Much like sewing, not a whole lot has changed in the last few millennia. Soldering has been a technique in use since early on in the process of metalworking. Give or take 5,000 years. And metal, like fabric, can be made into hundreds of thousands of different things, but the methods of making those things are fairly limited, and defined by the material's properties. Metal can melt. Metal can bend. Metal can harden and soften. Metal is reactive to some acids. Metal can be mechanically fastened to other materials. And metal can be melted and "fused" onto other metals or itself (welding), or a metal with a lower melting point can be used like glue to fuse two other pieces of metal. Which is soldering.
By its nature, metal has to be clean and free from oxidation in order for it to be properly soldered. Flux is what we use to prevent oxidation, and there are several different chemical forms of flux, with the simplest being a borax cone that gets combined with distilled water in an unglazed ceramic dish. Borax and its chemical properties with respect to metal were known and can be documented in medieval metalsmithing practices. Interestingly enough, while Theophilus of Edessa mentions the use of borax in "On Divers Arts" (12th century), he separately provides a recipe for flux to be used in soldering silver. It involves the resin left at the bottom of wine bottles. He also provides a recipe for soldering gold, using lye, salt, and copper, but mentions that it can be used to solder both gold and silver. Cellini, in the 16th century, simply indicates borax.
Heat must be used to melt, weld, fuse, or solder metal. Modernly, most people use torches, with working pieces placed upon heat-reflective fire safe surfaces. I, and many people, use a simple charcoal block. There are other options available, including ceramic honeycomb, vermiculite, or magnesia blocks. Now, specifically, I work on a dense charcoal block made specifically for this use, that sits on a vermiculite block, that sits on my desk. The vermiculite block is bigger, and acts as a secondary, heat-safe workspace for things to be set upon safely, and to act as a safety if sparks fly. Charcoal doesn't act as a heat sink. It reflects heat back on your piece, and it can, by its own nature, ignite and smolder, so working with it on a secondary heat-safe surface is important. Some people choose to douse or quench their charcoal blocks after use.
That said, charcoal is indispensible to the discussion about medieval metalwork. Charcoal fires can get as hot as 2110'F. In a forge, with oxygen added to it via bellows, a coal fire can get as hot as 3590'F. Charcoal fires are how medieval metalworking was accomplished. For reference, the melting point of silver is 1,763'F, the melting point of gold is 1,948'F, and the melting point of steel is 2500'F.
Theophilus describes building a forge on a bed of sand with charcoal, and then for a soldering process, placing the pieces to be soldered on the charcoal, supporting them with more coal if needs be, and then building up charcoal walls around the piece, so that it can be heated evenly all the way around. Gaps were left so that the piece could be observed through heating. The coal fire was fed oxygen with bellows until it became hot enough for the solder to flow, and then the charcoal was removed and the piece was taken off the heat.
Ultimately, while a few of the tools have gotten better, and the visual aids and artificial lighting we have modernly make fine detailed work easier, the actual processes of metalworking have been virtually unchanged for millennia, which is pretty danged cool, if you ask me.
No comments:
Post a Comment