craftgrrl | SS Oxidation Question

I have just begun to play with oxidizing my sterling silver using the egg method. (If you're not familiar with it, there's a great tutorial here. However, I have a couple of questions.

1) I oxidize my pieces after constructing them. But I find that sometimes my clear plastic and glass beads get darker along with the metal! Soap and water helps a little, but not much. With the glass beads it seemed as though the oxidation had gotten inside the beads (they were crackled glass). Is there something I can do to prevent my beads from oxidizing?

2) I recently bought some "sterling silver" earwires from Firemountain Gems. But they wouldn't oxidize worth a darn. They turned black in splotches, but mostly remained bright silver. What's up with that? Do they have some kind of anti-tarnish coating on them that wasn't mentioned in the description?

Thanks in advance, everyone! Behind the cut are some things I've been working on.

Aforementioned crackled glass, plus chunky quartz