Spend even a small amount of time in a printshop and you'll quickly realize how much effort press operators put into scrutinizing their presswork through a loupe. The two things they're typically looking for are clear centered rosettes - this tells them that the presswork is in register – and print problems revealed by how well individual letters of type are reproduced in print.
Here's how type printed offset reveals problems:
Normal ink transfer - no apparent problems.
A ghost image appears just behind the primary graphic causing an increase in dot gain. More information about doubling HERE
A smeared ghost image appears just behind the primary graphic. More information about slur HERE
Over emulsified (a.k.a. emulsified, water logged)
Ink is designed to accept a small amount of water (fountain solution) on press. Too much water appears as tiny droplets in solid areas and reduces gamut, image sharpness, contrast, and increases dot gain.
Tailing (a.k.a. misting, slinging)
Too high a solid ink density or ink that's too "long" can cause thin "tails" of ink strands to appear extending behind the primary image causing a loss of sharpness, contrast and an increase in dot gain.
Picking (a.k.a. pinholing)
Small white specks appear in solids. This usually results because the ink tack is too high or there is not enough impression cylinder pressure ("squeeze").
On press, fountain solution acts like a solvent. If it is too aggressive or acidic it can break down the ink that forms the image resulting in presswork that appears muddy and/or "soft." It also reduces total gamut because it reduces overprint trapping efficiency.