I posted this over in Pen History but thought y'all would find it interesting as well. I could never find information on the Esterbrook factory, like exactly where it was. But I have now, and thought I'd share it.
I just put up a page on my blog listing research resources for Philadelphia, including a ton of links to online Philadelphia Directories.
Something else on the page I thought y'all might find interesting is a diagram of the Esterbrook factory in Camden, NJ from 1885. It's from a Sanborn map used by insurance companies.
The red buildings are made of brick, and the yellow ones are wooden-framed.
The location is currently a parking lot across Cooper St. from Camden City School District Office. It was in the middle of the block, along Cooper, between Front and Delaware, on the south side of the street.
Yes, this was before fountain pens. It would be interesting to find another similar map showing what they did in each part of the factory from the fountain pen era and see how the various parts changed.