And my experience with curtains has been limited to straight, rectangular panels, so I was forced to wing it this time.
It turned out like this:
Not too bad! It's not exactly how I had pictured it, but it'll do. I'm actually pretty proud of myself, though the process of getting there was slightly comical (not to mention slow and tedious). I took a leap of faith, and photographed each step along the way -- just in case it wasn't a complete disaster in the end. The process went something like this:
I determined that the width of a roll of waxed paper would be about right for the height of the valance (so scientific!), and cut a piece double the width of the window (72"). Then I marked the halfway point and attempted to draw a gentle curve on one side. Next, I folded the whole thing in half and cut on my line.
Not such a gentle curve after all.
But with a little more trimming it looked passable to me.
Then I fan-folded the whole thing and taped it up to my window to see how it would hang.
That didn't look quite right, so I flattened it out a bit, trimmed off some more and tried it again.
Better. Now I had a big piece of fan-folded wax paper, impossible to lay flat for cutting. So I folded the whole thing in half, wax sides together, and ironed it -- melting it into one very stiff hunk of pattern. But it was flat. Next, I pinned the bulkiest pattern ever used on the fold of my lining and fabric (folded end-to-end) and cut it out. I had to piece my prints first, because I didn't quite have two yards of either one. Funny I never thought to check that before.
Next I marked a new curve line on the pattern for the top layer of the valance. This is where I wish I had only gone two or maybe three inches shorter. I went four.
Repeated the cutting process with the second print and lining.
Next, I pinned both print pieces to the lining pieces, wrong sides together, and sewed the sides and bottom (1/4" seam), leaving the long, straight, top edges open.
Turned both pieces right side out and pressed.
Next, I pinned the two layers together at the top, in reverse order of how they would hang. The shorter top layer behind the longer bottom layer.
I stitched the top together with a 3/8" seam, then flipped the top layer over to the front and pressed.
At this point, I folded the valance in half and pinned it to my window to determine how far down I wanted to sew the rod pocket.
Which ended up being a 1-1/4" rod pocket, 1-1/4" from the top. (Just two seams, straight across. The space between the two panels forms the pocket.) I didn't dare make the header at the top any larger. I think I could have gone a little longer overall with the whole valance. I blame it on the wax paper. It should have been wider.
So that is how a person clueless without a pattern goes about making a patternless valance. (I can just imagine the pattern designers snickering out there. LoL) It would have been a whole lot easier to just buy the valance in the first photo at Bed Bath and Beyond... but then look at all the fun I would have missed! :/