I've done quite a bit of distressing/weathering leather for costume pieces.
These involved soaking an area of leather with Rubbing Alcohol, then roughing it up with sandpaper.
Since the leathers had a fairly thin surface layer of brown dye, taking that layer away (usually in the high spots) lightened those areas did a good job of simulating wear.
But! On the Labhran site there are new sporrans which have been "aged" in a non-distressing non-invasive way.
Since the outer layer of leather isn't being removed that means it's a matter of colouring the leather.
From my experience, and seeing the work of others, it appears there are two basic approaches:
1) if starting with light-coloured leather (or vinyl) paint it dark brown, then before the paint gets too dry rub off the paint from all the high areas, leaving the crevices and low areas dark. This method doesn't work if the leather pores are open; the paint will soak into the leather and can't be rubbed off.
2) if starting with dark leather (or vinyl) do "highlight passes" of a lighter colour paint. The tricky part is applying the paint when it's nearly dry, and making sure it's evenly applied to whatever you're using to apply it, so there's no blobs to make a splotch of the lighter colour on the leather. I use an old rag that's wrapped around a round sea-sponge, which applies a very subtle light brushing of paint with no harsh edges or blobs.
It's possible to have two nearly identical-looking pieces which were done with these opposite methods.
Now for my sporran project, first I did a test on some scrap leather, then I did a test using a sporran I picked up cheaply on Ebay.
On the left is the plain way it came, on the right is after doing some "highlight passes" with a mix of lighter-brown paint to simulate age and wear. On the cardboard you can see the colour I used, a reddish brown.
It fools the eye into thinking that wear has taken off the outer dyed layer in places, showing the lighter leather beneath.
This was just a test; the end goal was to "age" or "antique" my Margaret Morrison bespoke sporran, a re-bag for the lovely hallmarked Sterling Silver hinged cantle I got on Ebay.
On the left is the plain dark leather as it came, which I feel lacks character and soul. On the right is the result, which I feel is more befitting the 60-year-old cantle. I should mention that in person the weathering is far more subtle than it appears in the photo, and from a distance the sporran's appearance hasn't changed all that much. It's when you're closer that the character appears.
