GIMP Fade Dynamic: Simulate Running Out of Ink

In digital calligraphy, achieving the organic imperfection of traditional media requires replicating physical constraints, such as ink depletion. In GIMP, the Fade Dynamic accomplishes this by tying brush characteristics like opacity and size to the length of a stroke. This guide explains the mechanics behind GIMP's Fade Dynamic and how it accurately simulates a traditional dip pen running out of ink.

The Physics of Traditional Ink Depletion

When writing with a traditional dip pen or fountain pen, a finite reservoir of ink clings to the metal nib. As the pen touches the paper and moves:

  1. Initial Flow: The stroke begins saturated, dark, and wide due to maximum liquid volume.
  2. Capillary Draw: As the ink is drawn onto the paper fibers, the reservoir empties.
  3. Dry Stroke: As ink volume drops, surface tension reduces, making the line narrower and faint, eventually terminating in a dry, scratchy stroke.

How GIMP's Fade Dynamic Works

The Fade dynamic in GIMP measures the physical distance traveled by a stroke from the moment the cursor or stylus touches the canvas. Instead of responding to user input variations like pen pressure or velocity, Fade functions strictly as a distance counter.

When mapped to specific brush properties via the Paint Dynamics Matrix, the Fade dynamic progressively reduces brush values from 100% down to 0% over a specified stroke length.

Simulating Ink Depletion in GIMP

To replicate ink depletion, Fade is mapped to two primary brush attributes:

1. Opacity (Ink Transparency)

Mapping Fade to Opacity is the core component of the drying effect. As the stroke extends, GIMP reduces the brush opacity along a linear gradient. The mark transitions from an opaque, wet black or sepia to a translucent grey, mirroring the paper showing through an increasingly thin film of ink.

2. Size (Nib Contact and Liquid Volume)

Mapping Fade to Size mimics the loss of fluid spread. Wet ink slightly bleeds and maintains full contact across the tines of the nib. As ink dries, only the fine tip leaves a mark. Enabling Fade on Size causes the stroke to naturally taper down in width as it runs out of ink.

Key Configuration Settings

To fine-tune the simulation, adjust the following parameters in the Tool Options and Paint Dynamics Editor:

  • Fade Length: Located in the Tool Options under Dynamic Options. This slider sets the precise stroke length (in pixels, millimeters, or inches) required to completely exhaust the ink. A shorter length simulates a dry, scratchy nib, while a longer length simulates a fully loaded reservoir.
  • Repeat Option (None): Set the repeat dropdown to None. This ensures that once the stroke reaches the end of the fade distance, no more ink is laid down until the stylus is lifted and placed down again, effectively "re-dipping" the virtual pen.
  • Fade Curve Adjustment: In the Dynamics Editor, you can customize the falloff curve. A non-linear curve—where the ink remains solid for the first 60% of the stroke and drops off sharply in the final 40%—creates a more natural dip-pen behavior than a strictly linear decline.