse scale; numerical comparison requires the pull-off method.
- Colour cannot be assessed by eye; numerical colour difference measurement is required.
- An ageing result without a stated assessment scale cannot be interpreted.
- If the curing cycle is incomplete the coating looks good but its durability is poor; the oven profile is part of quality control.
Which decisions these results support
- Paint system approval and supplier selection
- Process control of the paint line and lot acceptance
- Supporting outdoor and automotive durability claims
- Detecting defects arising from surface preparation
- Monitoring colour and gloss consistency lot by lot
Related Tests
Frequently Asked Questions About Color
Is ΔE 2 a good result?
It depends on the context. Which formula (ΔE*ab or ΔE00) is used, which measurement geometry is chosen and the limit given by the specification are decisive. Two formulas produce different numbers for the same pair.