Ugra Plate Control Wedge 1982
The Ugra Offset Control Wedge 1982© is intended for controlling the analogue plate-making process. Furthermore, it is possible to use it for some evaluations in the proofing process and for printing tests. On the printing plate the following criteria can be evaluated:
- Exposure time
- Exposure latitude
- Optimum resolution
- Rendering of halftone dots
- Continous-tone Wedge - The density values are labeled on top of the continuous-tone wedge. These values are correct for a densitometer that is zeroed without film base (not on transparent films).
- Micro-lines - The 12 patches of micro-lines contain positive and negative lines between 4 and 70 µm. The micro-line patches of the Ugra PCW have the same value as the micro-line patches in the FOGRA-PMS-K-patch (Compared with the K-patch in the FOGRA-PMS Color Control Bar, the Ugra PCW has additional line widths of 4, 25, 40 55 and 70 µm). Therefore, the micro-lines of the Ugra PCW can be evaluated according to the same guidelines as the ones established for the FOGRA-K-patch.
- Halftone Wedge 60 lines/cm - The shape of the dots was calculated and plotted using the FOGRA chain dot model (in order to use a standard halftone dot model, Ugra refrained from using its own model). A moderate chain dot shape was chosen according to the current knowledge about the ideal dot shape. The dot areas where corner link-up takes place are symmetrical to 50 %.
- Slur and Doubling Patches - Slur is caused by a difference in surface speed of two cylinders (plate-blanket or blanket-impression cylinder) and results in a spreading of lines running perpendicular to the printing direction, while lines running parallel with it are not affected. The visual effect is that the perpendicular lines become darker.
Doubling can be caused by register problems between different units on a multicolor press and results in a slightly misregistered overprint of the same image. The visual effect is again the lines of a particular direction become darker. However, contrary to slur, doubling can occur in any direction.
- Small Dot Patches negative and positive - On principle, small dots can be judged in the same way as micro-lines, i.e. it is checked to what extent positive dots are reduced to zero or negative dots have turned to a solid tone.
Application of the Ugra Offset Plate Control Wedge on negative working plates
In contrast to positive working plates, the negative plates the dot areas of all image elements increase with increasing exposure time.