I'm thinking of buying an antique fountain pen, but the barrel is stuck to the nib and the section because the ink has dried it shut, and I'm thinking of ways to get it off.
Maybe by using ultra-sound? Maybe by soaking it in water? Or maybe there's just no way?
I don't want to buy it until I'm positive I can get the barrel off.
The pen has a 14k gold nib and is not plated. The exterior of the barrel is plastic.
Prepare a jewelry cleaning kit...
moisten separate squares of paper towel in common solvents and put each in a separate plastic bag. make one each for clean water, water with dish-soap, rubbing alcohol, acetone (nail polish remover) and maybe... dilute ammonia and dilute bleach (but make sure these last two towels never touch each other or follow directly each other when used). Label each plastic bag clearly with a black sharpy. take some dry paper towels as well.
The gold nib is probably your best testing area as you know exactly what it is made of. gold is extremely non-reactive so exposing it to water, dish soap, alcohol or acetone is completely safe. ammonia can dull the shine on gold and bleach can oxidize its outer surface turning it black. either the dull or the black can be buffed away with a dry paper towel, repairing this minor damage. (once again a safety note about bleach and ammonia. do not let them touch each other as they give off a poisonous gas when they combine).
So with your cleaning kit ready, go to the current owner of the pen and ask to run a quick cleaning test. If the owner doesn't agree, he may know something about the unwanted ink that he doesn't want you to learn. In which case, you should probably go find another pen. It the owner does agree,...
Rub the dried ink on the nib across a dry piece of paper towel. If an ink line forms on the towel, this is your base line. A solvent works if it draws a darker line than the dry paper towel.
Repeatedly drag a dried ink spot on the nib across each solvent's paper towel. Between each solvent test, drag the ink spot across the clean water towel to avoid mixing solvents. Once you find a solvent which produces a dark ink colored line, the test is over. The dried ink can be removed with that solvent, so the pen is safe to purchase.
If none of the solvents produce a dark line, then the "ink" will require stronger cleansers than can safely be used around the soft gold and plastic.
I'm thinking of buying antique fountain pen, but the barrel is stuck to the nib and section because ink has dried it closed.
No. Dried ink is not why it's stuck together. With vintage fountain pens, the section has been glued to the barrel with resin. The best technique is to use a heat gun (or hair dryer) to gently heat the barrel/section overlap area until the resin softens enough for you to separate/unscrew the section from the barrel with your fingers. It doesn't take a lot of heat, so start slow and gradually test for sufficient softness in 10-15 second increments your first time, until you get a feel for it.
Do not do the Frank Dubiel "Da Book" thing of using an open flame. He was a labtech and knew how to control heat with a bunsen burner. I, as a once-inexperienced vintage fountain pen collector, can personally attest that you can melt pen barrels over a candle until they're like taffy. The glass-nibbed Japanese celluloid pens (e.g., Spors) can even combust. Please don't ask me how I know that. [facepalm].
The nib and feed may be stuck in the section due to dried ink. The nib and feed are always friction fit into the section because airflow is required for the capillary exchange of ink/air so the pen can write. And if regular fountain pen ink was used, it's just water-soluble dye, so should dissipate with water. But. If India ink was used by accident, the pen is more or less ruined, because any solvents that can dissolve the ink are likely to dissolve the plastic of the feed/section as well.
Do not soak the entire pen because water can contact metal internal parts (such as the J-bar (press bar in your illustration) if it's a sac-filler) and cause rust. Prolonged soaking of hard rubber causes discoloration (black becomes gray). I only do an overnight soak of the nib, section and feed unit after it's off the barrel, and then knock the nib and feed out using a nib block, if I can't just pull them out with my fingers.
A nib block (aka knock out block) is a solid object with a hole drilled through it, where the hole is small enough to securely keep the section from entering, but large enough for the nib and feed to fall through. Using a punch and lightly tapping on the rear end of the feed to push it forward from the back end of section will separate a stubborn feed and nib from the section. Pendemonium, as well as other online vintage pen dealers, offer tools like this, or more specialized tools (like a vac wrench for Parker Vacumatic sac replacement) if you can't DIY your own.
I also feel I should state that the most common issue with vintage pen restoration is replacing rubber bits that have fossilized or gone sticky/soft. So, you will probably want to have a link to the Pen Sac Company, and a source for o-rings and gaskets for your specific model of pen; vintagepens.com is one good source.
See also David Nishimura's article on Pen Repair Do's and Don'ts.
