An oxy-propane torch burns propane gas in a stream of pure oxygen to produce a hot, focused flame suitable for the routine fabrication, soldering, and annealing operations of a karat-gold and sterling-silver jewellery bench. Maximum neutral-flame temperature is approximately 2,800 degrees Celsius — cooler than oxy-acetylene's 3,100 but more than adequate for any operation short of platinum welding. For most studio and small-production benches, oxy-propane is the dominant working torch.

Configuration

A typical bench setup uses a small portable propane cylinder or a piped supply, a cylinder of compressed oxygen, two regulators stepping cylinder pressure down to working pressure, two hoses (oxygen green or black, propane red or orange by convention), a mixing handle, and a set of interchangeable tips. Working pressures are low — a few kilopascals on each side at the handle — and the flame is shaped by the choice of tip and the oxygen-to-fuel ratio. A neutral flame is the working default; a slightly reducing flame is used where oxidation of the work is a concern, and an oxidising flame is used for specific cutting and melting operations.

Propane is more forgiving than acetylene as a stored fuel. Cylinders can be laid on their side, the gas does not decompose at cylinder pressures, and leaks are easier to detect by smell. The simpler safety profile is one of the reasons oxy-propane has displaced oxy-acetylene in many jewellery workshops over the last several decades, particularly in benches that do not regularly work platinum.

Use at the bench

Oxy-propane handles all routine sterling and karat-gold work: soldering chains and findings, annealing wire and sheet, fabricating bezels and prongs, retipping worn settings, sizing rings up and down, and joining components for general repair. With a large tip the same torch melts casting buttons of up to 100 grams and pre-heats casting flasks. With a small tip and careful setting, the flame is precise enough for the smallest filigree and granulation work.

For high-karat gold (18 to 24 karat) and for some palladium work, oxy-propane provides adequate temperature headroom. For platinum, however, the flame is too cool for clean welding, and platinum benches keep an oxy-acetylene or hydrogen-oxygen torch alongside the oxy-propane for that purpose. Many production shops run two systems on adjacent benches and switch between them according to the metal in hand.

Operating practice

The torch is lit by opening the propane valve at the handle, lighting with a flint striker, and then opening the oxygen valve until the flame is set to a clean blue inner cone. To extinguish, the oxygen is closed first and the propane second, which prevents the loud pop of an air-rich flame at shutdown. The torch is set down only on a tip-up rest, never laid on the bench. Regulators are checked daily before work, and hoses are inspected for kinks, abrasion, and embrittlement on a regular schedule.

Tip selection is the principal variable in routine work. A small tip with a tightly focused flame is used for delicate findings; a medium tip for general bench solder; a large tip for melting and for casting flask preheats. Mixing the tip to the operation rather than overdriving a small tip with high pressures gives the cleanest results and the longest tip life.

In the trade

Oxy-propane is the working compromise between the simplicity of air-propane (handheld plumber-style torches that are too cool for many jewellery operations) and the high heat and added complexity of oxy-acetylene. Its installed base across jewellery workshops, schools, and bench programs reflects the fact that it covers the largest share of routine bench work at acceptable safety and operating cost. The practical limit is platinum: any workshop that handles platinum on a regular basis will run a separate, higher-temperature torch alongside the oxy-propane rig.

Further reading

• GIA — jewellery manufacturing reference
• International Gem Society — bench torches
• GIA Gems & Gemology — fabrication practice