When buying a fountain pen, it may be on impulse. Or possibly you have given it some thought.
The range of pens made over the last millennium is extensive and as one would expect, quality, style and durability vary greatly, and not only by make (as with other products manufacturers tried to capture a bigger slice of what was always an extremely competitive market) but also by the period in which it was made.

Buying for everyday use
When buying a fountain pen for everyday use, the following factors should be considered: -

Type of nib preferred.

If you like nib which will give a variation of width to your stroke, pre-war Swan and Conway Stewart produced many pens with nibs which were long and quite flexible. These produce variable strokes dependant on the pressure applied to the point. Do not be put off by a dull muddy looking texture of a pen. This is due to its composition (hard rubber), which was used in the manufacture of early pens and which deteriorated over the years due to damp conditions.

For a firm point look out for a Parker '51' or '61'.
For a very durable 1950's pen with interchangeable nib facility, look for a Parker'45'

Collecting.
Decide on a theme.
Suggestions -colour, pattern, make, size or time period.

Colour
Compare the colour of the cap to the barrel. As noted above some of the early coloured pens were made from materials, which were affected by damp, and merely the moisture of the fingers will cause the barrel to darken whilst the cap remains bright.


Pattern
Many beautiful patterns were produced, particularly in the 20-30's but previous caution applies.

Make
Unless you concentrate on a minor manufacturer the number of models produced is vast and it is advisable to select a sub-category.
The exception to this could be where a maker produced a model and over the years reintroduced it in an updated design. An example of this is the Conway Stewart 'Dinkie', which was first produced in the
1920's and reissued in an updated design through to the 1950's.

Size.
Very large and very small pens are difficult to find. Platignum produced some small attractive pen and pencil sets. Later Conway Stewart Dinkies can be found but the pen is rather fragile and many could be in poor condition. A large pen, The Magna, by De.La Rue was produced around 1936

Timeslot
Each decade produced attractive new models but for obvious reasons the materials used in many pens made in the 1940's was not of the highest quality.

Whatever the theme, condition is important. In most cases, an overhaul will restore the pen to good working order and internal parts and nibs can be replaced, but surface defects, worn threads, and splits in the lip of the cap should be avoided where possible.