Fountain pen ink is easier to remove than other kinds of pen ink because it is water-based. You need to act quickly to get the stain out, though, because wet ink is always easier to remove than dry ink. You may have to try a few methods to get all of the ink out, but removing the stain is possible.
Things You'll Need
Towel or washcloth
Paper towels or tissues
Lay a clean white wash cloth or towel on a flat surface. (You can also use paper towels or tissues.) With another wet towel, paper towel or tissue, gingerly blot at the ink. It you press hard, you will force the ink into the fibers. Light and gentle should be your motto.
Soak the stained section of the fabric in cool water for five minutes. (Hot water would set the stain, which you do not want to do.)
Blot again, as in step one, after you have soaked the ink. If ink still remains, spray it with hairspray. This helps release the ink from the fibers. If you don't have hairspray, try some rubbing alcohol. Gently blot again, then rinse in cool water.
Repeat this process as necessary. Pre-treat the area with laundry detergent and wash the garment in cold water.
Recheck the area to see if any ink remains. If it does, you may have to purchase a commercial ink removing product from the laundry section of your grocery store. Do not dry the fabric until you have removed all the ink or it will become a permanent stain.
Keep the area moist through the whole process.
Never use hot water to remove ink stains. It sets the stain!