gandolfi,

At the risk of being a wet blanket, I have to say I think the plates have more value unopened than any artistic value you might get from them, even with your prodigious skills. They are likely seriously fogged from age.

That said, you won't need a yellow filter with the Ilford plates. 'Auto filter' means a yellow dye was incorporated in the emulsion.

Since you have limited materials to experiment with, it would be handy to get as much information from as few as possible initial tests. I have an old 4"x5" exposure test film, meant to go over a 4"x5" negative in an enlarger. It has an exposed circle with pie slices of different densities and corresponding suggestions about exposure subtraction. If you load a plate with something like that on top of it, you can give the plate what you are certain is over-exposure and then back off the exposure on the next plate to try to match what you learned from the test exposure. Something to keep in mind about many of the old recipes is that they will actually lose density if they are seriously overexposed -- until they 'flip' into reversal mode (solarization.) Remembering that will make it less confusing to interpret your exposure tests.

d