While sitting here doing hand sanding the mind always tends to wander and today I started thinking about how our ancestors went about soldering. Now days we have pre-made flux, soft/medium/hard solder sheets, and oxy propane torch which make the process more or less straight forward. When you take all of that away and have only a forge to heat I suppose you could lay your solder work on a steel plate and slowly heat the plate until enough heat transfers to the piece to were the solder flows, but still leaves the question of flux and solder.

Does anyone know what was used for flux and or how it may have been made?

Also do we know how solder was made, and if they were able to make it with varying melt temperatures to help with some of the complex work that we see?

I suppose I should mention that I am pondering migration era work, however later examples of process and techniques are more then welcome. If we don't know how it was done in the migration era, then perhaps looking at "later" information would help to figure out what could have been done?

I am basing this on modern practices of interpreters I have watched and work I have done myself and travels in the 3rd world. It may be wrong but it is all very straightforward and in all cases is an easy way of doing the work.

soft solder ie lead based solder can use mutton fat/tallow as a flux.

silver solder used borax/sodium borate which is a mined salt I believe

Brass solder/braze or copper alloy based solders also use sodium borate

both silver solders and copper alloy solders were applied as filings or small chips cut from larger pieces that were premade.

For example 100% silver solder will melt at the same temp as solder so to make silver solder you alloy a piece of silver with other elements such as tin, nickle or copper to lower the melting temp and different amounts make for different temp ranges. Alloy the silver draw it out and you have silver solder.

Yes plate heating is a way, as is direct fire heating if appropriate to the piece or if you have various temp ranges of solder, this may be an option. Spirit blow lamps were used in the medieval world and judging by the migration era work and the work that followed I suspect blow lamps were used then as well.

I believe soldering was called 'sweating' in medieval terminology.

Tod

Another use of the term "sweating" is the method used to attach a front sight to a rifle barrel by a band around the muzzle: the band is made slightly too small to fit around the barrel. Then the barrel is chilled so it contracts, and the band is heated until it expands enough to force over the end of the barrel. When the temperatures equalize, the band is on there tight!

Ceramic bunsen burners are known from the bronze age onwards, which create a thin very hot flame. They were ceramic cones with a hole in the top for the flame, and lots of small holes in the side to draw in air.

One method I remember being used in the old days was the use of f.e. copper salts, which when put in a reducing flame will turn back into metal, and solder the parts together.

Leo and Jeoren provide most of the story (though I'm not convinced about the ceramic bunsen burners).

The easiest solder to use is "soft" solder, usually a mixture of tin and lead. It doesn't take high temperatures to use, but it makes repairs very difficult and isn't terribly strong,. This type of solder can fill gaps . It was used by the Romans (see Lag and Hughes, "Joining Techniques", in Aspects of Early Metallurgy), and is described by Biringuccio in the 16th century. I'm not sure what fluxes were used.

The next type is what jewellers call "hard" or "silver" solder. It's what most goldsmiths use today. The jeweller makes an alloy with a lower melting temperature than his work metal, usually by adding silver or copper, or both. The work is then fluxed, with borax, wine lees (Theophilus), natron (Pliny), or simple salt. The solder can be added to the seams now, in the form of small chunks or paillons, or during the heating. The work is brought up to heat, and the solder flows. It will not fill gaps.

The final type is called by quite a few names: colloidal hard soldering, diffusion bonding, eutectic soldering, etc.. Jack Ogden (Jewellery in the Ancient World) believes that it was in use in the Eastern Mediterranian by 2000 BC. The process is described by Theophilus, and Coatsworth and Pinder (The Art of the Anglo-Saxon Goldsmith) think that most soldered Anglo-Saxon jewellery was made with this method. A copper salt is mixed with an organic binder (often a glue, which helps hold small parts in place).
"The resulting liquid or paste is applied to the area of the joint to be soldered, and heated. As the metal heats up, the organic material carbonises, and in return reduces the copper salt to copper, which mixes with the gold to form an alloy with a lower melting point. The capillary effect at the area of contact within the joint pulls this alloy into the joint, and so solders the two parts together."( C+P, page 98)

This method is lots of fun as it it is easy to melt the whole work. Unlike the first two methods, though, almost no solder is visible on the finished piece. This makes it the method of choice if you are working with tiny granules (Etruscan, etc) or fine wires (Anglo-Saxon, etc).

Neither Theophilus nor Birincuccio mention the use of the blowpipe for soldering. Both describe using a small furnace, or a small section of a larger forge (charcoal, not coal). Air for increased O2 and thus higher heat, is introduced in both accounts by mouth or bellows. The only place T has a blowpipe is in the section on glassblowing.

mark

How about a old fashioned soldering iron? The iron type with a pyramidal iron head on a shaft; you heat the tip then touch it to the joint to be soldered.