Basically, slow match is made by soaking rope in a solution of nitrate, then letting it dry. I've successfully used both water and vinegar, and I don't doubt that other solution media would work. (Anyone want to try beer?) One musketeer I know uses coffee, as it imparts a nice brown color to his white cotton rope.
I have found that at room temperature the basic ratio is 3 tbsp (that's tablespoons -- the bigger ones) nitrate to 4 cups water. I believe 4 cups is a quart. In metric terms, this means about 60ml of nitrate to 1 liter of water. Others have used less nitrate successfully, one recipe being one film container of nitrate per gallon of water. My guess is that less nitrate results in a slower burn, with consequently longer rope life and possibly lower ember temperature, with possibly a higher misfire rate.
There are a few do's and don'ts:
DON'T
- Boil the solution and saturate it. As the temperature rises, it can absorb more and more nitrate. If you get too much nitrate into the rope, it burns more like a fuse than a slow match. This can be useful if you want fuse, but it burns about ten times faster than you want it to.
- Try to make match in a plastic soda bottle. This is likely to result in uneven coverage with the nitrate solution (see below).
DO:
- Lay the match flat to dry. I once hung it over the shower curtain rod, which made it easy to clean up the mess, but ended up with concentrated nitrate at the ends of the ropes, and very little in the middle. Lately I've taken to letting it dry in the back yard, much to the delight of the grass.
- Make sure the cord is completely covered. If the cord is not completely covered, there will be less absortion in the uncovered parts, resulting in the match going out at a crucial moment, like when people are watching. I suggest using a shallow soaking pan, with something heavy covering the cord to make sure it's submerged. Zip-Loc plastic bags also work pretty well, when you can squeeze all the air out of them. Beware, though: as the solution displaces the air in the matchcord, it floats to the surface and results in some match being uncovered. You'll have to check it ever 15 minutes or so and let out the displaced air. After 30 minutes to an hour, it will have all been displaced, and you don't have to worry about it any more.
- Reuse your solution. Assuming there is not a lot of unsavory contamination in your solution, it can be reused until its gone. I've used the same batch since day one, just adding more water and nitrate whenever I need it. Between batches, I put it in the freezer, where it seems to hibernate happily.