Density is a measurement of how thick a film layer is on a clear or opaque substrate; colorimetry is a measurement of the perception of the color of that layer. They are both affected by the optical characteristics of the film layer but are not the same. A small difference in density may or may not correlate to a visible color difference.
FAQ: Density of Metal Decorative Inks on Aluminum Soft Drink Cans
“My clients are suppliers of metal decorative inks that are widely used in the printing of aluminium soft drink cans. They have “several” customers who, they say, are looking for an instrument to measure “colour density”; a function of film thickness. What they are looking for is an instrument to measure opacity – Generally they do not want the aluminium to be seen through the coating. It appears that the problem is not so much being able to measure, but being able to measure repeatably on the curved aluminium can surface.”
Although your customer is printing a layer of metal decorative ink on an aluminum soft drink can, they are still printing ink on a substrate.
The curved metal surface adds some challenges over ink in a flat paper substrate but the concept is the same. If they can print a “witness coupon” of the same ink on a flat metal surface, this would be contribute to a more repeatable measurement.
Typically, however, they want to measure the final product their customer sees which would be the actual ink layer on the can.
I suggest your client follow this link to information on densitometers , a product line that HunterLab does not carry.
Please note that measuring the density of an ink film layer to the film thickness printed on the surface or concentration of the ink colorant; it does not measure the perceived color. This requires a colorimeter. Depending on the sophistication of the instrument, some densitometers are also colorimeters.
If the ink layer is thick enough (reflection density is high), the translucent ink layer will be perceived as effectively opaque.
FAQ: Density of Aluminum on PET Plastic Film
“Our customer wants to measure the “density“ of a AL layer on PET foil. Do you have any expirience with this?“
The substrate here would be a clear polyethylene terephthalate plastic film with an aluminim sputter-coated on the surface. While this flexible film looks metallic and opaque, the aluminum coating is in effect fine dots with the degree of opacity dependent on the size and surface pattern of the dots.