I started off with a brown wash (the color was actually "Espresso", so a light coffee-color) of thinned acrylic. This toned down the black and gave an all-over brownish patina look to the cauldron. Then I put brown, red, orange, and black acrylic on a small plate and dabbed my brush into it, before stabbing it randomly over the cauldron. This gave me a mottled appearance as the colors blended into different shades and hues.
When that was dry, I went over it with a mix of red/orange/black which created a dark red-brown color; thinned down, it made a great wash. The colors on the cauldron blended together a bit more and the whole cauldron looked like a single piece of battered, rusted metal.
|Not the best shot, as the colors are too dark.|
|Better- you can see the blending.|
|The other side|
EDIT: Took a look at it in sunlight- it's fine. Looks like an old, beat, rusted, fire-baked cauldron.
|The layers of rust really show here|
|Not as much red on this side, but it still looks like it's been burned in a fire.|