A little diversion for you when you have the time .. Celtic Knot Diffusions (yes really!)

Starting image:


After 10 iterations of z22's reaction diffusion script (with threshold=127) and Color>Curves adjusted:


With "Incandescent" radial background:

jontait2

In fact you can start with just about any image and get lots of interesting "contours" just using Color>Curves after the diffusion script.

This is an interesting effect:


To do:
File>New (white)
Filters>Render>Pattern>Jigsaw (6 x 3 tiles, bevel width 8)
Filters>Generic>reaction diffusion (10 iterations)
Colors>Curves ..make 5 or 6 peaks and troughs (not too closely spaced otherwise you'll get aliasing)
Colors>Color to alpha (white)
then overlay on a (heavily) bevelled image such as the honeycomb pattern or a BRL logo.

Very interesting topic.
Not only the effect (very interesting) - but how to write a script-fu.

@MareroQ:
If you're interested in writing Script-Fu scripts, start with the Gimp Manual Chapter 13 Section 2:
http://docs.gimp.org/en/gimp-concepts-script-fu.html

I like your box jontait2, it would make a nice gift box or wrapping paper.

Just for you, Molly..