This section is from the American Hand Book of the Daguerreotype, by Samuel D. Humphrey. Published S. D. Humphrey, 37 Lispenard Street 1858.
The Daguerreotype plate, prepared in the ordinary manner, should be exposed in the camera a sufficient time to solarize the impression. Then, before it be exposed to the vapor of mercury, expose it for a very brief period to the vapor of either chlorine, bromine or iodine. Then expose over mercury, as usual. I have produced singularly interesting results by this process.