I am carrying around on my vacation a 1974 reprint by the Visual Studies Workshop of Herbert Denison's A Treatise on Photogravure (in Intaglio by the Talbot-Klič Process). It is available used at a price of $275 (for the reprint) at Amazon.com today, which may put it out of many people's reach.
For whatever reason, this book is one of many scanned by Microsoft as part of an effort to put out-of-copyright works on the web for wider access. A full color PDF version of this black and white treatise is available, and other formats are available also, in a scan from the University of Toronto. It was the 32nd hit on Google.com that yielded a launch page on Archive.org to find a scanned version of the text. I keep forgetting to search there first - they have several other early texts on photography.
A brief biography of Jon Goodman mentions that he carried this slender 140 page reprint around with him during his early studies of photogravure in Europe (though it incorrectly lists the first publication date as 1865 - some thirteen years before Klič perfected the method).
The book presents a complete description of the steps of process in the table of contents:
- The Negative
- The Transparency
- The Gelatine Resist
- The Copper Plate
- The Ground
- Mounting and Developing the Resist
- The Mordant
- Etching the Image
- Photogravure in Line
- Printing from the Plate
- Afterwork on the Plate
- Steel-facing the Plate
- Historical Notes
The text assumes hands on knowledge of traditional silver photography and darkroom work, and perhaps a working knowledge of carbon printing methods. I do find it amusing that these older texts have sections titled Historical Notes. The facsimile edition reprints the 1895 version - some 55 years after the invention of photography. Also, as others have noted, steel-facing is a misnomer, the copper plates once etched are iron-coated electrolytically. There are some modern references I'll dig up to non-toxic (less toxic) approaches to copper plate photogravure - do poke around a bit to find those.
So if you were looking for something to read as you entered the New Year, this is my recommendation.