If the frizzen was sparking already, perhaps you used wheel weights which melt around 450 F and while a bit too hot is a lot closer than molten pure lead. The ripples also slow down the flint as it travels across the frizzen and will reduce or stop sparking. If you have a fine stone, 6" bench grinder, that is about the right curvature for a Siler frizzen and you can dress the face smooth with it. Deep hollow in a frizzen will do the same thing. I have an original East India lock that looked like someone had used to small of a flint in it for quite some time. It had a deep hollow in the center of the face and would not spark. After grinding most of the hollow away, it now sparks
cheers Doug