Thursday, 2 January 2020


Flux is a material that provides a “wetting” action between the metal (lead or copper in our case) and the solder.

There are various types of flux. Some are of more use in some circumstances than others. Among them are:


This normally comes in a candle-like stick. It is made from rendered animal fat. Although this may put some vegetarians off, it is one of the best fluxes for leaded glass work and will work for copper foil, but is not generally preferred.  It is relatively natural, does not contain chemicals, and does not require re-application if left for a while. Over generous application does not produce any problems during the soldering. It just leaves more solidified tallow to clean after soldering. The cleaning normally requires a mild abrasive such as a brass or fibreglass brush to get the cooled tallow off the piece.


Oleic acid and other safety fluxes

Many of the safety fluxes are made of oleic acid (sometimes called stearin oil). These fluxes do not produce chemical fumes in the soldering process. They are easy to clean up with detergents and warm water. Safety fluxes require re-application if left to dry, as they are only effective while wet. Putting too much on leads to boiling off the liquid, making holes in the solder joint or line.

An example only.  There are many water soluble paste fluxes available

Chemical Paste fluxes

These fluxes come in a variety of compositions. You need to be careful about choosing, as some are very difficult to clean off the glass or solder line or joint. They do produce chemical fumes, so a fume mask is advisable while using this kind of flux. The paste does not require re-application if left, so the whole piece can be fluxed at once.

Acid fluxes

Acid fluxes such as the kind that is in the core of plumbers solder are intended to clean the joint at the same time as acting as the wetting agent. These are not recommended for stained glass work as they can affect the glass surfaces, especially irridised glass. They do produce fumes that require the user to have on a fume mask while soldering. The ease of cleaning relates to the particular composition of the flux, so testing samples is required before application.

See also:
Flux, an introduction
Fluxes, a description
The Purpose of flux
The action of fluxes
Soldering fluxes

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