The First Time I ever noticed this unique finishing was on the Jean Baptiste Viot Chronomètre à Paris

Source: Hodinkee
"Charbonnage" is a traditional Parisian watchmaking finishing technique that involves using a block of charcoal and oil (or sometimes 9-micron sandpaper for a similar effect) to gently scrape the surface of (typically in German Silver, sometimes brass also) the main plate or bridges.
A watchmaker manually cuts a point on a block of jeweler's charcoal and applies it to the metal surface using small, controlled circular or undulating movements.
This gentle abrasion creates a unique, soft, and slightly irregular cloud-like or "meteor-like" matte texture that reflects light in a subtle, harmoniously diffused way.
After the texture is achieved, a galvanic treatment may be applied to fix the texture on the surface of the metal.
These beautiful clouds on German Silver captured my imagination. Reminded me of the Automaton in Martin Scorsese's film Hugo and that Era

Source: Hubpages
The Spiritual Successor of Jean Baptiste Viot's technique of Charbonnage is Theo Auffret who has created exceptional pieces
The Petermann Bédat X Auffret Paris Chronomètre d'Observatoire Ref: 1342

Source: Revolution
The Tourbillon à Paris

Source: Hodinkee
Giverny “Blue Train"

Source: sfwatchlover
If someone were to think this is my favorite finishing on a watch, they wouldn't be wrong.
Thank You for Reading 😊🙏