Digital BW, The Print

try what I may I cant get rid of the lack of smoothness between the 
tones in the cloudy sky section of a landscape shot. There's no point 
in posting a jpeg for you to see 'cos it looks good on screen even at 
100% view but prints out like - i'm not even sure how to describe it -
'mottled' isn't exactly it but its close. This problem is most 
evident in the area where a darkish cloud texture meets the lighter 
sky texture.

I did my scan and most of the initial corrections in 16bit and then 
some in 8. I'm working with Win98SE and PS7 and an 1160 printer with 
MIS sepia>neutral inkset on photorag.

One symptom which may provide a clue for solving the problem, for 
someone, is that I had Layers for darkening/burning in  the top of 
the image and the corners. The problem was excessive. Then I 
eliminated each of those layers (lighteninig the image segments) and 
the problem reduced or just became less evident

I also have a High Pass sharpening layer - could that be it ?

I just looked at Image>Histogram and find it pretty "comb" like - is 
this it ? Is it 'posterization' ? Should I go back to the 16 bit scan 
and try to do more there before converting to 8 and printing ?

thanks
Frank