File your edges
First process/phrase off the rank refers to a step in the intaglio method of printing.
When we talk about intaglio plates in a historical sense, they’re made from metal in some form. Copper was widely used for engraving; iron was used for early etching, but copper seems to have become popular for this method as well. Regardless of the metal involved, there’s one thing that needs to be done before the plate is allowed near the press:
File your edges!
A sharp, unfiled metal corner or edge can damage a number of things (or all of them): the paper laid on top to receive the image, the press blankets (which absorb water from the paper and cushion the impact of the rollers), or even, in some cases, damage the rollers of the press themselves. That might sound implausible for a modern metal intaglio press, but I think it could be possible to damage the roller of an early press with wooden rollers.Unlikely, but possible, and then the apprentice who accidentally did it would be in deep trouble.
In any case, it’s not optimal – if you cut your paper, you’ve wasted paper. If you cut your press blanket, that cut mark can impress upon the paper in future printings, which means you either have to not use that section of blanket, or get a new blanket, and they’re expensive. If you damage the roller, that part of the roller won’t give the same pressure as the rest of the roller, and again, that will be visible in future impressions. And the roller is even more expensive than the blanket…
The other good thing about filing the edge is that it provides a ‘ramp’ for the press roller to receive the plate, allowing it to ease under the roller. This helps prevent skipping of the plate or dragging of the paper.
And last but not least, having a smooth edge makes cleaning the plate easier. Any ink on the edges will also print, so the better prepared the edges are, the easier to wipe clean, the cleaner your print will be.
So an intaglio plate is chamfered by filing along each side. Some printers will also round each corner and chamfer that as well. You can even burnish the filed edges to make them even smoother and shinier (must bother to do that some time). Here is the corner of one of my copper plates:
And here is the corresponding part of the image on paper. You can still see the indent of the plate on paper, which is made as it passes through the press:
In the image below, you can see how the plate has probably been filed any number of times to keep the edges smooth:
Above: Daniel Hopfer, The Lovers, c1520, etching
The filing has resulted in the final shape of the etching to be irregular, but this shows that it was definitely more important to the Renaissance printer to avoid damaging your equipment than having a perfectly shaped image.