Not to add too much confusion here, but if you are thinking about using old processed plates you may well have to remove a varnish layer to get to the emulsion. I believe it may have been common to coat the finished plate with a varnish to protect it. If the varnish layer is cracked (crazed) it may allow water to get to the emulsion and both layers lift off together. The Agfa instructions say to avoid an alcohol based coating and to use a Gum Dammar/Benzole varnish. This would indicate that the matrix is protected by a coating of shellac (one of the few finishes dissolved in alcohol). In fact I just made a trip to the basement and alcohol will weaken/remove the matrix protection. A thin film layer lifted off right away and the matrix layer could be removed by rubbing lightly with a brush. Once dry the color matrix that I didn't touch remained intact but very fragile when touched.