Thanks for the link Conrad. So that is why the set is very dull instead of shiny because it actually has no silver in it. I can't find any other markings on it other than that so I guess there is no way to trace the manufacturer or find the date of manufacture. Still I think it's pretty even if it's not silver plate. I guess then all that's needed to keep it clean is to just wipe it off occasionally.
A bit more involved than that. First wash with phosphate and scent free dish soap, then you use equal parts of glass cleaner and vinegar and using a cotton ball you wipe it down and dry off with a soft cloth. Then you apply the silver polish and buff to a nice shine. It makes even German silver look nice.