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Silver soldering, I still don't get it.

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Bill Brehm15/07/2013 02:10:41
5 forum posts

Hi Everyone,

I joined this site some time ago because you had more information that any place I had found on silver soldering. I read post after post, learning more and more, and I thought I was starting to understand it.

That is until tonight. I'm trying to make a brass automobile frame. I know it's not steam, or train related, but you're the only ones with any answers. I didn't have a piece of material thick enough to make it, so I just made 2 pieces of 1.6mm X 300mm long X 7.6mm width which I would simply sandwich together. I cleaned, and fluxed the joint. Had drilled and pinned it together for alignment. I use two small vice grip pliers to hold it together and also keep it off the bricks, and proceeded to heat it up. The ends soldered up nice, but when I got to the center I couldn't get the solder to run into the joint. It just sat there as a silver ball. The metal was red hot, the area was turning black, it was warped so bad at that point there wasn't much point in going on with it, and it sill wouldn't run.

Is there a practical limit to how much flat area you can solder together? How do I keep it from warping?

I'm using an acetylene Smith Silversmith torch, with a small tip (2.6mm) that gives about a 100mm flame, and easy flow solder (620C). I don't know if I need a bigger tip for even more heat faster, or to tin it all first, and use small screws to hold it together.

If you have any ideas I'll try it once more before just taking the loss, and get the material I need, but what fun is that?

Thank you,


JasonB15/07/2013 07:31:50
22555 forum posts
2634 photos
1 articles

I would say your small torch took too long to get the work upto temperature and by that time the flux was exhausted, getting it bright red and then going black with oxide would seem to confirm this.

Also there is a risk of the metal expanding and the gap between the two opening up so the solder can't fill the gap.


FMES15/07/2013 08:41:12
608 forum posts
2 photos

Hi Bill, It does sound as though the flux had lost its effectiveness by the time you had reached the middle of a rather long joint.

I would have been tempted to use a normal propane torch witha reasonable flame spread, but first what pickle are you using? Silver soldering needs to be much cleaner that you would at first think, Normal soft soldering preparation is not enough, the pieces need not only to be squeeky clean but chemically clean as well.

My prep would be to warm the job, immerse in the acid pickle, wash off under water with a scotchbrite pad, and repeat, then without excessive handling, flux up and secure then start heating gently along the length of the job.

The flux will dry and then 'melt' and you can see it 'cleaning' the job - if you see any black appearing at this point - stop, the job isnt clean enough or you have already cooked the flux by applying too much direct heat.

When the flux starts to 'run' the job is almost ready for the solder - it is normally a dull red in colour at most, but normally the solder will run before that.

It is important not to apply direct heat to the solder, if the job is hot enough the solder will run better than in soft soldering just by touching it to the job.


Mike Young 215/07/2013 10:21:40
7 forum posts

Hi Bill, I'm wondering if by your description you had it too hot, silver solder is a low-melting point joining compound. It could be that you had the parent metal too hot which means the solder efectively "boils" on contact forming the "ball" you described. Also brass being the lovely material its is oxidises faster the hotter it gets and also some of its constituent ingredients melt, mainly the zinc, and you get that horrible greyish smoke and "soot" on the job.

Again its only my experience, Good Luck !

Mike Young

CuP Alloys15/07/2013 10:33:24
45 forum posts

Hi Bill,

Silver soldering is a very simple process but if you do not stick to the principles of the process you will not succeed.

1) Oxy-acetylene torches in the hands of inexperienced model engineers cause more problems than they solve. The flame is too fierce and localized. The tendency is to not to heat the joint evenly and get it all upto temperature. If you create cold spots the alloy will freeze and not flow.

2) It is difficult with oxy-acetylene to get the heat pattern in a joint that encourages the capillary flow essential if you want successful joints

3) Using propane will overcome these difficulties . It will give you better control over the heat input.

4) You are perhaps adding to the cold spot by holding the work in pliers - a big heat sink

5) Excessive local heat and overheating can/will destroy the flux. Use a long life flux.

6) Heat the components not the solder.

7) Don't use scotchbrite or grit based products for cleaning. They can leave behind residues that the flux (essential for cleaning the joint) cannot remove and lead to pinhole leaks.

8) Pinning the work together removes any joint gap for the solder to enter. Maintain the gap by inserting a piece of foil between the components.

For more info go to Select "Introduction to Brazing" and "Best Brazing Practice" It explains the basic principles of the the process, the whys and how- tos for success.

Silver soldering is basically a simple process. Stick to those principles and you will be successful. Deviate and you won't be.

Success is round the corner!




maurice bennie15/07/2013 11:04:44
164 forum posts
1 photos

HI Bill are you using the right silver solder? these are the melting points of jewellery grade silver solder

ie for assaying.

EASY 705-723

MEDIUM 720-765

HARD 745-778

All of these can be used on brass ,copper ,and some iron,and steels .but are very expensive.There are others to be had called silver brazing rods,a lot less silver and cheaper. Ifyou have TUBAL CAIN hand book on page 6.3 there is a list of all grades of silver brazing alloys and their melting points As all previous posts very good advise ,in silver smithing ,big jobs ,bushy flame, small ie jump rings needle flame .Fluxes I have used are DIEWERSOL ,BORAX ,and fof silver ARGO-TECT(this stops fire stain)

Good luck Maurice

maurice bennie15/07/2013 11:31:22
164 forum posts
1 photos

Hi Bill again, See(Workshop Practice Series No 9.

ISBN 0 85242 845 6 NEXUS Secial Interests. Also ( MODEL ENGINEERS handbook). by

TUBAL CAIN .A mine of information ,It s not let me down yet


CuP Alloys15/07/2013 12:21:42
45 forum posts

Hi Bill,

You are not hallmarking so forget hall marking grades of silver solder. They have a minimum silver content of 68% and higher melting points than necessary.

Use the low melting range, more readily available, 55% silver alloy to do your work. It conforms to ISO 17672 Ag 155 - melting temperature 630 - 660 deg C

Suggest no bigger than 1.0mm dia rod.

Tubal Cain book is excellent, but outdated. Some of the alloys featured MX12, Easiflo, Argo flo are no longer available due to EU legislation banning the sale of cadmium bearing silver solder.



JasonB15/07/2013 13:03:26
22555 forum posts
2634 photos
1 articles

Don't confuse the guy with Jewellery solders, he said he is using Easyflow and stated its 620deg


Its a Jewelers torch he has not their solder

Edited By JasonB on 15/07/2013 13:04:16

Ian S C15/07/2013 14:10:17
7468 forum posts
230 photos

Some where in the deep distant past I seem to remember something about copper, ans its alloys and acetylene, but can't remember any more, anyone enlighten me? Ian S C

CuP Alloys15/07/2013 14:29:26
45 forum posts

HI Ian,

You can embrittle certain grades of copper by using the blue part of the flame. Any oxygen in the copper is converted to steam causing cracking at the grain boundaries.

For ease of mind use oxygen free copper eg C103 and C106.


Lambton15/07/2013 19:15:20
694 forum posts
2 photos

Copper Acetylide is chemical compound of acetylene gas and pure copper it is formed if copper tube for example is used to join acetylene tubing. Copper acetylide is explosive and can cause serious injuries if it ignited.

It is essential to keep pure copper away from acetylene gas and I would be cautious about any copper containing alloy.

There is no danger using an oxy acetylene flame to silver solder copper.

Do a Google search for copper acetylide for a full explanation.



oldvelo15/07/2013 19:34:18
294 forum posts
56 photos

Hi Bill

Lots of good advice offered in this posting on the technical issues to bee observed when silver soldering.

Like all welding and brazing it is a process that requires some manual dexterity to get the best results.

My advice is to address the way you manipulate and hold the torch.

Hold it gently as if using pencil or an artists brush and not tightly gripped like a hammer.

The arms held away from the body like a bird about to fly not crushed into the rib cage.

Keep the flame of the torch on the part to be solderdered and control temprature by moving the torch tip away while keeping the flame on the molten metal.

This will allow the metal to "Freeze" while it is protected from oxidiseing.

DO NOT wiggle the torch from side to side to control the temprature and expose the molten metal to the atmosphere.


Stub Mandrel15/07/2013 19:52:09
4315 forum posts
291 photos
1 articles

Personally, I wouldn't expect to solder such along piece of brass 3/16 wide, 1/16 thick and a foot long by silver soldering it and still get a usable final result.

For such a small, but long and thin workpiece, the small acetylene flame will be too hot and concentrated. The best advice here is to use a cheap propane /butane/propane mix blowtorch 'aiming' along the work to spread the heat ahead of where the solder is applied, but unless it is clamped or jigged at intervals along the whole length, expect something less than straight as a result!

You should get some success by pretinning with soft solder and sweating the two parts together. Use a decent active flux, 'walk' a pair of clamps alternately along from the end where you start the sweating and clean off every trace of flux, or it will turn green. This won't work with silver solder.

My advice is buy some 1/8" brass strip, it's not expensive in that size. Save silver solder for chassis joints and the like where precision heating to avoid damaging other areas and good strength from small joints are what you will need. Use soft solder to add 'decorative' parts where strength is not an issue and you want to avoid breaking the earlier silver solder joints. Soft solder can be used after silver solder, but don't silver solder where soft solder can contaminate the joint.


Bill Brehm15/07/2013 20:57:44
5 forum posts

Wow, I didn't even think my post would be up until later today. So much information I had to take notes as I read. I hope I have address everyone. I'll just paste my notes.


That's exactly how it went. It got red, and then you could just see the gap opening up. I gave up at that point.


I have since learned that most people seem to use the propane and get great results. I only went with the Smith torch because I already had the tanks, regulators, and hoses. My pickle in an in house brand from Rio Grande. It's sodium bisulfate.


My flux is called “Handy Flux – for low temp brazing” made by Lucas Milhaupt, and it seems to turn black even when I get a good result. I can never get it to run clear. Light brown is the closest to clear I ever got.

Mike Young

It's all pink, black, and brown and looks terrible. I pulled it out of the scrap box this morning, set it in the pickle for a few hours. It still looks terrible.


It's just air/acetylene, no oxygen, but I think you are right. I do spend some time, probably not enough, heating the entire piece, and once ready I just concentrate on one spot some small distance from where I will place the solder. My thinking was that the heat would just radiate out, melt the solder, and done. So I should never really stay on one spot?

I knew they would soak up a lot of heat if I was to try to work right next to them. Still it's one more thing to change. I'll wrap the part with wire next try.

I use steel wool to clean the parts.

The foil to space the pieces would be brass or copper, and just a small strip every few inches. Is that what you mean? I have foil, so I'll do that.


I looked at my order again. I'm using “Extra Easy” which melts just a little below “Easy”, and it is expensive. Especially during this learning phase. They have a brass solder that is about 30% cheaper that I might switch to, and a copper solder that is just plain cheap, but has a really high melting temperature.

Ian S C, Eric, Keith

I didn't know about the copper/acetylene problem. I'll look into that. To be honest, I'm not really sure if I can legally have acetylene in my basement. So switching to propane might be required anyway.


This is what my wife told me to do in the first place. After tomorrow I'll either have a nicely soldered frame, or an order for more material. Considering how much work and frustration this has been so far, next time I need a certian thickness, that's what I'll get. All in all it probably cost more in wasted solder and gas than the metal plus shipping would have cost.


I cleaned up last nights disaster. The front of the frame didn't solder well like I had thought. My larger of the two pliers was used on this end. The rear third, to my suprise, went together good enough for my use. I only need to add some solder to where the vice grip was.

From what you have told me, here is what I'll do. Pickle, and clean all the surfaces. Place small strips of foil along the length. Flux, and wrap it in two or three places with wire. Get out my propane bottle, and try it again. If I can use my acetylene torch with propane, I'll get a bigger tip. If not I'll have to get a propane setup, and just just the acetylene for when I just need a small flame. I have a 00 tip for it with a 25mm flame.

Thank you all for your input. I'll let you know how it turns out.


JasonB16/07/2013 07:38:27
22555 forum posts
2634 photos
1 articles

The foil that Keith mentions is Silver solder foil, a thin sheet of solder that is placed in the fluxed joint. Part way down this page.

What part of teh world are you in as that may help us point you in the right direction for supplies, I would avoid the jewellery solders.


Nicholas Farr16/07/2013 09:03:03
3310 forum posts
1524 photos
Posted by Bill Brehm on 15/07/2013 20:57:44:

Wow, I didn't even think my post would be up until later today. So much information I had to take notes as I read. I hope I have address everyone. I'll just paste my notes.


I didn't know about the copper/acetylene problem. I'll look into that. To be honest, I'm not really sure if I can legally have acetylene in my basement. So switching to propane might be required anyway.


Thank you all for your input. I'll let you know how it turns out.



Hi Bill, I don't know about the legal side of things but, your insurance may well be void in the event of a fire or explosion. Please don't think that you will be any safer with Propane as it is assosiated as being a fire and explosion hazard, it is heavier than air and will collect in low lying areas. Your insurance company may well have a dimmer view of Propane than they would of Acetylene. Your insurance company may not cover you at all with any such welding equipment in your basement, so in the event of a fire or explosion you will probaly be on your own for liability.

Acetylene and copper is certainally not a good combination. As said it forms explosive copper acetylides over time and will become unpredictable. Copper acetylides can explode with the slightest of knocks, it does not need any flame or heat to do so. You may ask why the nozzles on your welding tourch are made of copper then, well by the time Acetylene reaches the nozzle it is a mixture and does not pose the threat of forming copper acetylides.

Regards Nick.

Edited By Nicholas Farr on 16/07/2013 09:06:23

Ian S C16/07/2013 11:33:45
7468 forum posts
230 photos

Thanks Nick, thought it was something like that, and if my reference book on the subject was in a warmer part of the house(if I wasn't so lazy), I could have looked it up, I think its listed in the same area as not oiling oxygen valves etc. Ian S C

jason udall16/07/2013 14:46:24
2031 forum posts
41 photos

btw silver acetylide doesn't even need the knock...light will set it off...very exothermic..I guess thats why we don't use silver for the tanks/pipework etc.




Edited By jason udall on 16/07/2013 14:47:40

Bill Brehm16/07/2013 20:17:46
5 forum posts

I'm in the U.S.. Columbus, Ohio. I checked with my local welding supplier about the solder used in air conditioning and refrigeration. He showed me a solder with a 56% silver content. That's about the same as I'm using now.. It was 37.00 GBP (I don't know what the symble for Pound is) for (5 )1/16" x 18" sticks. What I'm using now is about 16.50 GBP for a Troy oz. (don't know the significants of a troy oz, but that is how it's priced) Unfortunately, it's difficult to make a comparision.

He asked what I was doing, and wondered why did I need to use "silver". Good question, I really don't know myself. I told him I needed a high temp solder so that when I add parts prior joints won't re-melt. He then shows me this. Which is a whole lot cheaper.

So, why do we use silver solder?


Well, I got my frame together. Putting the small thin pieces of solder between the parts worked. I still wasn't able to get additional solder to flow down into the joint, but there where no through gaps so I'm satisfied with it. The flux also dried out before I could finish it all. I let it cool, then added more flux and finished. Don't know it that was correct or not, but I'm thankfully done with it.

In the future I'll avoid this kind of technique. To do a good job of it requires more skill than I have at the moment. Cost wise, it's probably better to just get what you need.

I looked into the Acetylene/Copper problem. I haven't used any copper yet, and from what I've read the brass I'm using doen't have enough copper to be a problem. I'm going to look into it more.

Thank you again for all your help. This is a great site, and I continue to get good solutions, and ideas from it. If I ever have anything to contribute, I will certianly do so.


PS I need to make a tubing bender, so I'll be combing over the Tool threads tomorrow. face 1

Edited By Bill Brehm on 16/07/2013 20:18:54

Edited By Bill Brehm on 16/07/2013 20:20:15

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