The most obvious reason for using multiple pens is to ease the strain on the hand during long periods of writing. A change of pen can extend that time considerably.

I use the different pens for diffferent reasons. The Montblanc seldom leaves the house; my Waterman Expert II and Lamy Safari Petrol are the ones that go on tour most. My Monteverde Invicia (don't let the name fool you, the pen is made in the USA) is quite heavy, so it gets taken out a bit less. Apart from the weight, the Monteverde and the Lamy both have green inks. Lamy Petrol ink is used in the Lamy, and Waterman Harmonious Green is in the Monteverde. I call it "Uncle Henry Green" which fans of the film A Good Year will appreciate.

The Waterman currenly has Waterman Absolute Brown (which used to have the more glamorous name, Havana), but the bottle is nearly empty and next time I'll fill it with Organic Studio's Edgar Allen Poe Raven Red, with is a reddish, dried blood brown.

Last autumn, I bought a bottle of Montblanc John F Kenney Navy Blue ink, which is a wonderful rich blue, tending to the blue-black. However, my son gave me a bottle of the luxurious Iroshizuku asa-gao (morning glory) blue for Christmas, so I am using that. It's darker than it sounds (and darker than it looks on most websites), and flows beautifully.

So, what does one look for in an ink? Aren't they all the same?

• Colour - Rich? Pale? Good contrast on the paper you're using?
• If you're using a flex nib, you'll want an ink that gives good colour variation to accentuate the variations of the line.
• What's the viscosity like? Not all nibs flow the same; some are sensitve to inks of higher viscosity. My Waterman doesn't like J. Herbin Café des Iles, for example, while other pens run it with no problems.
• Some papers don't like wet inks, but the drier ones may perform well
• Does the ink dry fast enough for you? Left-handers want an ink that dries fast to minimise the risk of smearing as they write.
• Some people have need of "bullet-proof" inks that won't run or wash off. Some documents need to be signed with "permanent" inks.