L * a * b values for metallic inks?

[viswanaathan_r]

 

[D Ink Man]

Sir,

L*a*b* values for metallics in reality have little foundation.

Because of the nature of metal particles, usually either aluminum or bronze, a spectrophotomer has virtually no ability to accurately and consistently produce consistent L*a*b* numerical values.

Why you may ask? It is because these metal particles go through a process called leafing. The leafing effect which occurs when a true metallic makes contact with a given substrate, is constantly changing because of the mechanism of leafing, the migration of the metal particles to the surface of the ink film.

This leafing and scattering of the reflected light interferes with the spectro's ability to read and transmit data. The leafing can occur from the point of printing to some 72 hours after. And..any disturbance of the printed metallic film will be skewed from any or slight abrasion inflicted upon the printed film.

If you can view the metallic ink film versus a normal pigment ink film using a profilemeter, you will be able to view the same obstacles the spectrophotometer has versus the human eye. High magnification also depicts this.

Hope this helps.

D

 

[gordo]

@viswanaathan_r

Buy a box of corn flakes:

Spread a bowlful onto a table to an even corn flake thickness.

That is what the metal particles of a metallic ink look like under high magnification.

Turn off the lights in your room and then illuminate the flakes with a torch (flashlight) at a 45° angle. Maintain your viewing angle while rotating the torch around the flakes while maintaing the angle at 45°. That shows you how the flakes appear to your spectrophotometer.

best, gordo

 

[viswanaathan_r]

Thank you Sir for this detailed reply. Now, with this info, I can convince my customer who is insisting on Delta E tolerance for metallic ink. Thanks once again.

 

[viswanaathan_r]

Thanks Mr. Gordon, for the very simple yet effective explanation.

 

[Stephen Marsh]

http://www.xrite.com/documents/apps/public/whitepapers/Ca00033a.pdf

http://www.xrite.com/documents/apps/public/whitepapers/Ca00015a.pdf

http://cias.rit.edu/~gravure/tt/pdf/pc/TT6_DimitriosPloumidis.pdf

http://www.inkworldmagazine.com/articles/2004/01/improving-metallic-ink-printing-through-polarized-


Stephen Marsh

 

[fiatlux]

@Stephen...

Corn flakes work for me.

FL

 

[Stephen Marsh]

@Stephen...

Corn flakes work for me.

FL

One extreme to the next I guess!


Stephen Marsh

 

[D Ink Man]

My reply was explained in average layman terms.

If there are any further questions or explanation that can be offered, please do not hesitate to ask. D

 

[dleather]

Now, with this info, I can convince my customer who is insisting on Delta E tolerance for metallic ink.

Exactly what is the customer insisting on?

If you're showing them Epson or Kodak proofs, that's naturally not going to emulate the metallic very well, as those machines don't output metal flakes at all? Or if they have their own spectrometer and are trying to measure, what can they possibly be basing the "control" on? A fifth color spot metallic ink is only going to be at 100%, and only have one value, right? By that rationale (assuming it's properly trapped and not being contaminated by CMY or K), the Delta-E is going to be 0 in every instance. I don't see how this issue can actually come up...