Bakelite resins

In 1907 American-Belgian chemist Leo Baekeland discovered what became Bakelite while searching for a replacement for shellac. This was one of the first of the "plastics" to be developed. Though Bakelite was more commonly used as a molding compound mixed with sawdust and other fillers it also made for a good varnish replacement though this never became as commercially successful as the molded products.
The Bakelite Industry points to the accidental nature of many discoveries and inventions. Playdough and Post it notes are other examples of failed experiments that became successes in unrelated products. Also Teflon here.