Magnesia Blocks Myth Debunked

During a recent conversation with a colleague, I came under some good-natured fire for one of my studio habits: I singe my buffs. Why, you ask? I can offer any number of reasons, but the most honest answer is simply that it’s how I learned to prepare a muslin buff, so it’s the method I continue to use.

But the teasing gave me pause; how do I really know that this is a good approach? Am I trusting habit, tradition, or superstition? And that led me to a broader question: How many of us rely on habit, tradition, or superstition at the bench?

I suspected that the answer to this question is many, so I conducted an informal e-mail survey of the bench jewelers, designers, and educators that I know. The results indicate that there may be as many firmly held beliefs and practices as there are folks who sit at the bench. While I can’t prove or disprove the effectiveness of always patting your dog before leaving for the shop, or soldering with your tongue at the corner of your mouth, I can take a look at bench preparation and practices with an analytical eye.

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The first of these myth challenges follows.


Magnesia Blocks are superior soldering surfaces to Charcoal Blocks

A topic that seems to raise a fair amount of spirited discussion and strong opinions is what is the best soldering surface: firebrick, charcoal, magnesia, solderite-the list goes on. Charcoal is a very traditional choice, but it is seen as having limitations in terms of both longevity and safety. I was curious to see if any of the practices out there served to really mitigate these issues, and how charcoal compares to magnesia, another popular choice.

One common practice to extend the lifespan of a non-compressed charcoal block is to wrap it with a length of binding wire to keep it from splitting apart when heated. Also, Jurgen Maerz of Platinum Guild International told me that he employs an annealing step to help stabilize the block after binding it.

I started my exploration with three unused blocks: two non-compressed charcoal blocks and one magnesia block. I left one charcoal block and the magnesia block completely unaltered, and I wrapped one charcoal block in binding wire and gently heated it with a large reducing flame for about a minute. I then used all three to anneal a small piece of gold and observed the results. It was not a surprise when the magnesia block remained unchanged except for the typical discoloration on the surface, and the unaltered charcoal block split quite dramatically from one edge to the other. What did surprise me was that the charcoal block that was bound and annealed stayed completely stable, and I didn’t hear the crackling that so often accompanies the first few uses of a charcoal block.

I then used both charcoal blocks for the same soldering operation to see if there was any discernable difference, and found that they performed similarly. The only slight difference was the amount of ash and smoldering: the annealed block showed a bit less surface degradation. This led me to conclude that this simple annealing step may, in fact, improve the life span of a charcoal block. I am not comfortable concluding that it makes the use of charcoal any safer by minimizing smoldering, as subsequent soldering operations will break down the surface, and sparking and smoldering will still be an issue. Still, it is a point scored for tradition!

An examination of my soldering bench, however, does take a bit of the glory out of charcoal’s victory here. Like many other goldsmiths, I am a bit frugal, and therefore tend to keep my soldering media until it is utterly unusable for any conceivable purpose. And the reality is that my collection of charcoal block fragments eclipses the magnesia block leftovers even though I use magnesia blocks more regularly than charcoal. Magnesia does not tend to fracture or fall apart given its fibrous composition, and responds nicely to repeated resurfacing. Charcoal simply can’t compete. But charcoal provides a reducing atmosphere and reflects heat in a way that is extremely beneficial when working in sterling silver and for operations such as fusing and fabricating large cabochon bezels.

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Magnesia blocks do not offer these benefits. For my purposes, both will continue to see regular use in my studio, but I have high hopes that this newly acquired trick will allow me to use charcoal more economically in the future.

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