Re: Filters for 'atmospheric' indoor B&W photography
What "atmosphere" do you want? If you want your photos to look "old" you could try an overlong lens hood (to give deliberate vignetting) plus, if you can afford the light loss, an 80 series filter to remove practically everything except the blue (matching the blue-only-sensitivity of early emulsions). If the light source is domestic tungsten then you could be losing up to 3 stops.
I suggest you try adjusting the percentages of R G and B individually in your digital sample, as that will give you an idea as to what transmission characteristics you would need from a filter to provide whatever "atmosphere" you want.
Possibly some deliberate underexposure (to darken the whole scene) might be worth trying, too. I'd try to get the darkest part of the black circular thing behind the lady jet black, let the other dark parts sit right down on the toe of the response curve and make the mid-tones quite dark. I don't know the metering characteristics of your G6 but I do know the OM4Ti quite well. On HP5 processed normally I'd spot meter from the lady's face and bracket, expecting to underexpose by 2/3 stop from the meter indication to get the effect I've indicated.
If you're not living on the edge, you're wasting space