One of the chief difficulties was to make the carbon filaments.  Some of the pioneers, such as Sawyer and Mann, attempted to cut these from a piece of carbon.  However, Edison and also Swan turned their attention to forming them by carbonizing a fiber of organic matter.  Filaments cut from paper and threads of cotton and silk were carbonized for this purpose.  Edison scoured the earth for better materials.  He tried a fibrous grass from South America and various kinds of bamboo from other parts of the world.  Thin filaments of split bamboo eventually proved the best material up to that time.  He made many lamps containing filaments of this material, and even until 1910 bamboo was used to some extent in certain lamps.

Of these early days, Edison said: 

It occurred to me that perhaps a filament of carbon could be made to stand in sealed glass vessels, or bulbs, which we were using, exhausted to a high vacuum.  Separate lamps were made in this way independent of the air-pump, and, in October, 1879, we made lamps of paper carbon, and with carbons of common sewing thread, placed in a receiver or bulb made entirely of glass, with the leading-in wires sealed in by fusion.  The whole thing was exhausted by the Sprengel pump to nearly one-millionth of an atmosphere.  The filaments of carbon, although naturally quite fragile owing to their length and small mass, had a smaller radiating surface and higher resistance than we had dared hope.  We had virtually reached the position and condition where the carbons were stable.  In other words, the incandescent lamp as we still know it to-day [1904], in essentially all its particulars unchanged, had been born.

After Edison’s later success with bamboo, Swan invented a process of squirting filaments of nitrocellulose into a coagulating liquid, after which they are carbonized.  Very fine uniform filaments can be made by this process and although improvements have been made from time to time, this method has been employed ever since its invention.  In these later years cotton is dissolved in a suitable solvent such as a solution of zinc chloride and this material is forced through a small diamond die.  This thread when hardened appears similar to cat-gut.  It is cut into proper lengths and bent upon a form.  It is then immersed in plumbago and heated to a high temperature in order to destroy the organic matter.  A carbon filament is the result.  From this point to the finished lamp many operations are performed, but a discussion of these would lead far afield.  The production of a high vacuum is one of the most important processes and manufacturers of incandescent lamps have mastered the art perhaps more thoroughly than any other manufacturers.  At least, their experience in this field made it possible for them to produce quickly and on a large scale such devices as X-ray tubes during the recent war.