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yf
08-23-2006, 12:47 AM
I need to repair a silver candelabra.

It is a tubular arm. The end, which terminates in a tapped nut broke off.
The nut is what the candle socket screws into.

I want to reinforce the broken piece with copper tubing and solder it with silver bearing soft solder.

The silver is very thin (almost like heavy foil) and the joint has very little surface, so I don't want to try silver soldering, and risk melting it.

What type of flux would be best cosidering that I wont be able to clean it off the internal surface?

Any recomendations for solder?

Any other pertinent advice?

I have experience with soldering copper, brass, and steel, but have never had to solder silver before.
I also have had some mixed results soldering stainless.

TIA

Evan
08-23-2006, 01:11 AM
Silver is very easy to solder with almost any type of solder. The silver bearing solders will work fine but I am a bit worried about the flux. They usually have a very active chlorine based flux core and that could pose a corrosion problem later. If you can find some low temp silver solder with no flux then use some rosin electronics flux and you won't have to worry.

stuntrunt
08-23-2006, 04:56 AM
you should normally be able to silver solder it without any problems. A lot of preparation is needed though...

First, check if it hasn't been repaired with leaded solder (when heated to its melting interval, the solder will 'alloy' with the silver locally, reducing the silver's melting point and so burn a hole through it).

Secondly, tha copper in the silver alloy will attract oxygen, forming an oxide which shows as duller greyish patches just underneath the surface. To solve this problem, take some Borax salt, dissolve it in demineralized water ('till you get some thickish liquid) and cover the whole candelabra with it.

Build a corner with some fireproof bricks in which the candelabra will fit and heat the whole candelabra with a big, soft blue flame (depending on the size of the project, use a butane soldering torch or a standard roofing torch)

When everything is hot enough, the borax will become glassy (and will protect your silver from oxigen)
Then apply the solder and let it cool (take care, solder always runs to the hottest places. If there are places where you don't want it to creep, 'contaminate' th place with a mixture of polishing compound and light machine oil)

When cool, place the candelabra in battery acid that has been diluted to 10to30% with water. If you heat the acid slightly, it'll eat off the borax a bit faste.

All it'll need now is some buffing with jewellers rouge on a soft woollen buff.

Hope this helps if you haven't already solved your problem...

J Tiers
08-23-2006, 08:11 AM
The smaller the joint area, the more you need silver solder. It is stronger.

You can use a low melt type like "sil-flo", etc, but they don't match silver as well as the higher melting types. The main issue with thin sikver is local overheating..... if this is your first silver-soldering job, might not be a good idea.

Also, if there are OTHER joints , a high melt may open them up due to the required heat.

Metla sculpture folks use graduated melting point solders to do complex assemblies so they can solder another joint close to an existing one.

The downside of a low melt non-silver-solder is joint contamination and the inability to ever get it properly fixed later. But you almost certainly won't open any other joints.

ASparky
08-23-2006, 06:32 PM
The only other gotcha I will add is that many lead based solders and even some of the silver will change color at a different rate to the silver. Over time the joint can become darker or lighter than the rest. Cleaning will usually but not always bring it back to a near match.

yf
08-24-2006, 12:50 AM
Thank you for your replies.

Color matching is not a concern because the joint will be hidden by the base of candle holder/cup when it is screwed on the arm.

I don't want to risk silver brazing, because the metal is so thin and the joint so small, that It will probably melt before the solder flows.

I intend to make a reinforcment of copper tube that will slip inside the arm and also hold the broken stub in alignment, and use a silver bearing soft solder and rosin flux.
These have a melting point of less than 600 F.

With the reinforcemnet, and the increased joint surface it provides, I think that if dropped again, it will break in a different place or maybe just bend.

Its incredible how thin the silver is. It looks about as thick as extra heavy duty AL foil, but is very stiff, probably from cold working.

Thanks again for you advice.

stuntrunt
08-24-2006, 05:49 AM
I have no idea as to whet the candelabra look like and how they are made, so the following might not apply...
Using softer solder will make future repairs a horror...
Try using at least nickel silver (alpacca or whatever the correct term in english is), asthe colour difference to the silver isn't as great.
If the silver is so thin, the candelabra were originally almost certainly filled with some shellac mixture. Can you not use this to glue the pice in place after you soldered a rod to it? Beware, the shellac is not resistant to dishwasher temperatures... (dishwashers are the main reason for knifeblades to separate from their silver handles)
If possible, put a note in the base stating where your solder seams are and which product you used. It will ward off disaster durig future repairs...

If I were you I'd try silver soldering... If the base material is 925 silver, melting temperature is between 800°C and 850°C. You can obtain jewellers solders without cadmium that have a melying interval of 600°C-650°C
And if you take care to heat a large area with a soft flame, the silver'll be all right.

Another thing to consider is the value after dodgy repairs (I'm not accusing you of anything :) )

Maybe it is worth it to look here for someone Who'll do a professional repair:
http://www.silversmithing.com/

Your Old Dog
08-24-2006, 07:32 AM
This may look like a utterly stupid solution because I don't know exactly what you're working with but let me offer it up.

It may be that you don't need all that structural integrity for a candle holder. Most exoctic handmade hunting knives have their handles held in place with 5 minute epoxy purchased at the hardware store.

If of the two pieces you have, one is a hollow type tube and the other is such that a protursion like a screw or rod sticks out of it you can put a about three tube diameteres of mixed epoxy in there, sink the stud into the epoxy and hold the two pieces together.

5 minute epoxy does not harden like glass and that's why it works so well.

Chances of you going in with a soldering iron and repairing a candelabra and repairing the old joint not knowing what the eutectic curve is are pretty slim. You'll likely end up with a mess.