Etching question re: Hughes & Rowes book on patination

In Hughes and Rowe’s book, “The Colouring, Bronzing and Patination of Metals”, there is a photo reference on page 25 showing examples of textured finishes (midpage). A note (3.) refers to these photos. For “E” (Y 350) and “F” (Y 351), the note simply reads “etching”. Can anyone here tell me exactly how these two etched finishes were achieved? Or direct me to a resource that might answer this more comprehensively? Thank you.

First you need to find a good resist to make a mask (if you are looking to draw in the mask). Rio sells a few materials for resists. And also Lascaux hard and soft resist. Nice video on it use is

After that its using ferric chloride for copper & brass or ferric nitrate for silver, both are messy but relatively safe and cheap. Then you experiment to find out what you want to build.
Etching also possible by reverse electroforming (electroetching.) Youtubes on that also widely available.

Thank you for your time in answering. I understand and have used the etching process. My question was related more to the particular kind of resist used to create the patterns in the picture referenced.

Hummm… In water chemistry those surfaces look a lot like corrosion cells and often linked to the metallurgy. If i was going to experiment the first thing I would try would be to shut off mixing and significantly bump up the acid (HCl for FeCl3)…no resist. Then if that didn’t work I start adding water soluble organics (molasses?) to limit the motility of the etchant…just some thoughts.
Also, and this is just going with it, adding the resist thinly, and cooking it to crackle.
I had been using the pitch like material but just recently obtained the water based Lascaux hard ( a lot like latex paint) and am just discovering its potential. seems much more robust…