It couldn't be easier.
Make a bead and then roll it, while it's still hot but not drippy, in plain old baking soda.
I have my soda in a small stainless steel dish.
Put the soda coated bead back in the flame and watch it sizzle.
Start way out in the flame - if it gets too hot you may not get good fizzle and the bead might stay sort of shiny. Some colors work better than others, start with turquoise it goes crazy.
Want more pitting? Roll it in the soda again and burn off the soda again.
When you have the perfect, perfect amount of crusty ancient-ness put it in your kiln.
Most of these beads were triple dipped.
Just try it, you'll get the hang of it right away.
Be sure you have good ventilation.
When they come out of the kiln they can be a little too crusty and rough.
Rinse them off in water.
Then brush them with a very stiff brush to knock to off any loose grit and clean out the craters.
Lastly, I give them a light coat of Renaissance wax, let dry and buff.
The light wax coating makes them much nicer to the touch.