Hi , Had a look at your plates and i am sorry :cry: to say they are not really in my field of expertise, lol If i have any at all , I am not sure that I agree with the comment that plates are rare before the advent of pressing , I have several 18thc plates ,including some 18thc lynn plates so I think we will have to wait for the 19th and 20thc experts to give there opinions ,though the bases look like they may have had a kind of sand blasting as opposed to acid frosting , but hey!! thats a stab in the dark ,
What a great haul though to find so many very useable plates that certainly have some age and quality ,
Good luck with finding out about them
Cheers ,
Peter.