Ideally, pressure is applied evenly across the surface of the paper. However, if a patch of color is too large, and the pressure not even enough, there could be unfortunate variations in shade. Letterpress companies recommend that the maximum area of an image be no more than 8 by 10 inches. Another problem caused by uneven pressure is broken lines if the text is smaller than 6 point.
In letterpress, one color is applied at a time. Care must be taken with lining up re-runs using different colors; the process of alignment is called registration. It is difficult to get a lot of small elements correctly registered. Elaborate designs with intertwining colors should be avoided; bold shapes with a single color are preferred. Thin outlines to a shape do not reproduce very well in letterpress -- these are best thickly drawn for an unbroken image.
Letterpress does not reproduce subtle variations in shading very well. Again, this has to do with the problem of applying pressure consistently. This kind of effect is best achieved with offset lithography. It is also difficult to cover a dark paper with a light color. Choosing the correct color of paper is important -- letterpress works best with dark colors on light paper. It is also very difficult to build up a color by applying different ones to the same area; mixing colors on the page in this way can be very unreliable. Letterpress works at its best with single colors placed next to each other.
In earlier times, an embossed effect in letterpress was regarded as undesirable and the smoothness of paper with handwriting was the ideal. Today, with letterpress mainly being done by small art presses, or for high-end stationery, slight indentations are considered a charming and desirable feature of the process. However, care must be taken that these do not appear as ugly bumps, spoiling the image on the other side. Letterpress requires a careful choice of weight of paper stock to avoid this problem.