(07-07-2021, 05:56 AM)Blighty Wrote: There are two ways.
The first is to use a gih brush. Duplicate the image many times. Rotate each layer a little more than the previous one until there is one complete rotation.
The second method is to use a gbr brush and dynamics.
See here:
http://gimpchat.com/viewtopic.php?f=12&t=18967
Thanks, +1 for the link, some interesting twists and good explanations,
I discovered some unexpected effect like with the triangular wave while I was tinkering

It does work well with a clipboard brush as well

To resume the most important are in the brush options dynamics > fade length and "repeat = sawtooth wave and in the matrix Angle crossed with Fade
again, thanks a lot, much appreciated