The stamps were printed at the Government Printers (Oficina Impresora del Gobierno) in Mexico City. Apparently, another printer was responsible for the later printings of the stamps, but from the same plates, with the first delivery occurring on November 20, 1857. Very little is known about the actual printing of the stamps, as it appears that the records do not exist anymore. It is, for example, not known exactly how many stamps were printed of each denomination. It is possible that A. Villegas engraved and printed the first three deliveries, and that the Government Printers printed the remaining 16 deliveries.
Three kinds of paper was used for the 1856 issue:
- First a hand made, plain wove paper, which shows no mesh when held to the light.
- Second, a hand made, lineal wove paper, showing lines and dots when held to the light.
- Third, a machine made, wire wove paper, showing a diamond pattern when held to the light.
The medio real stamps were only printed on the first two kinds of paper. The third kind, the wire wove, was in use from at least January, 1858, possibly delivered from the printer in late 1857. Most stamps, if not all, were printed on this paper from this time on. This paper is sometimes referred to as being porous - it is also generally thicker than the first two types of paper.
The medio real stamps were not printed on wire wove paper, but all the other denominations were. When printed on this wire wove paper, the paper grain is always vertical. This is true for all the 60 subject plates, at least. Stitch watermarks are obviously only found on the machine made wire wove paper.
The medio, cuatro and ocho reales of the 1861 issue were printed on paper with horizontal paper grain. Many reprints have been printed with the paper grain vertical, giving them away.
The ink used in the printing was mixed when needed, and sometimes the mixing was not done very well. When the ink was applied it was not consistent, resulting in over- or under-inking.
The resulting color was also dependent on the wetness of the paper at the time of printing. This gave rise to many color shades in the finished stamps. Color can even vary within one sheet. When the paper was too dry the result was a dry looking, light color. When it was too wet the result was a wet looking, deeper or darker color. If a sheet was wetted unevenly it is easy to imagine that the color of the stamps printed would be somewhat different looking, though they were printed with the exact same ink.
Another factor in the resulting color is the fact that the plates were not wiped properly, at times. If a new batch of ink is applied to a badly wiped plate, the resulting color will be some shade which is not 100% the same as either the old or the new ink. It is therefore clear that almost any shade of any of the colors is possible.
As a consequence of these many factors in producing color, it is worth noting that color alone is not a good indicator of plate or printing number. It is perhaps better to use color as a positive or negative indicator after you have used other signs to determine plate or printing. It is unfortunate that color is used by the main catalogs to distinguish some stamp varieties. It would often be more precise to use the plate number. As an example, I'll mention that the dos reales in the emerald shade is only known from plate I. It would be better to refer to the stamps as being from plate I, in the emerald shade, as opposed to just using the color.
Printing the stamps.
Much of what is discussed here is of course speculation, since very little is actually known. However, 150 years ago there were few choices regarding how to actually perform the printing of the stamps. The most common tool was the manually operated hand-roller press.
The basic operation was as follows: the printing plate was placed on a flat surface, called the bed, thus giving rise to the term flat bed printing press. The plate was then covered in rather thick ink, which was made more fluid by heating the plate. The ink was worked into the engraved recesses with the use of a brayer, a roller similar to a rolling pin used in everyday baking. The brayer was probably made of rubber, or at least rubber coated to avoid scratching the plate. Once the ink was distributed evenly, the plate was wiped clean of excess ink using a piece of cloth. The pressman then wiped his hands on a block of whiting, a chalk like material that absorbs moisture. He would then wipe the plate with his hands, working the ink into every recess of the plate. This process requires some skill, though it may sound easy enough.
Once inked in, the plate was then covered with a sheet of moistened paper. Another person usually did this, since the pressman was pretty much covered in ink. The paper was often covered with a piece of felt or similar material, to ensure the paper would be pressed into close contact with the ink filled engraving. Now the pressman would turn the press by hand, moving the plate covered with paper and felt between two rollers, thus applying pressure to the paper, which in turn would pick up the ink. Once the whole sheet had passed through, the assistant would remove the printed sheet and check the result. If the sheet was satisfactory, it would be placed on a stack, with clean sheets of paper or cardboard between each printed sheet. Later, when the sheets were dry, they would be gummed and ready for use.