Microbiology lab questions

Hi, I'm currently taking a microbiology lab this summer (btw, I love this lab it's a lot of fun!), and I have a few questions. They aren't "HW" questions, just me curious wanting to know why (sometimes I think the bane of my existence as I'm always asking the how's and why's behind things, drives my family crazy sometimes.lol.).

First one is regarding negative staining. Why don't you heat fix the slide for negative staining? I know for others, like Gram stain, you need to but what would heat fixing do for a negative stain? Would it cause an encapsulated cell to show no halo?

The 2nd concerns acid fast bacteria. Why are they gram positive? I know the differences between gram positive and negative bacteria, but why are acid fast usually gram positive?

I usually don't think of these questions to ask my lab instructor until hours later, when I can slow down. Since it's a summer lab, we're cramming 3 weeks worth of lab in one week, and I usually don't review what I've done in lab until later on in the day. Inevitably, questions pop up of "Why?" .

Thank you.