During a filament change, a small amount of melted plastic remains in the nozzle. As the new filament is loaded, it’s melted as well and starts pushing the nozzle content out. During this time, you’ll see a gradual change in the color of the extruded filament.
In order to ensure a sharp color transition, PrusaSlicer provides several ways to deposit this filament:
The amount of material to be purged during a filament change can be set by clicking on the Purging volumes… button in the right toolbar.
The sheep on the right has the white color contaminated by the blue pigment from the previous filament
By default, you can simply set how much material will be purged when the filament is being unloaded or loaded. This lets you optimize the amount of wasted filament by, for example, decreasing the amount to purge when loading black filament. On the other hand, you can increase the value when transitioning to very light colors, to ensure they are not contaminated by previous colors.
Transition Black to White = Black unload + White load = 80 + 70 = 150 mm³
Transition White to Black = White unload + Black load = 20 + 30 = 50 mm³
In the advanced mode, you'll be presented with a matrix. Each cell represents the amount of filament required to purge during filament change from filament X (left column) to filament Y (top row).