Choose a suitable ink. According to Bertram’s Ink Well, “You should only use ink that is designed for fountain pens, and you should never use India ink. India ink contains a lacquer that will seize the mechanism in a fountain pen and cause permanent and irreversible damage.”
Determine which type of filling system you have. The Aero-metric filling system consists of an ink sac surrounded by a metal guard and pressure bar. Squeezing the pressure bar expels ink from the nib and results in a vacuum that pulls fresh ink into the sac. Some Parkers use a capillary filler, which you’ll recognize by a cartridge that appears to be punctured by a pattern of small holes. Other Parker pens use the proprietary Vacumatic filling system, which has a plunger at the end of the barrel which presses on a rubber sac.
Fill a Parker pen that has an Aero-metric system (the popular Parker 51 is an example) by removing the pen barrel to expose the ink sac. The sac is surrounded by a metal guard with a movable pressure bar on one side. Hold the pen nib over the ink jar and press on the pressure bar to eject any remaining ink. Dip the pen into the ink until the nib is fully covered. Press and release the pressure bar slowly a half-dozen times, until no more bubbles appear in the ink. Remove the nib and, still holding the pen over the ink bottle, squeeze the pressure bar slowly until two or three drops of ink have been expelled. This will clear any additional air out of the filler system. Clean the pen nib with a paper towel.
Fill a Vacumatic pen system by first unlocking the plunger arrangement at the top of the pen. The lock looks like the crown on a watch-winding mechanism. Twist the lock slightly counter-clockwise to release the plunger. Insert the pen nib in the ink bottle until it is fully covered. Press the plunger a dozen times, waiting two to three seconds between each plunge. When the ink reservoir is filled, no more bubbles will appear in the ink bottle. Secure the plunger by pressing it one more time and turning the lock clockwise. Lift the pen nib from the ink bottle and clean it.
Add ink to a capillary cartridge Parker fountain pen–such as the Parker 61–by removing the barrel to expose the ink cartridge. Do not squeeze the cartridge to cause a vacuum. Turn the pen upside down and insert the cartridge into an ink bottle. The capillary action of the cartridge will draw ink into the reservoir. Hold the cartridge in the ink for a minute or so, then slowly remove it from the ink bottle and gently clean the exterior of the cartridge. Replace the barrel and invert the pen to the normal writing position.