Selvage markings: Registration marks

Selvage (US English) or Selvedge (British English) is the paper at the edge of sheets of stamps.  You will often see single stamps or blocks with this extra paper attached, and it is usually blank, but there are a lot of markings that can be found in these tiny scraps of extra paper.  Here is a pair of Sudan #35 with brown and blue registration marks and interesting brown bars. 

Registration marks are used to make sure the different colored plates are aligned as precisely as possible.  I have worked in high-volume print shops, and remember grabbing a sheet every minute or so and checking the registration.  You would have to run the paper through the press once to print the brown ink, then dismount the brown plate and mount the blue plate, then feed the whole stack of paper back through and apply the blue ink, doing your best to keep everything lined up exactly.  There are many moving parts in an industrial printing press, and the plates do gradually shift.  If the marks start to get out of alignment, you have to stop the press, adjust the plates, and fire it up again.

If you think the paper jams in your printer are bad, try to imagine the messes that can happen with hundreds or thousands of sheets per minute coming out of a machine six to eight feet long.

Here are a few other styles of registration marks.

The one from Barbados has the four colors at the edge, and if they are not vertically aligned, sheets would probably be thrown in the trash until the alignment was fixed.  To me, it also looks like a classic case of CMYK printing: the bars are roughly cyan, magenta, yellow and black.  In this time period, CMYK was a standard way of getting full color images to print with accurate colors.

The marks on the pair of Portugal postage dues are a "bullseye" style: you can faintly see the paler ink very slightly shifted to the left, where the other two shades of brown hit their marks perfectly, but it was still within acceptable range.  We used simple cross-shaped marks in the print shop where I worked, and all the colors were supposed to hit the cross exactly -- if any color shifted slightly, it would double up the mark and would be very easy to spot, as opposed to trying to look at whatever complex design we were printing and seeing if it "looked right".

Nothing we ever printed had the exacting detail needed for postage stamps.  On stamps, the printing needs to be exact to within a few tenths of a millimeter, especially to make room for the precise perforations which are applied afterward.

Here is a detailed discussion of whether or not to remove the selvage.  It covers the bases well.  Album pages are not designed to handle extra paper: each space is exactly the right size for just the stamps.  But having broken down over a hundred collections over the years, I can say that if you just do what the album pages tell you to do, your collection will look exactly like every other collection.  I always save extra bits, anything that can make my collection stand out a bit.  One of the easiest solutions is to collect one of each plain stamp, but have a nice stockpage every now and then of all the variations you can find.