Do you have to be a thieves guild member to start this quest or can you do it with out being a thief?

It was my experience that you had to be a member of the Thieve's Guild. I had to start the questine and make it through the Honingbrew Meadery quest before Glover and I could talk about his shadow marks.

You can acquire the formula BEFORE receiving the quest from Glover.

Okay thanks, as my guy has nothing to do with the thieves guild will forget that mission. At least i got the recipe, was surprised to see it added another craft-able set of bonemold to the list of things i can make anyway. So I guess it isn't entirely useless if your not a thief.