Name: Senko Hanabi
Source: Takeo Shimizu (et al)
| percent | component |
|---|---|
| 60.00% | Potassium Nitrate |
| 24.00% | Sulfur |
| 16.00% | Charcoal (pine, airfloat) |
Senko Hanabi composition goes a long way so grinding in a mortar and pestle is probably the most practical preparation method, especially while you are tuning the composition to your particular charcoal.
Twisting a small quantity up in some tissue paper (like Chinese fuse) is the basic construction method. You can dip the end of the twist in Potassium Nitrate solution to make it a touch-paper fuse, and twist the composition-free end up for a few inches to provide a handle. The alternative is to add an aqueous binder and dip-coat thin slivers of bamboo, rushes, dry grass or other thin wood sticks.
It is important not to put too much composition in each sparkler, Shimizu suggests 90 mg per device. Using too much will either blow the droplet off the end of the sparkler or make it too large and heavy to stick.
I've classified this composition as a glitter because it shares its basic polysulfide chemistry with true metallic fuelled glitters. It is a tuned version of this reaction:
2(KNO3) + 2(S) + 3(C) => K2S2 + N2 + 3(CO2)
Which gives an approximate composition of:
67 Potassium Nitrate
21 Sulfur
12 Charcoal
Excess Charcoal and Sulfur are provided in the practical composition to ensure some Charcoal survives to react with the polysulfide dross and to make up for Sulfur loss due to evaporation.
The charcoal is very important. The effect varies depending on the kind of charcoal you use, although the composition shown is fairly forgiving of poorly suited charcoals. Pine charcoal is the best bet as it performs very well and is cheap and easily available.
Some suggest using sugar charcoal or lampblack. I find lampblack in particular interesting, depending on the source very different effects can be produced, but most lampblacks will produce no sparks at all. Experimentation with lampblacks and charcoal mixtures is for patient and determined pyros only! Hint: Hot-BP charcoals (Willow, Hemp, Bamboo, Balsa, etc) are usually quite terrible for this effect but in small quantities can do interesting things.
Adding sulfides, oxides and carbonates to the mixture is something I'd like to experiment with, but there are so many different combinations it could take years.
I generally use my mini ballmill to prepare it. The mini-mill can process ~ 10 g batches of composition in a small PP jar with lead fishing sinkers at good efficiency. About 20 minutes is all it needs, excellent for quick test batches while tuning this very beautiful effect.
I find kitchen sandwich wrap paper works quite well for making the twisted variety. Dextrin is not the best binder for the dipped variety, traditionally glutinous rice starch is used, but common laundry starch or CMC seems to work well (better than yellow dextrin anyway). Dextrin will still work, but it seems to diminish the effect somewhat. Adding a little extra Potassium Nitrate might offset the Sulfide loss but the water liberation from any carbohydrate binder changes the melt chemistry significantly.
Senko Hanabi devices are very cheap and easy to make. They aren't very dangerous and can provide quite a tuning challenge. They are also a sensitive test for your charcoal quality and properties, the reading of which is an fascinating and useful skill.