We start off with a sketch

 

 

And on a new layer let’s make the base on a flat surface

 

 

Now lets use the mesh tool transform and add it in place

Duplicate the layer, place it underneath, and change the color to a darker one

 

 

Now repair any edges that dont connect

Use airbrush to add some color variations

 

 

Add background

 

 

And some some sparks

Grab any texture brush you like , and continue adding details

Color balance adjustments

Make new layers and add more details

Polishing time

 

 

More details

Final details and scratches