I'm meeting with a strange and insurmountable problem when polishing. My polishing set-up is pretty unsophisticated, but when it works it works absolutely fine. Basically I work down from file, emery papers, then 4 different grades of silicone rubber polishing drum operating in a Dremel. I finish off manually with a piece of leather (rouge rubbed into the flesh side of a piece of calfskin.) I don't have a bench polisher.

I've had the problem on all of the last three silver rings I've made. The 2 coarser grades of silicone drum begin to polish things up nicely, but typically when I move on to the fine grades, all of a sudden the drum will deposit what looks like a dull gluey streak down the middle of the ring, which then proves almost impossible to remove. I say it's a dull gluey streak because that's what it looks like; it's as if someone has poured a liquid on to the ring which the polishing drum then smears into a noticeable streak with clearly defined edges. The streak seems to occupy mostly the centre of the ring, and usually the edges will retain their polish. Looked at under a 30x loupe the streak doesn't have any thickness to it; it's just a duller area of metal that I cannot for the life of me make shinier.

I say the problem is insurmountable because I haven't yet found a way of completely getting rid of the dull streaks. More polishing with the fine drums makes no difference (often makes things worse), and I'm ending up with rings that I just can't get a uniform polish on. I've a suspicion that the problem might just be fire scale, because a small part of the streak at least appears to have a brownish tinge to it, but I've only had the problem on the outside (not inside) of rings, and the last two rings I've done were dipped in a boric acid solution before soldering to discourage firescale; in contrast the rings I did that didn't have the problem were not dipped in boric acid before soldering.

Any advice would be appreciated.