Incandescent filaments require a complex production process. It begins with a powder metallurgy process where the metal powders are prepared by pressing the powder into low density ingots. The ingots are made more dense by a process called, "sintering." The pressed powder ingot is heated without melting to become a coherent mass. The final density is obtained mechanically in forming the final wire product.

The first step in filament manufacture is using chemical analysis to detect impurities in the raw material. If the chemical requirements are met, the raw material is filter dried and sieved. The ammonium paratungstate is converted to a blue oxide. Controlled amounts of impurities are added to the blue oxide to increase the rigidity of the lamp filament. The blue oxide is then reduced to tungsten metal powder by heating it in a hydrogen atmosphere. The metal powder is then placed in a mold and 20 tons per square inch of hydraulic pressure is applied. This produces a bar about one inch square by 24 inches long. The bar is very brittle and must be handled carefully until it has been baked in a furnace with a hydrogen atmosphere. After baking, the bar is placed in a cylindrical "treating bottle" where pure hydrogen gas and a current of 5,000 to 6,000 amperes is passed through it fusing the tungsten particles. This process shrinks the bar, increases its strength, and causes it's metallic appearance.

The next step is preheating the bar in a hydrogen atmosphere in an electric furnace for swaging or hammering of the tungsten bar. Swaging changes the bar into a rod, gradually diminishing it's diameter and increasing it's length. The diameter is further reduced to the desired diameter in a die-drawing process.

The smallest filament wire currently produced is the one used for the 3 watt 120-volt lamp. It's diameter is approximately 0.3 mils or about 1/10 the diameter of a human hair. In commercial production, specifications require that this diameter be within plus or minus one per cent or about 3/1,000,000 of an inch.

Approved wire is then ready to be wound into spring-like coils. Commonly the tungsten wire is wound on a mandrel or core wire of steel or molybdenum. Some filament coils are wound with 2,065 turns per inch. This means the turns are spaced slightly less than 1/2,000 inch apart. Since none of these turns must touch, machinery of the utmost precision is required. After winding, the wire and its mandrel are cut into specific lengths, depending on the type of lamp the coil is to be used in.

In the next operation, acid is used to dissolve out the mandrel wire. The coils are then baked in hydrogen and visually inspected. Only then are they ready to become part of a lamp.