Like regular cartes de visite, the tintype carte and even unmounted tintypes produced in the United States were required to carry a tax stamp between 1864-66 which can assist in dating of these photographs. A patent for a multiplying back camera was granted to William Southworth of New Castle, Maine on June 17, 1862.The patent was purchased by Simon Wing who had already patented a camera design of his own in 1860.Aside from the speed of its production, the gem was also inexpensive and its small size made it suitable for mounting in jewellery such as lockets and broaches.
Rather then being offered by the studios as a sideline to other photographic processes, dedicated ferrotype galleries became the norm. Wing was granted a patent for an improvement in his camera's design on May 26, 1868 and refinements continued to be made on it (see this Simon Wing camera page).
Many varieties were offered, with at least four different sized oval and also arched openings.
They were described in the trade as ferro holders or ferro matts.
Wing & Allen's Ferrotype Gallery opened at 342 Kearny St, near Pine, San Francisco in 1873 and was apparently run by Bennett G. The studio was located at 523 Kearny St by 1876 and moved again to 521 Kearny St.
The former address was occupied by William Shew from 1879. Allen's death the business was continued by his wife who is listed as the manager of the Wing and Allen studio, again operating from 342 Kearny St from 1884 trading as Allen and Hay, Mrs. Hay but the union was dissolved 28 September 1886 with Mrs. Lalla Allen then formed Allen & Company with Nathaniel Weston in 1887-1888.