I've had really good luck with creating layers set to color burn and using really light pastels as my burn color...thats a great way to make stains.

For example...very light pink set to color burn will create bloodstains. Very light tan will create like coffee stains or such...you can always take whatever shape your stain is and set it to color burn, if its not a light pastel color it will probably appear black, then run image->adjustments->Hue/Saturation and lighten it up and desaturate it a bit til you get a really good stained look. I've not tried this on a parchment background but it works wonders on stone backgrounds...color burn to me is synonymous with dried stain.