Chemically, is there a difference between the Jax Brown-Black and the Jax Black? It seems to me that the Brown-Black is a diluted version of the Black.

The Jax Brown-Black and the Jax Black are actually quite different, chemically and in appearance. The Jax Brown-Black is water-clear (or close to it) and the Jax Black is a blue-based solution. The Jax Black will produce no brown tones at all — the metal will go right to black. The Brown-Black will start at brown and work its way up to black (almost).