Slow match
From PyroGuide
Early firearms were fired using a heat source (such as burning tinder) introduced via a simple touch hole in the barrel wall. Later, a priming charge was added, consisting of loose powder poured into a flash pan could be ignited with a slower-burning, less intense ignition source. Slow match was an easily-produced, portable, long-burning igniter that also had some limited resistance to humidity and wet conditions. The matchlock musket survived the invention of snaphance and wheel-lock designs, before being succeeded by the flintlock in Europe around 1720 and in Asia in the 1900s. Improvised matchlock firearms were utilised by pro-Indonesian militia in the unrest leading up to the liberation of East Timor in 1999.
Nowadays, slow match can make a reliable long-delay fuse (or a shorter alternative to blackmatch that doesn't "spit"), or a long-burning medium for smoke mix. Obviously, the most useful characteristic of slow match is its slow, regular burn rate of between 20 and 150 cm per hour, depending on manufacture. It can also be made to burn without emitting sparks.Slow match can directly ignite fine, loose black powder, graphite powder, red phosphorus, and compositions containing chlorate and permanganate oxidisers. For other compositions, additional priming will be required.
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Production
Chemicals
Three chemicals have been used historically to create slow match. Potassium nitrate (KNO3), the most widely used, is considered to be the best. Sodium nitrate (NaNO3) also produces good results, but is hygroscopic, and therefore more difficult to store and less reliable in the presence of moisture. Lead acetate (Pb(CH3COO)2) is not recommended at all, as its toxicity produces all sorts of production and handling problems.
Other additives suggested include lye, acetic acid, citric acid, bicarbonate of soda, sucrose and starch. By changing the pH of the solution (with NaOH, etc), the purpose is to improve the absorption of nitrate, thus making the slow match more reliable and weather-resistant. Sodium hydroxide (lye), however, is very hygroscopic/deliquescent, and this fact would negate any other advantage. Potassium hydroxide (KOH, aka potash-lye) would be a better choice as it has a lower affinity for water.
The addition of vinegar (acetic acid, CH3COOH(aq)) has been shown to increase the burning rate of slow match by about 14%, but has an eye-watering smell which is only made worse by combustion. A better option would be citric acid, which is in fact used to increase the burning rate of cigarettes.
Sodium bicarbonate is used as a moderant, meaning that is is added to control the speed and heat of combustion. When bicarbonates are heated, they produce carbon dioxide which slows combustion by displacing oxygen. The reaction is also endothermic, which helps to immediately control excess heat. There would be no point trying to use both acid and bicarbonate in the same solution.
Sucrose (or dextrose, or lactose), starch and sometimes ammonium chloride (NH4Cl) can be used to increase the amount of black/grey (organic) or white (inorganic) smoke released. Starch especially SGRS does impart a level of moistureproofing to the finished product. Be aware that ammonium chloride decomposes into ammonia and hydrochloric acid: both nasty irritants.
Cord
Historically, hemp rope or cord was used for the manufacture of slow match. A common working alternative (though more expensive and believed less effective) is braided cotton cord. Manila and sisal have also been suggested. Make sure that the cord does not have a nylon core, or any nylon/polyester fibres (i.e. must be 100% cotton).
Although braided cord is recommended because it is just plain tidier, ordinary twisted rope has been used with some success. If properly treated, twisted-rope slow match will burn faster than it unlays (untwists). Regardless of the type of cord used, it is recommended that you test-burn a sample to determine if there is any tendancy to unlay, curl or twist when burning.
Method
Making slow match is essentially a matter of soaking the cord in the solution, then drying. The best method to ensure the most consistent final product is as follows.
- Prepare the following solution: 60-120ml potassium or sodium nitrate in 1 litre of water. The solubility of KNO3 in water is 357g/l, and 920g/l for NaNO3, but do not try to saturate the solution. Using a highly concentrated solution will cause the slow match to burn faster than intended and to "spit".
- Pre-soak the cord in water before adding it to the nitrate solution. Dry cord often contains enough air to make it float. Uneven absorption of the nitrate will cause the slow match to burn erratically and to extinguish itself unexpectedly. Making sure the cord is good and waterlogged will ensure a better product. The cord may also be treated with lye or acid at this stage.
- Soak the cord in the nitrate solution for upto 24 hours. The primary variable that will determine the burn rate of the match is the length of time for which it it soaked. Experimental evidence suggest that there is no measurable advantage to soaking the cord longer than 24 hours.
- Lay the slow match flat to dry. It has been found that hanging the wet match vertically will result in nitrate concentration at the ends, resulting in uneven, unreliable burning rates in the product.