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a tribute and my humble
contribution of brushes,
scripts and tips for the GNU
Image Manipulation Program

Script-Fu -> Watercolor

This is a script with a single adjustment which lends a soft, watercolor effect to an image. Latest version also allows changes to be left on a separate layer (if you choose not to "flatten", so the results can be "toned-down" as needed. (See lower example)

Watercolor Dialog

Original Image

Detail from "the Lovers" by Pablo Picasso

result:

Default Settings

layer dialog:

to adjust results of watercolor script

Since watercolor can create a new layer and leave it -- you can adjust the layer opacity to tone the effect down as needed. You can choose from the image menu:
WINDOWS > DOCKABLE DIALOGS > LAYERS
(or Ctrl + L)
There you can set the layer opacity. In the example I drag the slider to 50% . . . the "Watercolor" layer was already selected.

Download

210_artist_water-paint-effect.scm

;  This script should be placed 
;  in the user or system-wide script folder.
;
;  Windows Vista/7/8/10)
;  C:\Program Files\GIMP 2\share\gimp\2.0\scripts
;  or
;  C:\Users\YOUR-NAME\.gimp-2.8\scripts
; 
;  Windows XP
;  C:\Program Files\GIMP 2\share\gimp\2.0\scripts
;  or
;  C:\Documents and Settings\yourname\.gimp-2.8\scripts   
; 
;  Linux
;  /home/yourname/.gimp-2.8/scripts  
; 
;  Linux system-wide
;  /usr/share/gimp/2.0/scripts
;