It's called How to Start a Home-Based Jewelry Making Business by Maire Loughran. It's chock full (yeah, there's a term I use a lot - not!) of information about transitioning from hobbyist to business owner. It's available online at Barnes & Noble and Amazon. It's also available on Google Books .
It's inspired me to get serious about the business side of my work and I've been researching sole proprietorship versus LLC, taxes, accounting, etc. Ever read so much info you feel like your head is going to explode? That's me.