I didn't explain that very well.
The group of 90T related to the Thomas are from something causing the plate to be made incorrectly.
The plates are made from a set of large negatives called the mask. It's usually a bunch of negatives taped to an opaque paper or plastic sheet. The plate is exposed much like a photograph would be, then developed. If something like a hunk of tape or strip of paper was between the mask and the plate that part wouldn't get exposed and that portion of that color wouldn't print.
I think the 90T and the Seaver/Clemens were both caused that way. The 90T is the most extreme example I've seen. Very sloppy work by the platemaker.
Other cards missing areas of color may be similar, but it's just one way of having missing color in an area.
Incorrect original
Incorrect mask
Bad plate
Solvent/water drips
Debris in the press.
Too much wetting of the plate
Underinking
Damaged/stained paper stock
Misfeed of a sheet
Partial print of the sheet - Impression cylinder not engaged for the whole rotation
Sheet not fed through at all
I think that's it, there could be others I missed.
And some of those have related errors.
Debris in the press can sometimes wrap around the plate, get inked and print what looks like faded solid color.
If there's too little water instead of too little the entire plate can get inked to varying degrees and will also print a light solid layer.
All are pretty cool, but the only one I'd call a variation is the incorrectly made plate.
Steve B
|