Ghost Mines and Colored Flames
Green mines are easy. You mix a teaspoon or two of the firework chemical, boric acid, in a gallon of methyl alcohol and you're set. The boric acid reacts with the methyl alcohol to give you methyl borate, which is volatile. The boron in the colored flame mine gives it a very pronounced green color. The colored flame mine can be burned in an alcohol lamp or in the open (a Sterno can sort of thing). My buddy used a stainless steel bowl placed in a dish full of sand. Of course, once he had green he wanted other colored flames. But, those were a little more difficult.
In order to get a chemical to make a colored flame, you have to get it into the flame itself. And, unlike the boron, it's either tough or undesirable to produce a volatile metal compound. We fussed with that awhile until we hit on the idea of a wick. A piece of steel wool in the bowl of alcohol did the trick. So now we could produce colored flame mines in a rainbow of colors.
The elements chosen are obvious, but the actual firework chemicals are a compromise among solubility in methyl alcohol, cost, and availability. Turns out that roughly 50 grams per gallon always works. In some cases it doesn't all dissolve, but with calcium chloride or sodium chloride, who cares?
- Red: Lithium chloride (actually any soluble lithium salt)
- Orange: Calcium chloride
- Yellow: Sodium chloride
- Green: Boric acid
- Blue: (nothing - alcohol burns blue)
- Violet: Potassium iodide
The next step was to go large. I had been firing gasoline fireballs out of some mortars I had. Starting with a half gallon, I had gradually worked up to blowing three gallons of gasoline out of a six-inch steel mortar using a charge of 40 to 120 grams of FFG black powder for lift. So why not shoot colored flames instead? Several folks at the "Do-It" fireworks event had a chance to witness my first shots of the half-gallon fireball "Lampare Mines." Upon seeing a daytime video of these colored flame mines, Harry Gilliam coined the phrase "Ghost Mines."
I launched some of these at the Western Winter Blast XII using the following gear:
Mortar: 4-inch inside diameter iron pipe, 2 feet long
Lift charge: Place 40 grams of FFg black powder, a pinch of sponge titanium, and an electric match in a very small zip lock plastic bag. Squeeze all the air out, and tightly wrap it with both clear packing tape and then masking tape to seal it against alcohol seeping in.
Fuel: One gallon of methyl alcohol with 50 grams of firework chemical coloring agent
Method: Fill mortar with alcohol and firework chemical coloring agent solution. Lower the black powder charge into the mortar. If the charge is tightly packed it won't float. From the friendly end of a 50-foot electric shooting wire, fire that thang!
Drawbacks: Typically there is some burning alcohol left behind in the mortar: HDPE and paper don't last too long.
Supplies: I get the methyl alcohol at the local lab supply, or fancy hobby shop, for $10/gal. Ethyl alcohol may work on some but the denaturing agent tends to give a yellow colored flame. I hear the boric acid doesn't work with ethyl alcohol.
No Man's Land: To get a really beautiful sky-blue colored flame, add six grams of copper chloride and 200 ml. of methylene chloride (chlorine donor) to the gallon of methyl alcohol. Great colored flame but it also makes a phosgene byproduct, something you might not want indoors. Any chlorine donor will do that. That is why I shied away from strontium and barium.
References: Unfortunately after pulling this stuff together I found out it was also in Weingart and in an early issue of Pyrotechnica. Well, at least when you reinvent the wheel there is some satisfaction in knowing that it came out round.
GHOST MINES, REDUXChris Spurrell, who wrote the very interesting Ghost Mines article above, sent along some pix of colored liquid fires we thought you might enjoy. Ghost Mines are basically flame projectors, which use flammable liquids to produce colored fire. They are very different from most fireworks you have ever seen, often times producing a very eerie looking effect. Although pictures don’t quite convey the "look" of these effects, I thought you might enjoy seeing these.
This first one shows Chris using a pump spray bottle from Home Depot, filled with methyl alcohol with lithium chloride dissolved in it. Nice, typical lithium color, different from a strontium red.
Lithium chloride dissolved in methyl alcohol from Home Depot pump spray bottle
The next picture also shows lithium chloride in methyl alcohol.
Lithium chloride colored flame
Other colored liquid flames look good as well. The picture below was taken of different flames produced at the 2002 Western Pyrotechnic Association’s "Do-It" event. Chris created this beautiful effect by putting about a quart of the colored flame juices into stainless steel bowls set on the ground and then lit. He puts a couple of steel wool pads in each bowl to serve as wicks.
Art, ain’t it?
From top to bottom:
- Black Powder, FFg
- Boric acid (CH8042)
- Calcium chloride
- Copper chloride (CH8091)
- Electrical Firing System
- Electric matches (GN5051)
- Lithium chloride
- Methyl alcohol
- Methylene chloride (CH8193)
- Potassium iodide
- Sodium chloride (table salt)
- Shooting Wire (GN5010)
- Steel Pipe, 4" ID
- Steel Wool
- Titanium, Sponge