The Fifth String
Sweeney has been credited with adding the fifth string to the fretless banjo, but modern scholarship disputes this anecdotal tradition. The short drone or chanterelle has been with both the banjo and its antecedents from the very beginning. It is equally unlikely that Sweeney added the fourth bass string.
Whether Sweeney set the trend or was simply following it, we can see that after he popularized it on his banjos in the mid to late 1840s, the fifth string was a de facto standard. His other influence was the wooden shell in lieu of a gourd body. After Sweeney, almost all minstrel banjos are made with a wooden shell.
Tension Rods & Wire Strings
In the latter 19th Century there were several adaptations made to the banjo’s form. Tension rods became the most common improvement. Though tack head banjos persisted even into the steel string era, wooden shell banjo heads made the application of this drum technology a simple matter.
After 1878, mechanized wire machines came to America and for the first time made steel strings easily and economically available. Coincidentally at this same time, mechanized gut polishing machines became popular and the quality of gut went down. Unlike precision hand polishing, the early mechanical polishing machines could not auto center on the diameter of the strings like they can today. This caused them to polish off highs and lows in an absolute manner that often weakened the strings and caused them to break. By the turn of the century, steel strings were the new emerging preference. They were louder, cheaper and more durable.
With the advent of steel strings, mechanical tuners were almost a necessity and became a common sight on banjos. Mechanical tuners were available on guitars from the 1820s, but with the exception of Ashborn's banjos in the late 50's, did not really catch on until after the civil war. In most cases, early banjos were not made by skilled luthiers, but rather plantation made by slave wood workers and later by drum makers and turners (carpenters). Geared tuners and frets are not part of their skill set or among their usual tools of the trade. It was not until after the 1870s, that the fretless banjo became less and less common and frets became the new standard.
The 4 string Tenor Banjo was the next evolution of the instrument. The twentieth century ushers in the hybridization of the banjo with other string instruments such as the ukulele and the guitar. Banjo guitars and banjo mandolins still persist, but never became as widely accepted as the traditional banjo.
One of my favorite early 20th Century innovations was the Banjo Light and Heater. Light sockets were clamped into the head with bulbs behind the skin. The warmth of the bulbs kept the skin tight and had the bonus effect of making it glow in the dark!
The "Banjo Light" ad is copied from "Frets" Magazine, October, 1925