Mysterious Polishing Problem

[Aurarius]

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.

[Wallace]

it sounds a little bit like you are talking about firescale - could be wrong. If you stick your item on a white piece of paper, can you see a greyish lok to it.


hints and tips for reducing firescale from a variety of places include:
a little bit from Ganoskin (courtesy Charles Lewton-Brain)


of course there are one or several posts here on Cookson too.

to remove firescale, you need to file it out.

To reduce it's occurrence, a variety of different fluxes that coat the metal are useful. Including Prips, and FM solution (this can be found on Page 25 of Sarah Macrae's book: Designing and making jewellery). Coating the metal prevents the copper from oxidising and forming a coating. Reticulation also helps.

To reduce it on your pieces you can use a cutting polish too. So a Tripoli or any of the popular brands will do it too.


Incidentally, I read and will try and find the reference. There are other ways of reducing it from being forced out, which include cold polishing. So tumbling would do that. Not getting the piece hot when buffing will also help.

I am sure there are others who will give you better information or their experienced points of view too.

kindest regards,
Wallace

[caroleallen]

Are you sure it's not silicone from your drum? I don't use drums but when using radial wheels, if I don't work up from the coarsest to the finest in the proper order, I get a residue. Could you take a photo and show us what you mean?

[CJ57]

Without a photo it sounds like fire stain to me too. Had a bitch of a day with my spoons too, tripoli and rouge will work it off if it isn't too deep or you may have to rub them down again before you start polishing

[Dennis]

Yes Wallace most likely has the answer. If it won't wipe away with a solvent, then it's firescale- The curse of the jewellery making classes. Here's more reading on the subject:

https://www.google.co.uk/search?q=Fi...en-GB:official

Basically it is copper in the alloy oxidising to this dark grey oxide and begins to show more and more as the metal gets mirror like. It can be filed away, or simply disguised by taking the metal to a satin finish, when no one will notice it at all.

You can also disguise it by repeatedly heating and pickling about five times. This creates a thin layer of fine silver on the surface- a process called depletion gilding.

The cause of firescale on sterling, is heating it for too long and using a fierce flame with a strong blue cone in the centre, called an oxidising flame. You can reduce the heating time and close the air hole on your torch a little if it has one, to create a more bushy flame.

You can also coat your work in a flux, especially when annealing. Any flux will do, but a strong solution of boric acid in meths is convenient as it it is cheap and comes off easily in pickle. However the bottle must be kept well away from open flames. Dennis.

[Aurarius]

Thanks everyone for your answers. I'm assuming it is firescale at this stage, although as Wallace suggested it did seem to appear very suddenly when the ring was starting to get quite warm. Carole, I do work up methodically to the finer grades, but maybe I'm assuming it's time to move on when it's not. I will try to take a photo.

I've got to admit that I'm still at the very early stages of learning and the three rings that showed the problem had to be resoldered several times before I got them right. My main problem has been creating a perfect mating of the two ends of the ring blank. The first two rings I had problems with were 4mm x 2mm D-wire; the current one is 4mm x 1.3mm rectangular. I've had a heck of a job with both of these. I only managed to get a perfectly sound solder-join by spending absolutely ages repeatedly filing or sawing through the two ends until they met with no visible daylight anywhere; I know this is the only way to get a proper solder-join. Any tips on how to speed up this process would be really appreciated. Of course the filing and sawing reduced the length of the ring blank so I had to do a lot of hammering on the mandrel and remove material from the inside to get the ring back up to the required size.

One other thing I do find odd is the different amount of time it sometimes takes to get the same thickness of blank up to heat. I use a Proxon minitorch. Using hard solder I've found it can take anything from about 60 seconds to three or four minutes to get the solder to flow. The method is the same each time - use a fairly bushy medium sized flame and heat the piece evenly- but the time it takes for the ring to get reddish seems to vary enormously. This is what has made it difficult for me to keep the heating time to a minimum. Does a ring take less time or more time to get up to temperature once it's already been heated, or does a previous heating make no difference?

Also, is it best to lay solder over the outside of the ring with the join at the top of the ring, or is it better to have the join pointing downwards and lay solder on the inside of the ring? I've found the second method seems to make the solder flow more readily, but then you end up with most of the excess solder on the outside of the ring, where you don't really want it. I'm also aware that solder flows towards the hottest part, so presumably, since heat rises, the bottom of the ring will be marginally cooler than other parts if I've been heating the ring evenly, and you'd think the solder wouldn't then really want to flow down through the join, but it does.

One last thing (sorry to go on). Other than putting the ring in tweezers held in a 3rd hand I don't use wire or any kind of clamp to keep the ring ends from opening up when heating, because I'd assumed that opening up doesn't occur, and if you get a good join it'll stay that way when you heat it. But I'd swear once or twice I've made a perfect join and the join has opened during heating and ruined the soldering job. Is wire-wrapping or clamping necessary/advisable for rings?

Many Thanks!
Mark.