Photography has always been full of multiple variables, most of which effect each of the others drastically. Slight changes in printer settings will make the most precise digital output change. Minor chemical variations in traditional (now called "alternative") photography can make a big difference. Same holds true for one of the oldest forms of photography: photogravure.
Look carefully at the two images below.
The process for the top print involved soaking the paper for only 10 minutes, and using a standard three-blanket setup on the etching press. The image has high contrast, some detail loss, and poor transition from light to dark (gradient).
The process for the bottom print was one in which the paper soaked for about an hour, and an extra sheet of printmaking paper was added on top the the paper/plate sandwich to act as a fourth blanket. The gradients are smoother. There are a couple more steps of mid-tone gray. Some very subtle details start to emerge.
I must give credit to Jon Lybrook for reminding me about this subtle, but important, printmaking trick. It was discussed in grad school, but my work at the time was suited for a standard three-blanket set up, so I forgot about the addition of a fourth "blanket" of printmaking paper until Jon mentioned it to me this January (he saw some of my gravure and said, "you know what will even out your tones...")
in the technical information page (click on Jon's name to get there), he mentions using two pieces of newsprint. When I spoke with him, he suggested using a piece of printmaking paper. I've tried both, and the printmaking paper seems to work better.
I find that I can use the same piece of printmaking paper as the fourth blanket 6 - 10 times before it's too soaked to be effective. I keep a regular rotation of these sheets by letting the wet ones dry, and occasionally stacking them all together and putting weight on top to straighten them out for reuse.