Cracks, crazing, and values
Traditionally, cracks (usually found in cap lips and barrel mouths) were serious flaws that drastically affected the salability of all but the rarest pens. More recently, however, there has been a growing acceptance of cracks, as long as they are stable and unobtrusive, and preferably well-sealed. This acceptance makes sense, especially when the pen is question is going to be used and where functionality takes precedence over a pristine state of preservation. Nonetheless, new collectors should not be tempted to pay full price for damaged examples of pens which are readily available in undamaged condition.
A far more serious problem is deterioration of celluloid pens, usually known as crystallizing or crazing. This deterioration is progressive and irreversible, and will inevitably destroy any pen so afflicted. A key early warning sign is a patch of transparency developing at one or both of the pen's extremities, including the area over the inner cap. The reason why these areas are afflicted first is unclear, but it seems likely that it is because these areas are either thicker than others or are backed with an impermeable barrier (the hard rubber inner cap). As celluloid ages, the byproducts of its ageing are least able to escape into the atmosphere from these areas, and being retained, promote faster deterioration. Some celluloids are significantly more prone to this decomposition than others. Solid, opaque colors are very stable, whereas some of the colorful marbles used in the 1930s by Eversharp (and to a lesser extent, Waterman) are particularly unstable, especially the greens, for some reason. Sheaffer plastics generally hold up very well, perhaps due to the company's innovative celluloid curing techniques.