Let's start
with an anatomy lesson, and then go on to the mechanics.
Clip and cap are, I hope, obvious. There are various sorts of
clip{LINK}, some better than others. The derby is the bit of the
cap which holds down the clip-- if flatter, it is also called a tassie
or a jewel. The band is not entirely decorative, as it
(hopefully) reinforces the mouth of the cap to prevent cracking, or at
least prevents cracks from spreading.
The point is commonly called the nib (I'll bet I even do it a couple of
times on this site), but the nibs of the pen are actually the little
round bits at the very end of the point. These are hard metal
fused to the point, which act to both protect it from the abrasive
effects of paper and to define the width of the line made. As
a note of historic interest, this part was known in bygone days as the pen, and the
rest of it was the pen-holder.
The tines are the part of the point to either side of the
slit. They are seldom spoken of, except in case of disaster
when they get bent. At the top of the slit there is often a
breather hole-- on flexible pens, its real function is to stop the slit
ripping longer in the course of writing.
The feed is the real guts of the pen. I describe more of the
function of it below.
The section is the bit you actually hold onto. The point and
feed are both mounted into it.
The joint isn't really a part of the pen, it's just the border between
the section and the barrel. It is, however, a useful anatomical landmark
The reservoir in most pens is a sac, and the sac is a
bladder made out of some kind of (semi-) durable material-- most
commonly rubber, with silicon making in-roads as a replacement.
Occasionally, as in piston-fillers and eye-droppers, the
inside of the barrel is itself the reservoir. Either way,
it's where the ink lives. The very fact of a reservoir is
what gives a fountain pen its name.
The barrel is the body of the pen which hangs down into your pocket
when at rest and lies on the back of your hand in use. It's a
protector for reservoir and filler mechanism, and has some bearing on
the balance
of the pen (which, if you think is unimportant, try writing several
pages of notes with a golf pencil). It also gives you a place to
put the
cap when
you're writing.
MECHANICS
The reservoir of the pen, regardless of how it fills, is effectively a water-tight chamber except for one
small exit. This hole is a channel in the feed; it is very
small, and it becomes narrower at the end where it interfaces against
the point. The business end of the channel is so narrow that
the surface tension of the ink holds it in place, while distributing it at
the same time to the end of the slit in the point. If this
slit is too wide, or is flexed until it opens too much, the tension
will actually hold the ink away from the nibs, and the pen won't work.
The real trick of the feed, for which we thank Lewis Waterman's
efforts, is to allow air in even as it lets ink out, for if it didn't,
the vacuum which would develop as the first couple of drops came out
would hold the rest of the ink inside. The feed's channel is
arranged to let air in only as it's needed, keeping an equilibrium of
pressure.
Once the point touches down on paper, or anything else, the same
surface tension which had been keeping the ink in place attaches to
that surface, and the ink tumbles down the feed. It is
regulated somewhat by the return flow of air, the size of the slit, and
the contact area of the nibs, but the pen won't have any objection to
putting all its ink down in one place if you leave it sitting in
contact. On most paper, there's not enough absorbancy to
cause a big blot, but newsprint or a cotton shirt will draw the ink out
fast enough to cause alarm.
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