Soldering metal together to make jewellery is a basic necessity in jewellery making. Since it's like welding, it may seem daunting at first, but soldering jewellery is done on a much smaller scale. Torches are not just for soldering, they're used to anneal the metal, which is heating it to ensure it's malleable enough to be worked with. Different torches use different types of fuel, such as butane or propane, and each burns at a specific temperature.
That hand-held butane torch that you use to melt the sugar on top of your creme brulee is pretty much the same as butane torches that can be used for making jewellery. Butane torches are often small, hand-held torches that are portable and have a small flame that ignites with the push of a button. These torches do not get very hot and are useful when soldering very fine pieces of jewellery, such as small chains or rings.
Propane torches are hotter than butane torches and use propane as a source of fuel. A plumber's propane torch can be used for making jewellery, however, there are jewellery-specific torches that are easier to use. These torches have interchangeable tips and a regulator that allows you to adjust how much air you want to let into the torch, which mixes with the propane so that it burns hotter or cooler. This torch, often called "The Whale," connects to a hose fitted with an attachment that connects to small propane cylinders that are often used for camping. Propane is a clean-burning fuel that doesn't cause metal to oxidise as readily as acetylene, for example.
An acetylene torch uses a single "B tank" of acetylene that's made from natural gas. It gets hotter than propane, so it's a good alternative when soldering larger pieces of jewellery. The downside: Acetylene is a "dirtier" gas, so it oxidises metal more quickly. The B tank acetylene uses ambient oxygen -- oxygen in the air -- that mixes with the gas to control the heat. There's just one dial; the more you open the gas, the larger and hotter the flame.
The oxyacetylene torch is characterised by two tanks: one with gas and the other with oxygen. This torch is the most expense of the bunch, but it also gets the hottest, so it's one of the preferred choices of professional jewellers. There are three regulators to deal with: one for the torch, one for the gas and one for the oxygen. Once the gas is lit, the oxygen regulator is used to let oxygen into the flame.