[CIE76] How much of delta-E does this represent?

[rollingcloud]

Using a color meter or spectrophotometer to measure the variation between the area in the red circle and the upper area, what would be the approximate delta-E? I have never used such a tool, but my supplier is saying it's less than 3.0 and is acceptable. But since it's clearly visible to naked eye, it should be greater than 3. Only a couple of parts out of a large quantity have this issue, so I am not convinced that this is a perfectly normal condition. Anyone has experience with plastics and color meter?

 

[IRstuff]

Your photo is looks to be highly misleading, since the upper piece looks to be in shadow, while the circled piece looks to be directly lit. Unless both surfaces are lit under the same conditions, you have no meaningful comparison.

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[rollingcloud]

I agree the lighting is bad. The color meter was using the previous good parts as reference, so it does not have to be on the upper piece. See a good part below, would the yellowing in my original post equivalent to a delta-E of >3?

 

[IRstuff]

Again, this photo is also misleading, since I have no idea whether both images were taken with the exact same illuminant and/or even the same camera with the same exposure conditions.

CIE measurements are very precise and as such, require precise illuminants, i.e., lighting intensity and color; it's not something to be done with a cell phone camera.

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[IRstuff]

As a minimum, both "good" and "bad" parts need to be in the same picture, illuminated with the same lighting to even come close to any ad hoc judgement. Or, both parts need to go through a spectrophotometer sequentially, using the same setup.

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[rollingcloud]

Thanks for the info. The supplier said that the yellowing is due to the plastic compound. I also noticed that yellowing due to polymer chain degradation is typically uniform, the yellowing on my part appears to be different, resembling a pattern of the natural movement of viscous fluids. Does this non-uniform distribution suggest it may indeed be due to the mixing of colorants? The base color for the plastic is tan, so I feel it can be easily appearing as yellowish or brownish if it's not mixed perfectly.

 

[rollingcloud]

this one was taken side by side with the yellowed part.

 

[IRstuff]

Again, you need to have IDENTICAL illumination; one part is nearly directly lit, the other is at a glancing angle. That is not same illumination.

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