One of the most popular finishing techniques for old prop documents is burning the edge. As soon as people start Googling ways to age paper they'll inevitably find it as a recommended technique. Because, you know, old documents all have burned edges.
No. No they don't.
The whole "burn the edges" thing is an attempt to recreate the edge darkening of improperly stored documents. Initially, it was based on the edge damage common to old parchment stored in an uncontrolled environment. Changing moisture levels cause the edges to contract, producing a darkened edge. Oxidation also becomes a factor. Just like any other leather, parchment darkens over time as the proteins in the material react with the oxygen in the atmosphere. As an example, here's an actual old parchment document from the NSW document conservation facility in Australia:
Trust me, those edges weren't burned. This is where the whole darkened edges = old document thing started, but it didn't end there.
A similar process happens in paper documents. The surfaces exposed to the atmosphere darken as the wood fibers react with oxygen and airborne contaminants. There's also some wicking involved. As room humidity climbs the
paper absorbs moisture. This process happens from the outside in-
the exposed edges and outer sheets of a bundle of documents pick up more
water. When the humidity drops the process reverses. The edges and
outer sheets dry first. This draws the moisture in the interior of the
bundle out to the edges, bringing with it any dirt, oil, and soluble
pigmentation. Tada! More edge darkening.
Somehow, reproducing that look with flame has become a go-to technique. Why? This is purely a theory, but I suspect it dates back to treasure hunts at summer camps. They're a fun way to teach kids the basics of land navigation, and theming the event with a pirate map is just the kind of thing campers love. The problem is that each team needs a map of the campsite. What's a harried camp counselor to do? Trim down one of the pre-printed maps inside the camp brochure, dip it in tea to recreate the look of parchment, and burn the edges because, you know, that's how old maps in pirate movies looked.
So what's the point of this rant? Stop burning the edges of prop documents. It's dangerous, messy, and, ultimately, pointless. If you really want to reproduce the darkened edges of old paper or parchment use the slow dry technique. It's far more controllable, produces a realistic effect, and won't set your house on fire. And check this out for how to reproduce the look of more extreme edge wear.