I actually tried doing some burn marks with irons in the early stages of Re-worked without much success as the iron has a safety setting so that it switches off if it gets too hot so my marks were very faint. It was suggested to use some old style irons (perhaps antique) heated up and again using this for branding. I love this image as it shows the variety of marks that can be made from the same type of object.
Another pin on Pinterest to catch my eye was this image (above) by a fellow blogger: Julia Weber
This is a container full of pennies which have been soaked in vinegar for a week which creates a lovely blue stain which this blogger has used for wood. I've been trying to include more colours in the mark making of Re-worked and I think this a lovely way of creating a marking element.