The Blackbird was always the poor relation of the Swan and it may be viewed in the same way today, but the quality was never any less than its more expensive sibling, unlike the Jackdaw which was definitely the red-haired stepchild though it is compensated by the glorious colours of the Visofil.
Who used the Blackbird? I think it was a school pen for the luckier kids but it was also in general use. After all the Blackbird had its own charm and designs which differed from the Swan. That said, this particular Blackbird closely resembles the Swan of the time. The chrome plating goes well with the blue marbled pattern. The pen is in splendid condition, barely marked by use and the passage of time.
In low light the pattern almost looks grey but as the light increases the blue shines through. In full daylight it is an exceptionally bright, intense blue.
Blue marble always shines and yet for some reason it was less popular in its time than the ubiquitous green marble. Fashions change and I suspect it would be the other way round now, though green marble is still well liked.