Heat Shield vs. Heat Sink: or Where Do I Put the Tweezers?!

Lowther.Heat-Shield-VS-Heat-SinkYou’ve put a bunch of time into a piece, and now you have to solder a ring onto the end of a chain, or an ear post onto the back of an earring, and you REALLY don’t want to ruin all your hard work on this last delicate step by melting or annealing something that wasn’t supposed to be melted or annealed! How do you protect your tender bits from the relentless flame?!

The root problem? Sterling silver transfers heat the way a fire hose transfers water.  Focus the flame of your torch on one end of a silver wire, and the heat will whip down to the other end and burn you before “ouch!” makes it from brain to lip. Copper is like this too.  Gold is almost the opposite, but that’s a topic for another post.

You’re unlikely to have been fondling your silver or copper while heating it, but you’ve probably run into this issue and done a spot of swearing when you couldn’t get solder to flow on a big piece of metal.  This curse-worthy sticky wicket is the by-product of the “heat hose” characteristic (high thermal conductivity, in engineering terms), because you have to get the WHOLE piece of silver or copper up to the flow temperature of your solder before the solder will actually go ahead and flow!

As you heat one part of the piece, heat is being wicked away by the parts your flame isn’t touching.  In the case of our chain, this means that long before that end ring is hot enough to solder closed, the rings touching it will have been heated more than enough to anneal them, making them soft and prone to be pulled out of shape.

What to do?

Use Tweezers as a heat SHIELD:

Focus the flame on the end ring.
Focus the flame on the end ring.

The trick here is to use the metal of the cross-lock tweezers as a heat shield, protecting the rings lower down in the chain by siphoning excess heat out of the end ring and into the steel tweezers.

Grip the work just BELOW the part to be soldered.  You want the part in question to stand proud of the tweezers, alone and undefended from the flame! This way it will quickly heat up to soldering temperature, and you’ll be finished with your task long before anything else gets too hot.

Note unmelted flux on lower rings.

Note unmelted flux on lower rings.

Notice that the flux on the top ring is glassy from being melted, while the flux on most of the area below the tweezers is still crusty white, meaning it never even got hot enough to melt! Even the rings immediately below the tweezers still have some bumpy texture in the flux, so they did not get hot enough to anneal the metal.  Meanwhile, the top ring was plenty hot enough for the solder to flow without issue (Generally it’s a good idea to use ‘easy’ solder for such an operation – no need to push the envelope if you don’t have to.)

Meanwhile, here’s what NOT to do:

Just soldering the end ring? DON'T do it this way!

Just soldering the end ring? DON’T do it this way!

You DON’T want to use the tweezers this way if you JUST want to solder the end ring.

With the end ring gripped in the tweezers, you have to pump a tremendous amount of heat into that part in order to get it hot enough for any solder touching it to flow – enough heat, in fact, to make the tweezers glow red and to anneal a considerable number of the rings in the chain below (any link with fully melted flux on it is annealed…)

You only want this configuration if the goal is to attach something tiny to a larger piece.

Which is when you want to…

Use Tweezers as a heat SINK:

Tweezers act as a heat sink and protect fragile ear post.

Tweezers act as a heat sink to protect a delicate part.

Here the metal of the cross-lock tweezers acts as a heat sink, protecting the wee part by sucking heat out of it as fast as the flame pushes it in.  If a very small piece of metal sticks out and is unprotected from the heat while you are trying to get the whole big piece hot enough for solder to flow, chances are the small piece will melt before the solder does. 

Grip the tiny, vulnerable part with the cross-lock tweezers, and then focus on heating the LARGE piece of metal involved in this operation.  Very likely you won’t need to play the torch on the wee bit at all, as it will hoover up plenty of heat from its contact point. If you do need to heat it a bit, heat the tweezers, and heat will flow back into the ear post.

You need to steady your hand to do this, because if your hand shakes and moves the ear post just at the moment that the solder flows, and before the solder “freezes”, your solder joint will separate.  To forestall yet more swearing, figure out a position that will allow you to support your hand BEFORE you turn on your torch.

Steady your hand so that no weight is applied to the ear post.

Steady your hand so that no weight is applied to the ear post.

See my ring finger lying on the solder brick?  And my little finger pressing into the side of the brick? Rock solid support.  Very little weight on the ear post.  The ear post is so small and thin that if you apply much pressure to it when it’s hot it may collapse and break.

You might think you could avoid this trouble by gripping the post at the base, but that’s NOT a good idea.

DON'T do this! Or you'll probably melt your ear post.

DON’T do this! Or you’ll probably melt your ear post.

This configuration is dangerous because it leaves the tip of the ear post exposed to the ravages of the heat from the torch.  The fact that the tweezers are lying on the larger piece of metal will only make the situation WORSE because they will suck heat from the big part, so that it takes even longer to reach the proper temperature.  Meanwhile, your ear post may have become a uselessly “decorative” melted ball…

But that won’t happen to you, because now you know where to put the tweezers :)!

Signature - Lowther

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12 Responses to Heat Shield vs. Heat Sink: or Where Do I Put the Tweezers?!

  1. Marguerite Band says:

    Many thanks for this information Julia. Your explanation is so clear that I won’t need to be so nervous next time.
    Marguerite Band

  2. Joanne Forman says:

    Thanks Julia. Your explanation of heat sinks and placement of tweezers to the best advantage when soldering is excellent. I’m thinking in a very different way when I approach a solder project thanks to your clear and methodical explanations. I can now think through and approach soldering an opened ring on a pair of post and ball earrings. You’ve opened doors for me ! Thanks again.

  3. Lecia Woessner says:

    I wound up here somehow & I’m so glad that I did! What a wealth of information! Thank you so much! I am constantly searching the web trying to find soldering/metalsmithing information because I am self-taught & really don’t know what the hell I’m doing & this type of info is invaluable to me! I’ll be back!

  4. Kat Mac says:

    Great topic and tutorial.. Thanks

  5. Wendy says:

    This is THE BEST explanation I’ve found about heat sink and heat shield. I too am self taught like Lecia above, and this is a fantastic post. Thanks so much!

  6. Maria Nunez says:

    Thank you so much, Julia. Very helpful info since I just bought ear posts and was wondering what was the best way to solder it.
    Thanks again 🙂

  7. petaluna says:

    Great article! Would the ear post in this scenario be annealed as it is soldered to the earring? How do you harden it after if so? I haven’t done post style yet, but i find when I twist my soldered ear wires, they usually break before they get stiff enough (using 20 gauge).

    • julialowther says:

      Yes, the ear post is generally annealed as it is soldered on. I twist mine after soldering to harden them, using a pair of parallel jaw pliers to grab the post. After I give the post a couple of twists, I usually grab the base of the post with the tips of a pair of chain-nose pliers, and holding that spot steady, twist a bit more with the parallel jaw pliers. If the post breaks off before it hardens, it wasn’t properly soldered on in the first place.

      To harden longer ear wires, I planish them a bit to work harden them. If you want to twist a longer wire enough to harden it, then you will definitely have to grip it tightly at the base to keep it from twisting off right where it joins the piece.

  8. lynne says:

    Great explanation, Thank you! ….this is so very helpful to a newbie like me.

  9. Bear Hopkins says:

    fantastic! thank you for this!!

  10. Paula says:

    Thanks Julia for the well written instructions.

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