Spencerian 31
A Spencerian sample card (see Smithsonian Libraries Exhibit on trade literature) included a sample of the #31 Pilot Pen among 11 samples--listing it as a "Medium point. Stiff action." This flyer/inflexible nib is not to be confused with the Spencerian #31 Platinum Pen, which is a taper pen, with markings for I.B.T & Cº. Although the companies are the same, the #31 nibs are completely different.
The Blam Nib site says that The Spencerian Steel Pen Co. was formed In 1858 as a subsidiary of the Ivison Phinney Publishing Company, later known as Ivison, Phinney, Blakeman, & Co., and finally in 1869 as Ivison, Blakeman, Taylor, & Co. The New York City-based pen company (Spencerian Steel Pen Co.), was a pen distribution company that purchased its nibs from an English manufacturer, having no factories of its own. The Spencerian pens were made in Birmingham, England, by Sir Josiah Mason for Perry & Co. This explains why many Spencerian nibs have markings for both New York, N.Y. and England.
Versions
There are no additional versions of the Spencerian #31 Pilot Pen in the Chappy's Nibs collection, as pictured below (gray-finish).
Photos
Click any image for a full-resolution photo: 2200 x 640. The image with the ruler is 2300 x 1196.


