Bronzing and Gloss Differential are issue's that sometimes become apparent due to differing amounts of absorption of ink by the paper's coating.
Bronzing is a phenomenon where, when paper is viewed from an angle, part of the image seems to disappear or take on a uniform tone (usually a green/bronze tone, hence the name). It occurs because of some of the ink laid on the paper is not properly absorbed into the coating, instead sitting on top of the page. The effect is only visible from an angle and is generally not a real problem in practical contexts, however when visible it is quite unattractive.
Earlier pigment inksets were the most well known culprits - the Epson 2000P was notorious, and the original Ultrachrome inkset had bronzing problems on gloss and semi-gloss papers. The new Ultrachrome K3 and later printers have pretty much eliminated bronzing as a problem.
Gloss differential is a visible difference in the glossy surface of a print across areas with different amounts of ink or between areas of the page printed on versus not printed on. Generally, it's not a huge problem as it's not easily visible, but it can be visible in direct viewing of the print and can create an unpleasant appearance.
In general, spraying your prints with a high quality coating, such as Hahnemuhle Protective Spray, will substantially reduce or even eliminate gloss differential with typical semi-gloss and gloss papers.
super high gloss papers, the spray does work but will leave a visible
semi-gloss texture on the print and it isn't an ideal solution. The best
option is to try another paper but the problem is inherent in current
coating on high gloss papers and there is no perfect solution at this
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