Lapidary thread

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Re: Lapidary thread

Postby Lefty » 09 Sep 2017, 09:48

Made a few now, making plain bands from sterling silver is easy. Silver is actually pretty friendly for soldering. What is not as friendly is copper.

I bought some copper sheet to practice cutting out shapes with the jewellers saw. Silver is not expensive per se but copper is cheaper and it cuts and bends very similar to sterling so it's good practice material. Copper is actually a beautiful looking metal when polished up, it's just that it's more prone to oxidising than silver. This means the surface condition won't last (mine still looks good a couple of weeks later but has been sitting in a cool, dry environment all that time) and it also means that soldering can be tricky. Solder does not like to flow across an oxidised surface, hence the use of flux. Copper oxidises so fiercely when hit with a flame that the metal very quickly develops a thick crust of oxide, preventing solder from creating a solid join. Plumbers solder copper all the time but they are working with copper pipes rather than delicate bits of metal - they can drown it in a heap of flux and blast it with a torch like a rocket engine, no problems there.

But tiny, delicate bits of metal are prone to being overheated and possibly melted so you tend to go slow and careful - and slow is what you cannot do with copper because it oxidises so quick. The much smaller amounts of flux used in jewellery break down in the heat rapidly compared to a large amount used on a copper pipe join and the metal oxidises before the solder can flow.

But I've soldered it successfully now, trick seems to be as much flux as you can get onto the piece and heat it FAST.

Made a very simple piece by cutting out a teardrop shape from copper sheet and soldering a fine silver bezel to it (yes, some different metals will solder to each other) and then setting a little chrysophrase cab in it. For an early attempt I was happy enough with it.
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Re: Lapidary thread

Postby HBS Guy » 09 Sep 2017, 18:48

Yeah, copper is a pain to keep nice and shiny.

I have a neat little brass scale. I took it off the wooden base and took the actual scale to a place that does brass polishing. Was quoted $90–120 to clean and polish it then cover it in a varnish.

Might give them the art nouveau jardiniere to clean, polish & coat too. It is bloody big and bloody corroded!
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Re: Lapidary thread

Postby Lefty » 13 Sep 2017, 08:17

Yeah, brass is much the same is copper in solder as far as soldering goes, since it's usually about 60% copper I think, with the remainder being mainly zinc. But it resists tarnishing better than copper. Maybe I should do some brasswork, the silver merchants in Sydney I buy the silver and copper from also sell brass.

Can't polish it yourself with brasso or something? Or is it too corroded?
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Re: Lapidary thread

Postby HBS Guy » 13 Sep 2017, 11:01

Lot of work!

BTW—forget Brasso! Go to UltraCheapAuto, they have tubes of cleaner/polisher for cars that is WAY better than Brasso! The antique shops use it to keep their copper/brass articles polished.

The brass oil lamp I saw—lots of green verdigris all in finicky, hard to reach places which is why I will take it to the brass polishing place, get it done then get it varnished, easy.
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Re: Lapidary thread

Postby Lefty » 17 Sep 2017, 06:56

I think Brasso actually contains a fine abrasive, you'd have to be careful using it one something that has fine detail anyway.
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Re: Lapidary thread

Postby HBS Guy » 17 Sep 2017, 07:04

All polish would have some abrasive, Brasso more than Silvo tho. Even toothpaste has some abrasive in it!

Some people polish too much, get the nickel showing through on silverplated articles.
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Re: Lapidary thread

Postby Lefty » 17 Sep 2017, 07:44

Actually, some don't contain particles big enough to be really considered what we would call an abrasive in the usual sense. With the oxide polishes such as alumina, cerium, tin etc there is continual argument as to how the polishing action really occurs. No one has yet invented a machine that can allow us to see what is happening to a surface (of a gemstone) during polishing and the same oxide of two very different particle sizes can produce a very similar looking polish.

While there has to be at least some abrasive action from the polish particles, it appears that in many cases the oxide + friction creates a chemical reaction and an infitismally-thin layer at the surface "melts and flows" for want of a better term. British scientist Sir George Beilby discovered this property in gemstone polishing in the 1930's, with American scientist Earnest Fairbanks backing this up later on.

Since then, many people have tried to discredit the notion of polishing creating a "Beilby layer". However, the issue just keeps on coming back up because it is obvious to anyone who has been involved in lapidary long enough that there is indeed something there. Someone was complaining about it a little while ago on one of the lapidary forums, trying to re-polish a stone for a customer and having trouble because the already-polished surface simply would not behave like a raw, fine cut surface ready for it's first polishing. While there was much to-ing and fro-ing, in the end nearly everyone agreed that polishing seems to create a surface layer with characteristics that are slightly - but noticably enough to cause headaches - different from the underlying material. This isn't really what we would expect if the polish was entirely the result of ultra-fine abrasion by inert particles.

For myself, I will happily claim to have actually seen the so-called Beilby layer, through very powerful loupes, much more powerful than I normally use for lapidary work (dunno why I bought what amounts to a low-powered, hand-held microscope, way in excess of what is needed for faceting but anyway I did). Just like Beilby, who noted a very particular scratch pattern, polished the surface with oxide until a perfect polish was achieved and scratches no longer visible even with magnification -and then etching the surface with acids and recovering the identical scratch pattern - I have actually seen similar. Seen a particular scratch pattern left by the fine cutting lap and polished the surface with cerium oxide until the scratches were entirely gone. But on close examination with said very powerful loupe, at particualr angles the exact same scratch pattern was still just visible but the scratches now had the appearance of having been "filled in with liquid glass". It really didn't appear that it was just the last vestiges of the original scratches that hadn't quite been removed, there definately seemed to be something filling in the scratches, as though polishing had created an amorphous layer - similar to glass or opal - which had flowed into the scratches and filled them.

Just thought I'd chuck that out there :bgrin - this isn't really an issue with metal polishing, there's only two grades in jewellery polishing and both probably do function as fine abrasive (though a precious metal polish called "Rouge" in the jewellery trade is in fact iron oxide).

Btw, you can buy all of this stuff for not that much from Bunnings. I have a cheapie Chinese made bench grinder from Bunnings - think it was about $60 - took the grinding wheels off it and replaced them with coarse buff on one side charged with "Tripoli" which is an aggressive pre-polish for metal and the other a soft muslin buff charged with Rouge for the final polish. The adaptors for screwing on the buffs, the polishing compounds - all available from Bunnings. I think this set up would polish a significantly large brass, bronze, silver or copper item very quickly. It's way more than what I actually need for little items like rings. True, you still won't get right into small, tight corners but if you have a lot or ornamental metalware, it might be worth looking into.
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Re: Lapidary thread

Postby HBS Guy » 17 Sep 2017, 07:54

Yeah, reminds me I bought a lump of polish and a soft polishing head just for polishing brass. Will find my cordless drill and give that a go on the brass and copper jardiniere I bought recently (to go on the glove box of the hall stand.)
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Re: Lapidary thread

Postby Lefty » 17 Sep 2017, 08:06

I think you should be able to get a variety of polishing fittings to go in a cordless drill. My flex-shaft (a Dremel with a long, flexible drive shaft and a light hand piece used for carving and jewellery work) takes heaps of fittings that can get right down into nooks and crannies. Not sure how small they make them for drills but a regular Dremel even without a flex-shaft is a very handy little tool for multiple applications around the house. Probably can rig up something to go in a drill that will get right down into tight spots.

Just watch things like felt polishing bobs and little buffing wheels for drills and hand pieces - the felt or brush hairs wear out and expose the metal of the little tool shank. And while you already know that tool steel is rather harder than brass, copper, silver etc, there's nothing like the joy of experiencing having polished a piece to near-perfection - and then ripping a fucking great scratch across it as the steel bit pokes through the worn out felt or brush :b
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Re: Lapidary thread

Postby HBS Guy » 17 Sep 2017, 08:23

Ahahahaha yeah, nah this wheel is like 10cm diameter, will be OK.

The brass polishing place first soaks the piece in acid and that should get rid of the green verdigris I reckon.

Might try vinegar (on the jardiniere.) Lots of articles on how to clean brass, comes down to making a paste of vinegar and baking powder. I think the acid in the vinegar does the work of getting rid of corrosion, the baking powder acts as mild abrasive. Put the paste on, working it in, leave for 20 minutes, rinse, buff dry.

Heh, I have a phosphoric acid based sanitiser (used in the dairy industry) for sanitising brewgear, bet that will shift corrosion alright :jump
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Re: Lapidary thread

Postby Lefty » 17 Sep 2017, 08:40

Yeah, should be ok then, just be sure to keep the metal hub of the tool away from the item you're polishing.

At the club they used a dilute sulphuric acid based "pickle" as it's called, for cleaning silver after soldering, which coats it in oxidisation. A number of jewellery-making blogs said all they use is household vinegar and table salt at the rate of 2 tablespoons of salt dissolved in 1 cup of vinegar. This is all I've used since I started mucking around with jewellery making and I can tell you that it works almost as fast and every bit as effectively as commercial solutions - with the added bonus that the ingredients are non-toxic and as cheap as chips!

Copper develops the most unbelievably thick crust of oxides when you solder it but the salt and vinegar pickle strips it back to shiny metal in no time. I've found it works most effectively when it's about the temperature of a hot cuppa and you immerse the entire piece but it does still work when cold, just takes longer. I think you could paint the solution over the piece with a paintbrush, might have to do it a couple of times, rinse and quick scrub but I think it would work without much effort at all. Just be sure to wash you hands thoroughly, the salt and vinegar will be toxic after cleaning the brass and having absorbed the metal oxides from it.

I think the phosphoric acid would work as well, just keep your eye on it to make sure it doens't start etching the metal.
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Re: Lapidary thread

Postby HBS Guy » 17 Sep 2017, 09:13

Yup, will dilute it HEAPS if I were to use it. I need to bottle most of the supply I have and sell it while still keeping a lifetime supply for myself (5L say making 10L of sanitiser, 40 x 250ml bottles with flip top lid.)
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Re: Lapidary thread

Postby Lefty » 26 Sep 2017, 08:23

Did you give it a go? Just a little dab in an inconspicuous spot to test?
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Re: Lapidary thread

Postby HBS Guy » 26 Sep 2017, 10:08

Nah, got a problem with inner ear, balance gone, nausea, get a head CT scan tomorrow.
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