Tenifer is not a finish. Tenifer is a Heat Treat process that hardens the outer surface of steel to the point that a file will not scratch it. Glocks made before about 2004 had a dull black slide finish.
This appears to be a Black Oxide finish and it is easily removed with holster wear. These are great canadates to have refinished with our Black Diamond or Satin Hard Chrome.
Newer Glocks that have a shiny black appearance, this is a much superior finish. This finish does not appear to wear off with holster usage. If undamaged I would not recomend replacing it with our Black Diamond Finish

Our Satin Hard Chrome goes over the top of Tenifer without removing it. Chrome is a very hard, dense material, applied over Tenifer makes it even more durable. We have been using this process for nearly 12 years and I have yet to have one come back because it did not hold up.

Recently an Officer that duty carries reported that there is no wear on his Glock that he had refinished in 1995.