I'm wanting to glue some polymer clay pieces to metal hair clips. I sanded the area on the metal where I wanted the clay so that it would be nice and poreous, then proceeded with my attempts. First I tried to swish the clay on and bake it, but it fell off. I then tried TLS, same result. Someone suggested E600 glue, doesn't stick worth a darn.

So, does anyone have any suggestions? I'm thinking about using epoxy, would that work?

 try Zap-A-Gap. also, epoxy would work.

 I'm surprised E6000 didn't work for  you. It's one of the best flexible adhesives out there.

I would not suggest epoxy because it is stiff and brittle. As the barrette is flexed the epoxy is likely to crack away from the barrette. I DO think epoxy is great for many uses. I've made 1000's of Swarovski crystal posts with it. But it's too stiff for a barretter that will flex with use.

The only suggestion I can make is to clean both parts with alcohol and to roughen up the polymer clay so it has enough "tooth" to hold.

When your work fell apart, did the glue stay on the metal or on the clay? Or did it separate from both parts? That will give you some indication of what stuck and what didn't.

Thanks! I'll try cleaning both parts.
It stuck to the polymer clay, but not the metal.

 Not sticking to the metal makes it sound like the metal was greasy enough to keep it from sticking. Rubbing or denatured alcohol will clean it up. When we were manufacturing crystal posts We always cleaned our post earring pads before gluing using a q-tip with alcohol. (We used epoxy for the posts.)

Some other conditions that might apply:
Old, stiff E6000 or E6000 that had been frozen might not work as expected.
Bad plating on the barrette - but that would show up leaving flakes of plating on the cured glue.

And if all else fails, there is always wire.  It's not too hard to drill holes through baked polymer clay if the design allows you a place to do it invisibly.  Or you can then go back and cover the holes and any top-side wire with polymer clay to add some textured elements.