This little gerb project is from The Best of AFN III (BK0011). It is part of a larger article entitled "Micro star Bursts-Without Micro stars." Thanks to Jack Drewes at AFN for letting us reprint it here.
An anonymous booklet of formulas from E. D. Chemco under "BLUE STEEL FOUNTAIN" refers to a "crackling titanium effect;" "crackling," eh? But the same titanium flakes mixed with Meal-D powder or whistle pyrotechnic compositions gave just "plain" sparks. Nor were micro star bursts seen with steel or aluminum. I don't know what variations in the red flame powder will do to the effect, or what I'd get with a choked case, or with solvent-dampened pyrotechnic composition. Presumably the incandescent titanium flake, without benefit of a cast micro star around it, rises through the flame and develops a crust derived at least in part from the powders or pyrotechnic composition products. Gas within this crust then explodes through. It's a pretty effect, simply produced. Following is from the booklet, "Formulas" by Ed Moore.
Blue Steel Fountain (Gerb)
Parts/Percent by Weight
Steel, fine powder
The pyrotechnic composition is tamped lightly into a choked case, 1/2" ID with a 1/4" wall. If a small amount of titanium is added to a portion of the composition and that composition is charged into the tube first, then the regular composition next, the effect is to change from a delicate steel to a crackling titanium gerb.
Gilliam's comments on this gerb
When I made these gerbs, I played with substituting all kinds of metals and percentages thereof. I eventually settled on coarse titanium flake as my spark of choice. But I also like the iron-to-titanium effect change, and also experimented with color changes. If you use iron or steel, try our CH8300 Sparkler Grade Steel.
Substituting barium carbonate to make green, or strontium carbonate to make red can change Gerb flame color.
I first made these gerbs using the same tubes hand cut from TU1065. I didn't have proper fountain tooling so I was using a dowel to ram a 3/4-inch-thick dry bentonite clay (CH8078) plug. Then I rammed the composition in, topped it off with another clay plug, and then lightly drilled (hand drilling, not electric) a 1/4" wide hole thru the clay into the composition. I then just stuck a couple of inches of visco fuse into the hole, lit it and got back. Blew up every time.
What eventually worked was using a real, fountain tool. I surmise that the solution lay in the fountain tool's shaping of the venturi-like nozzle on the inside of the gerb. The clay plug is slant-shaped so as to direct the gasses and sparks toward the outlet. This is a pretty violent gerb, as gerbs go. After I switched to using real fountain tools for this particular gerb, my explosions went away. Well, almost went away. I was also successful at making them explode by increasing the titanium percentage to higher than 15%. So I reduced the titanium percentage back down to 12 and everything was cool again.
I also later re-read the article above, particularly the words "lightly tamped" regarding packing the pyrotechnic composition into the gerb tube. It would be safest if these gerbs were made with a press, using an arbor or hydraulic press. These gerbs are fun and make a spectacular quick and uncomplicated project.