I recently switch over my Epson Stylus Photo 2100 from matte black to photo black inks so I could do glossy or semi-gloss/pearl prints. However, I noticed that my prints were displaying a really unfortunately problem. In certain dark tones, the texture was fuzzy, blurry, or basically reminiscent of an impressionistic painting rather than display the detail that should have been there. My suspicion landed on my use of the print head alignment utility, especially the last part of the test which involves choosing the least grainy patch for different print densities. I always had trouble discerning which of the patches in the #3 column was supposed to be least grainy, they all look equally bad.
I probably compounded things by running the print head alignment utility using photo paper instead of plain paper. Also, it is recommended that high speed printing be turned off, something which I didn't make sure of. Hence, I probably managed to put in totally wrong settings for this part of the alignment test.
Trying to get back to a reasonable baseline has been problematic. From a support chat with Epson, it seems as if the alignment settings are actually stored in the printer, but I couldn't find out whether there were a series of printer button presses which would reset the printer to default. In the end, it seems that the only "solution" is to uninstall the printer driver, reinstall, set up the default printing options to disable high speed printing (turned off finest detail, and smoothing for good measure), and run the utility again and try to stick to the default numbers, (8,8) for the vertical line test, (4) for the horizontal banding test, and (4,4,4) for the graininess test.
Update: The actual problem was the fact that the paper could not absorb the ink fast enough leading to coalescence. After a lot of experimenting, I found that by using a different media setting (Watercolour paper at 1440dpi) and reducing ink density by 15%, I could limit the coalescence. The print quality is slightly reduced and the colours aren't accurate any more, e.g. red prints as orange. This requires a profile for the ink+paper combination which I managed to achieve using the ColorMunki. The final results are more hue accurate but the density is a bit higher than I am used to. The detail still seems to be there in the shadows but requires quite a lot of light to see. A bit more experimenting with media setting might be required in order to get better results.