I'm working on 6-8 frames at the moment, 3 of which are complex sculptures like the God Being Killed frame. I thought I'd go through the process.
The first is for a painting called The Bully that features an exploding volcano. The frame was incorporated into the painting design and would look like rocks being blasted away by the volcano.
The frame will begin with a wooden base, L shaped bits cut and glued. That will hold the picture. Then I designed the rock shapes on paper, my first frame featuring a drawn plan...
I traced those shapes and marked them on 3mm MDF, then used a jigsaw to cut them out. Then I glued 21mm square lengths of wood to the edge of the frame, that will make it strong enough to hold the plaster I'll be coating it with.
Here is the pine frame so far, with the cutouts lying on top...
You can see how the painting would fit inside, slotted in from below. Those cutouts will be stuck underneath/to the back. I left some space at the sides in the middle so that I can attach mirror plates for hanging.
The design also has parts that lean into the picture, showing through the cracks painted elements. The painting is complete, so I put that in the frame and made sure the design fitted with the painted parts. It didn't quite, so I changed and adjusted and when happy cut out those inner pieces too. These will be held from above by second flat parts, like a sandwich. Here is one inner corner glueing.
That will tuck into the inside of the frame.
The next step is to glue the lot together then screw and staple it to make it really strong for the step after that, application of plaster...
Of the other frames, one will include a curtain and a second painting incorporated into the frame. One will include a stained glass window. One will be burned to cinders, one distressed like old oak or ash bark and one stained I think... I did start with a porcelain effect with that but it failed, then considered Hessian then pink puffed silk! But after that I might just stain it turquoise. The frame should complement the artwork and show it in its best light, and there are engineering elements to consider too, but it can easily be more than mere decoration and become part of the artwork itself.