When considering a buy, some things to consider:
1. Condition counts. The closer a pen is to its original state, the more it’s worth.
2. Rarity. Other things being equal, a rare pen or rare color sells for more than more widely available ones.
3. Manufacturer. Other things being equal, there are two, possible three tiers of desirable manufacturers. They are Eversharp, Parker, Sheaffer, and Waterman’s,—the big four. In the same league are Conklin, Conway-Stewart, John Holland, Swan, and many other smaller companies. Second tier pens may write just as well, but are valued less by collectors because they are perceived as not as well made. Some are Diamond Point, Eclipse, Eagle, Esterbrook, Gold Bond, and Wearever (a separate file discusses Wearever, often consigned to “third tier” pens.)
4. Age. Some older pens are worth more, others that are newer are worth more because they have some other quality. In general, pens from before 1930 are worth more, while pens from 1960 through 1980 are valued lower. (Note: “Vintage pens” are often defined as pens made 50 years or more ago–but this is arbitrary.)
5. Color. In general, colorful pens are worth more than black ones, while multicolored or mottled pens often are valued more then one-color ones. Before about 1925, all pens were black and made from hard rubber. The first colored pens mixed black and red hard rubber (rare, desirable), yellow and black hard rubber (more desirable), or even blue and black hard rubber (even more desirable). With the advant of cellulite, colors became brighter and the range increased.
6. Size. In general, large pens and very small pens are more valuable then “average” size pens.
7. Nibs. Gold nibs, italic nibs, and broad nibs are the most desirable. (Note: gold nibs are tipped with iridium so they won’t wear away—so gold itself is an affectation. Stainless steel nibs last just as long, and write just as well).
8. Overlaid pens. Some early pens had sterling silver overlays, and some of these rare pens are among the most valuable and rare.