I recently was asked to put together a fake fire effect for a small community theater. They wanted a fireplace full of burning embers, not a full flame effect that can be done with flame lights. To create this effect you basically need two things: a light source that flickers like a flame and something translucent that looks like burning embers that will flicker in the light.
I initially did some searching for fire glass to see if there were any readily available products to simulate burning embers, but didn't have any luck finding anything that looked realistic enough. Eventually I came up with the idea of trying to make my own, and with a little more research I came across a handy tutorial that demonstrates how to make fake ice cubes out of plastic. I ended up using that as a template for making my own fake burning embers, expanding on the concept by including colored plastic in my fake ice cubes. Here's a quick tutorial:
Go to your local hobby shop and purchase some clear plastic beads. Kyle, the guy behind the ice cube tutorial bought his at WalMart. I found mine at AC Moore, a craft store chain with stores all along the East Coast.
Get some sheets of lighting gel, preferably a few different shades of orange/red. If you don't have a ready supply of gel then you can order some on-line from places like Production Advantage. Depending on how much you need to make you might not need entire sheets of gel so you might want to see if you can get one or more companies to send you a sample swatch book for free.
You'll want to shred the gel(s) into small pieces in order to mix it up with the plastic beads. I ran a few small sheets of orange & red gels through my paper shredder:
Make some forms out of aluminum foil in various shapes (you don't want all your embers to be 100% identical). I used things like batteries, a flashlight, and small cardboard boxes as forms, wrapping aluminum foil around them. Then fill the form up with a mix of plastic beads and strips of the shredded gel. Don't overdo it with the gel, at least at first. You probably want to experiment a bit to figure out the right mix:
Fill up the form with more plastic beads, then place it in an oven at 400 degrees for approx. 20 minutes. You should keep an eye on it to make sure the form doesn't leak and the beads are melting. If the beads aren't fully melted after 20 minutes just leave them in the oven longer and consider turning up the heat slightly. The gel strips have a much higher melting point (after all, they have to sit directly in front of 1000 watt stage lights for long periods of time) so don't be surprised if they don't melt like the beads to. The color should still spread out throughout the mold as the beads melt.
Once the beads have melted take the mold out of the oven and give it plenty of time to cool. Remove the foil and you should end up with a translucent block of plastic:
If you're not happy with your first attempts then don't fret. You can always break up the plastic blocks using a hammer and then melt them down again in new forms. Add more beads and/or pieces of gel to get them to look more like what you want.
The next important aspect of making a good fake fire is making a good flickering light effect. If you're doing this in a theater and you have a good quality DMX-based lighting system you might be able to program an effect to simulate this, but that's a lot of work and can be a hassle if it has to be added to multiple cues. After hunting around a bit I found a product called FauxFlame which is an electrical device you wire to an incandescent light to make it flicker randomly. I bought a couple of these to add to my inventory of lighting toys and wired them into a couple electrical boxes so I can plug any light into them that I want.
The theater had an existing hearth with a few lights mounted inside it. I installed a couple regular household incandescent bulbs wrapped in orange/yellow gels in the hearth, then put a dozen or so plastic embers on top, along with some fake fireplace logs that were bought from a local hardware store. The lights were plugged into a FauxFlame and the result is quite impressive. Here are a few photos and a link to a video showing the effect in action. The set isn't complete yet, so pardon the appearance of the fireplace.
And here's a video of the fireplace in action: