I made a single print of this cover the first time I came to Grand Rapids. I went back to this same location in July where there are three covers in a row each with their own unique nuances, but all using the same markings.
The story behind this particular foundry and design is awesome! Below is an excerpt from an online transcription of the 1891 book, History of the City of Grand Rapids, Michigan, by Albert Baxter:
Frederick Hartmann started at 69 South Front street in 1872, in a small way, a jobbing foundry, doing general work, employing four men, in a room only 40 by 50 feet. In 1879 he added a small machine shop, and took Louis Dietz into partnership in the latter, under the firm name of Hartmann & Dietz, the foundry being still that of F. Hartmann. In December, 1884, the foundry was turned over to the management of Henry J. Hartmann. In July, 1886, the partnership between Hartmann & Dietz was dissolved, and the firm of F. Hartmann & Company organized, with Frederick Hartmann, H. J. Hartmann and Edward Tannewitz as members. In June, 1888, they moved to 270 South Front street, where (in 1888) the Phoenix Iron Works are doing a business of about $17,000 annually, giving employment to twenty-four men.
Even better, I found an ad from 1887-88 Polk's Michigan State Directory for the Hartman Foundry and the headline describes their team as "Founders and Makers" which brought the whole thing full circle.
Henry J. Hartman Foundry Co.
Grand Rapids, MI