A Delta E value is meaningful only with a named formula, illuminant, observer, geometry, specular condition, aperture and sample method. Plastic appearance also depends on texture, gloss, thickness and translucency, so a universal pass/fail number is not defensible.
Build the tolerance from real samples
- Select an approved physical master and protect it from light, heat, abrasion and contamination.
- Prepare samples around the visual acceptance boundary using the production resin, surface and thickness.
- Evaluate them under controlled lighting with the relevant stakeholders.
- Measure accepted and rejected samples using the final written method.
- Choose limits that separate those groups with allowance for measurement and process variation.
Name the formula and components
Delta E 76 and Delta E 2000 do not produce interchangeable values. State the exact formula. Total Delta E can also hide an unacceptable direction, so consider limits for Delta L*, Delta a* and Delta b*, or lightness/chroma/hue components, when a particular shift is commercially important.
Check measurement capability
Repeat readings without moving the part, then reposition it and measure multiple parts. These tests reveal instrument repeatability, presentation variation and production variation. The tolerance should be comfortably larger than normal gauge noise; otherwise pass/fail decisions will be unstable. Establish inter-instrument agreement before supplier and customer sites share one numerical limit.
Treat surface and transparency explicitly
For textured or glossy parts, state SCI or SCE and control orientation. For translucent parts, specify backing and thickness. For transparent parts, use transmission conditions and separate haze or transmittance limits where required. ASTM D2244 notes that purchaser and seller must agree on both the permissible tolerance and calculation procedure, and that gloss and texture affect commercial acceptability.
Suitable instrument choice depends on the sample; compare the SD-500, SD-700 UV and benchtop options against the required aperture and mode. Continue with the foundational tolerance guide and supplier color QC.
Last reviewed 21/09/2026 · Level: Intermediate
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