"2 leggotype half-tones (1st patent) from photographs of the moon. William Augustus Leggo, and The Graphic Co., produced the original cuts. One of the earliest uses of relief half-tone in the United States, this example may be preceded only by Leggo’s first work in Canada. Both of these illustrations use random dot pattern half-tones, which Leggo rarely produced."–Hanson Collection catalog, p. 5
The method was to take a glass plate negative, varnish it and when dry coat it with a thick coating of bichromated gelatin, exposing this to light and then soaking it in water allowing it to swell based on its exposure. While still damp take a stereotype of it and then produce an electrotype from that for printing. Next Leggo patented “Granular photography” in Canada in 1869 and in the US in 1871. It utilized both random dot and line screen halftones. Leggo produced the first halftones in a weekly paper, the Canadian Illustrated News (1869 – 1872) and in a daily paper the New York Daily Graphic in 1873-74. The process was primarily photolithographic, though some examples 1869-1870 are printed in relief.