First off, let me say that I am certainly not the originator of this idea - I think it's been around forever. But, I've looked all over the place and I can't find any tutorial/instructions/name for this technique, so I am showing you how I did my Nepal piece and calling it Ancient Fragments, which is what I wanted my "exotic" artwork to look like. Okay, let's get started!
The next step is the most important! You need to let your mud dry until it's just the right consistency to stamp into. If it's too wet, you'll end up with an unrecognizable blob, too dry and you won't get an impression at all. Because I have no patience, I use my heat gun to speed up the process. Just keep checking until you think it's ready. *This will take a very short time - don't leave it overnight and expect to be able to stamp into it!
Take a bold image stamp (this one is from Jim Stephen) and press evenly into the mud. Pull up and check your impression. If it looks good, continue to stamp, covering the entire surface. If it's too wet, smooth it with your knife and wait a bit. If it's too dry, you'll either need to add another layer of mud or start over again. You might try re-wetting it, I haven't done that, but it might work.
Let dry - you can use your heat gun to speed this up!
When dry cover the entire surface with slightly watered down acrylic paint. I used burnt umber craft paint.
Wipe/blot off with paper towel. Oooh, how cool does that look now? Your paint will catch in all the little cracks and crevices. I was tempted to stop here!
The next part is entirely up to you and your creative muse! I can't tell you what feels right for what you're trying to achieve, you have to experiment for yourself. For mine, I painted the depressions with red acrylic paint, added Brushed Corduroy Distress ink, more brown paint, gold and copper rub on paint (from RockCandy Studios), oil crayon, and black acrylic paint. You just have to play with it until you're happy! I also sealed mine with an acrylic sealer when I was done.
I hope you've enjoyed this - please let me know if you try it and send a link to your artwork!