Call it a dustboard, valance, cornice ledge or whatever, it's done. We hung it today in the master bedroom over the sliding door.
It is supposed to mimic a bridge design, with solid pediments on both ends and a softly-curved span which, we're told, is a restful, relaxing shape. (We didn't have a board long enough for the other plan.) This should function to keep the dust off of the elegant Menard vertical blinds we have cherished for eight years.
The valance is constructed from three-quarter inch mungo, (stuff that's left around in the garage or found in a nearby dumpster) so it is green, eco-friendly, earth-gentle, etc. We did buy a piece of quarter inch pine lathe and a quarter-round trim piece. We used paint from the ongoing bedroom project. Total cost was about $10, which is important for a retired couple on fixed incomes.
It screwed in nice and tight to the mounts, but Kathleen's eagle eye saw that, sure enough, it was 1/16th off on the left end. So we shimmed it slightly and now we're on the level and it won't bug us when we wake up in the morning and look at it every day.
We still have some painting to do in the rest of the bedroom, but by week's end we should be done with the spring project and moving on with our retirement.