I was about to post, and my OH said she wanted the pc - so I disappeared for a coffee.
I appreciate that Ohio has give a very good explanation of things - his side of the pond - so hope he won't object to my few words that would have been posted had I not been delayed
It's very interesting to see that whereas CH describes the resist being within the intaglio part of the copper plate - Ohio's description is the reverse, and it has to be said that as is often the case when we speak of methods, differences occur depending on whereabouts you are on the globe.
"probably not without much repeating, verbatim, of Barbara Morris' words, but there seems no doubt that transfers appear to be one of the main processes for creating images in the second half of the C20.
As opposed to straight forward machine acid-etching - the sort that produces multiple repeats of geometric patterns (Greek keys etc.) and the template-machine process - transfer-printing as described by Morris appears to have been complex, and involved taking an image from a lithographic stone (those heavy buff coloured lumps from France).
According to Morris there was a simpler method of transfer-etching (without the lithographic stone), and this appears to have evolved using transfers on which were designs created using acid-resisting inks, the acid biting presumably in the non-inked areas.
Charles Hajdamach 'British Glass 1800 - 1914', describes a similar process involving transfer tissue - possibly less complex than using the lithographic stone.
An image is created on copper - the plate is coated with resist which is forced into the intaglio lines of the image and the plate is then wiped clean. The plate is overlaid with a paper/tissue and the whole thing put through a press, whereby the tissue picks up the image - in the form of the resist - this is then removed from the copper plate, and the tissue is then laid onto the glass.
Obviously there's a little more to it than this rather bald explanation - but hope it 'clarifies the procedure' for you"