The B&W 30 mm 023 Dark Yellow Glass Filter produces even greater blue suppression and leads to a further increase in the effects of darker yellow filters. When your black and white images are flat, throw on a contrast filter.
Contrast in black and white is generally controlled by yellow, orange and red filters with red producing the greatest contrast. Moderate changes can be accomplished with yellow which can, generally, bump up the contrast just enough to make the difference between a "muddy" print and an acceptable image.