Walls – Hanging artwork on plastered brick

Given that it's an exterior wall you've probably hit brick.

This would explain both why you've not found a stud - there aren't any, and why the nail only goes in 1/2" - 1" - you've hit the bricks.

Given that the plaster is crumbling, the simplest solution would be to drill a hole with a masonry drill and use a screw (or screw hook).

If you want to hang a lot of things on this wall then it might be a better idea to install some sort of rail - either a traditional picture rail or a more modern alternative and hang the pictures etc. off that.

Sometimes it's the simplest jobs that can be the most difficult. I'm willing to bet that its the summation of tiny errors leading to a visible flaw at the end. The question you want to ask is "How do I mark and drill a hole exactly where I want it to be?" (For a given value of exactly)

The answer to this question (and many others) is: Make a jig or paper template. Even if you're only doing it once, making a jig or a template is essential for precise work.

For this particular job, a paper template will probably do. Trace the outline of your hook (and holes) onto a sheet of paper. Now, at your leisure, using compass, straight-edge, GPS, and Lasers, find the center of the holes. Even if you just eyeball it, you're still more accurate than doing it on the wall, as you're working at a desk or table with good lighting and a comfortable working position.

Now, photocopy that sucker!

Cut it out, tape it to the wall, and start the drill hole with a small nail or even punch it with a nail set. You don't want the drill "walking" away from its start position. Go in with a small bit next. The idea is that the tool will do all the work so that you can concentrate on keeping that drill level, and on center. Go to your 1/4 inch bit for the plugs, and clean out the hole.

Remove paper, insert plugs, and you're golden.

It may seem like a lot of work, but the results are worth it.
1) Generally, you can't be accurate working vertically, so figure out a way to do the detail work on a flat surface. 2) Always start a drill hole with a nail or punch. It will always walk away when you power on the drill. (This is quadruply true on metal or hard plastics.)