Attractively anchor a wire cable into drywall

Question

I want to string a ‘high’ tension wire between two walls, for hanging light decorations on. The word ‘high’ is in quotes because it only needs to be tight enough to keep the wire looking level across a 7' span with a few glass ornaments hanging from it:

Unfortunately I don't think that there are any wood studs for me to anchor into. (The drywall is actually facing iron I-beams that are supporting a catwalk and upper hallway.) Even if there were wood studs, the placement of this wire needs to be rather exact (to match built-in furniture below), so I cannot assume the studs would be in the correct spot.

So, I have three questions:

1. How would you anchor into the drywall (or the underlying I-beam?!) in a way that will provide enough tensile anchor strength (away from the wall), as opposed to the typical shear strength (along the wall) used by picture hangers and shelves?

   • (I found this link testing hanging strength of various mechanisms; if anyone has a similar page for pull strength I would love it.)

2. How would you tension the wire, if you didn't want an ugly turnbuckle tensioner left on the wire?

3. What is the most visually minimal way you can think of to secure the wire? In my ideal world, I'd tear a hole in the drywall, anchor and tension the wire inside, and then patch and paint it so that the wire appears to come straight out of the wall. Assuming I'm anchoring into the exterior of the drywall, though, how can I avoid things like ugly wire clamps and thimbles?
   

Followup:

I originally stretched wire between two eyelets and hung the glass ornaments from that wire. The result was not aesthetically pleasing. (The wires were too thick and noticeable, even well-tensioned they bowed slightly under the weight, and it didn't look good to have horizontal wires in the middle of the space.)

In the end, I hung them straight from the ceiling by:

• throwing together horribly dangerous scaffolding,
• drilling 1/2" holes into the drywall,
• pushing a 3/16" eyelet/toggle bolt up through the hole,
• tying 30-pound test fishing line to the eyelet,
• screwing in the eyelet bolt until it was past the surface of the drywall, and
• filling in the holes with drywall putty, sand and paint.

Hole filled with putty, before sanding/painting.

Full pictures can be found here:
https://picasaweb.google.com/106711366581540292524/HangingGlassWithDuctTape
or perhaps here:
https://goo.gl/photos/QuhyZXAnFKMByUtA9

Answer 1

I'd find mounding hardware with a wide base, then use the 't-bolts' to anchor them (it's a bolt with spring-loaded 'wings' that expand inside the wall to grab the back-side of the sheetrock). The wider the base, the better, as it will distribute the load over a larger area of sheetrock.

As for tensioning, you really do want the turnbuckle, as the cable could stretch a bit over time.

Ikea has some decent systems we've used for curtains.

Oh, and just my own opinion, but I'd find a cable coming straight out of the sheetrock odd, visually. I'd embrace the mounting hardware as part of the look.