Name: Fe Driver
Source: Alan Yates
| percent | parts | component |
|---|---|---|
| 56.67% | 17 | Potassium Nitrate |
| 20.00% | 6 | Iron (-40+60 mesh, fillings) |
| 13.33% | 4 | Charcoal (airfloat) |
| 10.00% | 3 | Sulfur |
Coat the iron. (i.e. Using the stir-fry or solvent evaporation method.)
Ball mill all accept the metal together to integrate, 10-20 minutes should be sufficient, then screen in the iron. If the chemicals are already quite fine screening alone is sufficient.
6:1:1 Blackpowder meal + 2 part Iron works pretty much the same if you are in a hurry. If using commercial meal you may find 8 parts meal, 2 parts iron, and 1 part 60 mesh charcoal is more useful.
Uncoated iron won't last very long, but if kept dry and used within a few days it is acceptable not to coat the iron. For example, if you just wish to test out the effect you may make and shoot the device in the one day with no problems.
The stir-fry method is quick and easy, just heat the iron in a wok or similar metal dish with a slash of linseed oil. A little excess oil may be added as it boils and evaporated off by prolonged heating. The coated iron will be much darker, almost black, so it is easy to tell if you've added enough oil. The treated metal should then be spread out on a heat-proof surface to cool. If it is tacky you added too much oil or didn't burn enough of it off. It will generally dry in a few days however, linseed oil "drying" is actually an oxidative "curing" process where the oil cross-links and becomes a resin-like polymer.
Paraffin wax may be used instead of linseed oil in a similar way, just shave a candle into the wok while the metal is warm. Try not to heat the metal "dry" for too long it will rust quite rapidly at elevated temperatures, especially if quite fine. If your iron is already rusted a wash with HCl will remove the scale quite effectively, it can then be dried in the wok and coated in one step leaving it clean and reactive under the protective coating.
The coating process may be done cold by dissolving wax in naphtha/shellite or a similar solvent. The exact process is quite similar to making whistle mix. Linseed oil could also be diluted and coated onto the iron cold, but this method is not recommended. Some people toss their iron in excess linseed oil, let it drain, then spread it out and let it cure. This works, but takes about a week to dry completely and is prone to clumping.
The alloy of the Iron is important, pure Iron will be very boring indeed. If you want fracturing sparks like spur-fire gerbs and sparklers you must use steels. The best effect is produced by steel filings of moderate carbon content, alloys typically called "Medium Carbon Steels".
"Mild Steel" produces less violently dividing sparks, the effect of which is basically invisible at typical observation distances. "High Carbon Steel" starts fracturing very early and the effect might be called "lacy", but is generally less attractive than that of medium carbon steel. "Manganese Steels" produce very definite fractures where the particles fork into two or three parts before exploding violently, the effect of which is best observed at close proximity and is similar to Senko Hanabi using pine charcoal. Forget about using "High Speed" and "Stainless" steels, they are very boring, although stainless produces very bright yellowish sparks there is no division at all. "Cast Iron" borings produce an excellent effect which is similar to Manganese steel, but instead of forking cleanly before exploding there are multiple "bushy" explosions. The effect is quite similar to Senko Hanabi using pine soot and is probably the best all-round considering the price and availability of the alloy.
The mesh sizes specified are suitable for smaller devices. Large gerbs and drivers may use much more coarse material for best effect, 10-20 mesh is suitable for 25 mm or larger devices.
Brake drum turnings are a favourite source of material for larger gerbs. The Chinese tend to use "iron sand" or "sandy iron" (not magnetite sand!) which is a (hammer?) milled cast iron rich in cementite that produces wonderful effects in larger devices.