I wanted to try out fractals, not 3D fractals just flames. There is a great free flame editor that anybody can use called Apophysis. It is only available for Windows though, so Mac users are out of luck. The renders took several hours when I rendered an flame 13,000 pixels across, but if you do something reasonably sized then it would be much faster. You do want to have it larger than what you want your final image to be sized, that way you have room to scale or just use parts of the flame or multiple flames.
The image above is a flame I created in Apophysis. They naturally have transparent background and are semi transparent throughout. This allows you to do interesting things with backgrounds and layering.
This image is the same flame but with a white background. They show up much better on dark backgrounds.
The image above is the flame from before except it has been layered several times and given a dark background. I didn’t directly layer it on top of itself, I rotated it and mirrored it so that it is hard to see where there are duplicated elements. Since the flame I used was huge, it was just over 70 mb for the single transparent layer. I can make this desktop background for whatever screen resolution I need. And no, these images are not that size otherwise it would take an eternity to load.