The second law of thermodynamics tells us that disorder always increases. Everything is subject to entropy, even fountain pens. Decay and degeneration goes all the way from the hardened sac to casein rot. The first is, of course, easily dealt with, the second is beyond repair.
Not all pens degrade at the same pace. I’ve had high quality black hard rubber Swans in a dreadful state; what was once shiny black now dirty yellow, gold plating gone, nib bent and cracked. Against that I’ve had cheap and cheerful no-name 1920s advertising black hard rubber pens as black as night with their original shine, perfect except for a decayed sac. Clearly there was a difference in the hard rubber because it happens too often to be a freak.
We hear, in the pen boards, about celluloid so decayed that the barrel of the pen is falling apart. I must be lucky because I’ve never had a celluloid pen like that but I’ve had casein Burnhams disintegrating in the same way.
These are consequences of chemistry and time. Other things that can cause major problems come from the user. Pen nibbling or even chewing reduces a pen to a condition where no one will want it. Hard rubber has memory. Heat is enough to trigger a return to its original condition if the chomping isn’t too bad. With some other materials the solution takes longer and is more arduous.
Then there’s the user that puts something in the pen that shouldn’t be there. Artists’ inks and old iron gall inks can thoroughly clog up the works. I have spent hours on a feed and section of a pen left to dry up with ink that turned to concrete.
People drop pens. I understand that. I’m clumsy myself, though I’ve never been unfortunate enough to drop a pen nib-first onto hard flooring. I’ve dealt with the consequences often enough. I understand that some modern pens will shatter. That’s really not my area but I’ve often had to deal with nibs that looked like a propeller. If they’re not cracked they can usually be recovered but it is time-consuming and difficult. There are geniuses who can return such a nib to its original condition. If I can achieve a respectable appearance and a good writer I congratulate myself.
Most pens can be fixed. Sometimes the repair will take so much time that it doesn’t make financial sense. Sometimes I do it anyway. Other times the pen becomes spares. It’s very rare indeed for me to pitch a pen into the trash and when I do it’s invariably a modern pen that cannot be repaired due to its defective manufacture. So even those pens that I can’t repair live on, rescuing another pen by providing parts.
Entropy does destroy many things but fountain pens fight back. Many of the pens I work on are twice as old as I am and there is every reason to think they will still be writing a century from now.