acidic paper t.124:vyp.1(1992:ianv./fevr.)-t.128:vyp.6(1996:noiabr/dek.),t.129:vyp.2(1997:mart/apr.)-t.129:vyp.4(1997:iiul/avg.),t.129:vyp.6(1997:noiabr/dek.),t.130:vyp.6(1998:noiabr/dek.)-t.135:vyp.3(2003:mai/iiun) acidic paper pH pen test foxed covers t.124:vyp.1(1992:ianv./fevr.)