The more uniform the ink film, the better the adhesion, and the smoother the printing surface, thereby allowing for better reflectivity and better brilliance.
The size of the particle influences how much or how easily it will flake off a finished garment or graphic. The finer the particle, the greater the adhesion and the less flaking or rubbing off. In the silver, non-leafing pigments are available and have been used extensively. These particles sink to the bottom of the ink film, which improves adhesion but sacrifices brilliance, as the pigment is not allowed to neatly align itself at the surface of the ink film and reflect light. Some of the golds are also available in nonleafing, but they haven't been as popular or as successful.
Outdoor applications pose a challenge in the form of oxidation and discoloration. There are pigments for screen printing in gold and silver that are specifically treated to resist tarnishing and oxidation. They’re more expensive and, in some cases, are similar to those in the automotive industry and can therefore be exposed to sunlight, salt spray, and more. However, the golds typically are not as tarnish resistant as the silver and, in general, are not leafing. Testing for suitability is an absolute necessity to ensure that the final product will meet customer specifications.
The copper and zinc in gold metallics will oxidize, losing brilliance and, in certain cases, turning green. Aluminum/silver tends to become dull and whiter. This is why color consistency can be hard to achieve. Because the metal flakes are sitting next to each other, on top of the ink film, this leaves small gaps between the flakes—gaps that are bigger when the flakes are coarser. After printing, the presence of these little gaps will cause the substrate or any ink under the metallic layer to affect the resulting color of the print. For example, a blue underneath a silver will give a bluish cast to the silver; a yellow or green underneath a gold will change the shade of the gold.
Another factor influencing brilliance is the purity of the resin used by the ink manufacturer. Purer or clearer ink provides more brilliance. In addition, looking at a metallic print objectively can be very difficult because of the flip-flop effect. Here, looking at the metallic print from different angles can produce results that may not be as visually appealing or desirable as what is seen when looking at the print straight-on.
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