[There's a moment of consideration. Then, because he hates spelling it out, but he also doesn't know if Wash kind of forgot, and Wash is one of very few people who can follow what Qrow is implying—]

I appreciate the offer, but you've gotta know that chemistry's a prime place for unlucky accidents.

[This is part of why Qrow thinks someone had a very ironic sense of humour picking this for him: sure, there's that it goes against what he's good at and the alcoholic thing, and then there's the fact that it's very dangerous when you are human bad luck.

Also:]

And Lu's busy. It's an option, sure, but she can't be behind everything at the Bureau.

[Not discounting it! Just pointing out that Lucretia can't be guilty of everything all the time, so he discourages assumptions about her without further information.

In other words, he likes her enough that she's Innocent Until Proven Guilty instead of the reverse.]

Magic forge, huh? Interesting.