decorative items like skulls
cheese cloth or any thin, thready material
glue gun or epoxy
Part 1: Haze the Jars
It's very simple to age jars. First, soak them in hot soapy water. This not only cleans the jars but softens any labels they might have.
Most labels won't come off in one try. When it softens (and this could take 30 mins to an hour), peels off as much as you can, then put them back in the water.
If it has stubborn glue residue, steel wool works great.
Now that they are all nice and clean, it's time to get them dirty. Pour about an 1/8 to 1/4 cup water into the bottom of the jar, add a squeeze of white glue, stir, and roll the jars to coat the sides. Pour the glue mix from one jar to another, turning each one to create a nice glaze.
After the initial cloudy stain, mix a touch of brown paint with a bit of white glue and water it down, just like the first step only this time, make the brown darker. Swirl it around the bottom of the jars and turn each one so a few streams line the sides.
Mix some white glue, black paint, and some water together to create soot or grime stain at the top of the jar. Dip a piece of cloth in the mix, then dab it along the inside rim and top of the glass. Dab, smooth. Dab, smooth. Dab, smooth. When they dry, if some have a bit too much black, it easily wipes away with a bit of water (I just used my fingertips).
Part 2: Decorate
Take your material, wrap it around the outside rim of the jar, and tie it with a knot, snipping the ends off.
Mix black paint and water with white glue, and brush it over the cloth.
To finish them off, I took a collection of skull castings I'd been saving. I coated the back of them with quick-drying epoxy, and stuck them to the outside of the jars (you could use a glue gun to attach your decorative item them if you don't have epoxy but it will eventually fall off).
Because they are glass jars, you can put actual tea light candles in them. I chose, instead, to create a number of LED candle stubs.
This same process is used to make organ specimen jars with plastic props and watery red paint. You'll see it again in my ingredient jar tutorial.
You are only limited by your imagination.
Good luck and happy haunting.