I weathered one side heavier than the other, and pretty much just followed their directions, and I wasn't working from any photographs. Mostly this is to understand their process, and use it as a foundation for other approaches.
Overall I'm pretty happy with the first attempt. Because these are acrylic washes, there's a bit of the rounded edges in a few places since the color pools there. So I'll want to address that.
I also added some Pan Pastels afterwards to see how that would alter the weathering: