"A friend sent me a link to Whirled Wide Webs, which sells mounted spider webs. They’re lovely, but a tad pricey for what amounts to a glorified science fair project. With a little practice, you can easily make similar mounted webs for next to nothing.
If at all possible, make sure that the spider is done with the web before you collect it; even though they can rebuild a web pretty quickly it still takes them time and energy to do so. If you come across a really lovely web that’s still occupied it’s probably okay to collect it as long as you don’t keep bothering the same spider over and over again.
Stiff paper in contrasting color
Spray adhesive (hairspray will work in a pinch)
Spray varnish or craft sealer
Go watch the rest of the instructions at The Art of Darkness!