Hey Flux

HEY FLUX!

What is this stuff? Why won't solder stick without it? How come Mike's so good looking? All questions in search of an answer.

Flux is that nasty liquid/creme/paste that's first applied to metal (lead, copper, zinc, brass) prior to soldering. Flux cleans the metal and the soldering iron of corrosion and promotes even heating of the metal. Believe it or not, solder will not flow over the slightest corrosion, and that starts the instant metal comes in contact with this environment of ours. Any corrosion will act as an insulator and prevent the metal under it from heating up. This is especially applicable to lead, as it tends to oxidize quicker than most other metals. While this might worry you, (as if world peace and hunger weren't already enough), once the surface has completely oxidized, it seals the interior, stopping any further corrosion. That's why an old leaded panel can be resoldered if the skin of the lead joint has been scrapped down to the shiny metal underneath (funny, the same process doesn't work on my mother-in-law).

Now that you know that flux is not some pyramid scheme, it is my duty to educate you as to which one to buy. As you'll no doubt discover, as in stained glass shops, not all fluxes are created equal. While they're all acidic, their degree varies. Ideally, you want to use the mildest flux possible for that particular application. It's for this reason different metals require different fluxes.

Lead is traditionally soldered with an organic flux that is both oily and waxy, such as tallow or palm oil. Since the invention of the rotary Wankel engine however, most craftspeople have advanced somewhat and now use oleic acid. Oleic is an oily liquid, very low in acidity, and is applied with a brush. The residue must be wiped off with a rag after soldering to stop the corrosiveness of the oleic from staining the lead. The one drawback of this flux is it's smell- but this can be used to your advantage in some unpleasant social situations.

Copper foil and copper/brass/zinc cames require a more active, and therefore more acidic flux. The corrosive acid, zinc chloride, is the common ingredient to this group. Because zinc chloride is a very watery liquid, it is often found today suspended in various carriers such as glycerin (making it the consistency of syrup) or even thicker, to the point of it spreading like hand creme. The advantage of this is the easier control of its coverage, and to reduce its tendency to boil and evaporate away. The disadvantage of this is these carriers are somewhat difficult to clean off your work. But, that is why chemical companies exist. After screwing up the lives of the people of Love Canal, these chemists turned their attentions towards our industry and came up with special neutralizers that are soapy enough to cut through the residues from these fluxes, and also alkaline enough to aid in chemically neutralizing the flux, stopping it from further corroding the solder.

So there you have it. Just remember, whatever flux you use, make sure you have adequate ventilation. Flux fumes can irritate the skin, eyes and mucous membranes (there's a scary thought). For those with sensitive skin, a silicone based hand creme is a good idea.

Fantasy In Glass