Magical Crafting?

I'm preparing to run my personal Shadowdark conversion for Robert Conley's Northern Marches. The Northern Marches setting has a magical substance that can sometimes be found and is used in the creation of magical items. I have never run magical crafting before and I envision the creation of magical items as extremely difficult, limited and specialized. Whatever the opposite of OP is – that's how I tend to do things :-)

What are some of the systems or supplements OSR people use and recommend for magical crafting? It could be something a PC could theoretically eventually learn how to do after much training and education. I'm thinking of primarily making it an NPC activity but I want to see what's out there to help me decide how I want to handle it.

I'm looking for a system where it would be arduous and take quite a bit of time and education to learn how to craft. I'm not looking for something where a lower level character could easily whip up a magic sword in his spare time.

Thanks in advance.