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If you think this soldering article is for beginners only, think again!

soldering

Given that it's such a basic task, soldering is such a complex procedure! Whether soldering is something you do everyday or you have just picked up your torch for the first time there is far more to soldering than you might think.  Okay, so soldering a seam making a simple join is relatively easy; new jewellers will pick it up very quickly and more experienced metalsmiths won't even think about it.  And that is the crux of this article - if you take a little time to understand what is happening when you solder you be able to, a) understand why things don't always work the way they expect them to and, b) be able to undertake more complicated soldering tasks with greater confidence.

How to Choose Solder

Solder is solder is solder, right?  Wrong!  There is actually no standard temperature range for solders so, when you are choosing between hard, medium, and easy solders, the melting points are relevant to that particular supplier only. Therefore, you must check out the flow temperature with each supplier that you use.  Of course, the basic essential is that the melting point of your solder is lower than the melting point of the metal you are soldering, otherwise all your hard work will be nothing but a molten metal pool on the bench.

Now, here's a good quote for you:

'The goal of soldering should be to produce the strongest bond necessary for the application, with a suitable colour match.' (Greg Todd, MJSA Journal)

The colour aspect is, of course, most relevant to gold solders because different combinations and ratios of alloys produce a whole range of colours.  However, many of us are guilty of turning a blind eye to another important consideration mentioned in that quote, the strongest bond necessary for the application.  The strongest possible bond isn't always the most applicable bond.

If you are working on a piece that is likely to need periodical changes or adjustments, you do not need the strongest bond, in fact, the strongest bond may actually eventually lead to damage of the piece.  Restyling, resizing, and repairing are far more easily carried out when the solder joints are weaker.  As a general rule of thumb, the lower the melting point of the solder, the weaker the bond produced so, with future repairs and replacements in mind, you might think about using easy or medium solder rather than going for the hard stuff!

Forming the Solder Joint

We've all been told that 'solder doesn't fill gaps.'  If you can see anything but the tiniest line of light through the joint you are unlikely to produce a sound joint.  It might look firm, it might even feel firm (unless you rock it a bit, but you won't do that will you!) but this will not be a sound joint.  By spending time getting the joint properly aligned you will:

  1. Lessen the chances of your soldered joint falling apart (which is why you hold back from giving it a bit of a shove!)
  2. Ensure the solder joint is more or less invisible.  All solder joints cause a ridge or a valley, the smaller the gap between the edges, the smaller that ridge or valley.
  3. Eliminate any trapped bubbles of gas, which cause the solder joint to become porous.  This porosity shows as pin-prick holes within the joint.
  4. Reduce the chances of joint shrinkage.  If the joint shrinks, the solder becomes porous, once again leading to those pin-prick holes.

Make Sure your Solder Joint is Clean

At every stage of the soldering process make sure that all your components are clean.

  1. Make sure the piece you are soldering is clean and free from any contaminants whatsoever, this includes grease from your fingertips, so
  2. Clean any abrasive or polish residues from your hands
  3. Use an oxide-preventing product, such as a solution of boric acid and methylated spirits, Magic Boric, Easyflo, or another of the many brands available
  4. Before soldering again, remove any oxidisation that has formed - generally, dropping the piece in the pickle pot will suffice but you may need to use some emery paper or even a file if the oxidisation is severe
  5. Heavily contaminated pickle can cause oxidisation so, if in doubt, mix up a fresh batch

Why you should use Flux when Soldering

Flux has a variety of functions and, unless you are using ready-fluxed solder paste (not the topic of this article) it must be used.

Flux:

  1. reduces surface tension between the solder and the metal
  2. protects the surface of the metal from oxidisation
  3. enhances solder flow.

Because flux enhances solder flow, only apply it to the joint you are soldering, otherwise the solder will flow wherever it can.

The Heat Source

Now, here's a brain melter: the heat source is not, as most people believe, the torch; it is, in fact, the metal you are soldering! This is why:

  1. You should apply heat to the metal and not the solder.  This is one of the most common problems faced by new jewellers; they know their torch is producing plenty of heat but still the solder doesn't flow.  The reason for this is that they are heating the solder and not the metal, if the metal isn't at the right temperature, the solder will not flow into it.
  2. You should have the solder in contact with the metal, which is obvious really when you understand where the heat source is.
  3. You should keep any areas you want free from solder cool. The solder won't flow if into an area that is not hot enough.
  4. You shouldn't overheat the metal.  If you do overheat, you will form an alloy rather than a join.  That is, the solder will fuse with the metal and this will lead to a grainy-textured dip in the finished piece.  Over time this area will also become brittle.  This situation tends to occur when heat is directed at the solder rather than the metal as more and more heat is applied in an attempt to get the solder to flow.
  5. You shouldn't be stingy with your solder!  Especially when using hard solder, by the time it has reached flow-point some solder will have penetrated the metal and, if you haven't used enough, there won't be enough left to make a strong joint.

Article by Jo Walker who is Technical Director for the Guild of Jewellery Designers

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