Originally Posted by
Linstrum
Assay your charcoal for its ash content. Each and every batch of charcoal will have a different ash content, the amount of ash in wood is not a uniform constant across nature. Besides that, how much ash is in wood varies depending in what part of the tree or plant the material came from.
Stating the obvious, ash does not burn, so, the ash dilutes the fuel content contained in charcoal. I've found charcoal that was 1/6 ash. With that much ash, the black powder made with it was pretty weak, plus was incredibly dirty.
If you shoot, you have an accurate powder weighing balance, and that's the only piece of precision equipment you need. How to find ash content is a pretty simple procedure.
You will need a steel tin can lid like from a large size soup can, a propane torch, a kitchen stove, and some of your charcoal that has been coarsely powdered. Outdoors, use the propane torch to heat the steel tin can lid red hot to burn off the protective coating, and then scrub and wash the lid to get it clean. Weigh out more or less 50 grains of powdered charcoal, and note its exact weight to a tenth grain. Put the powdered charcoal on the tin can lid and spread it around in an even layer, keeping it away from the edge of the lid. Set the tin can lid and charcoal on a kitchen stove burner at just enough heat so the lid is a dull red heat. The charcoal will ignite and glow red hot, and after a few minutes, carefully sweep the charcoal around with the side of a length of wire, like a straightened large-size paperclip. Keep sweeping the charcoal around every few minutes, being careful not to spill any off the side of the lid. After about twenty minutes, there should be just a light gray ash left. Turn the stove off, and when the lid is cool enough to pick up, brush all of the ash into the powder weighing balance pan and weigh it. As an example, if the charcoal sample originally weighed 47.2 grains, and after burning it off on the stove, the ash weighs 1.8 grains, then 1.8 divided by 47.2 equals 0.0381. Multiplying by 100 gives 3.81% ash. Round-off to 3.8%
The math used to compensate for ash content is straightforward. Using avocado wood charcoal with 3.8% ash as an example, the math steps are as follows:
1. 3.8% ash means there is only 96.2% combustible material, 100% minus 3.8% ash leaves 96.2% combustible material.
2. Convert 96.2% to decimal form that is 0.962
3. Mathematically invert 0.962 by dividing 1 by 0.962 to find out how much more ash-contaminated charcoal to add to the black powder mix so it comes out at the correct amount of combustible material. 1 divided by 0.962 = 1.03950. Round-off to 1.04
4. For black powder using the standard 75 parts potassium nitrate, 15 parts charcoal, 10 parts sulfur:
The next step is to multiply the 15 parts charcoal by 1.04 to get 15.6 parts of ash-contaminated charcoal. So, the new black powder formula using avocado wood charcoal is 75 parts potassium nitrate, 15.6 parts of ash-contaminated charcoal, and 10 parts sulfur.
Ignoring rounding-off, the math used gives exact values, they are not approximations.
Compensating for ash below about 2.5% is not worth the bother because other things come into play that affect how accurately the ingredients can actually be weighed, such as moisture content and purity of the potassium nitrate and sulfur. However, there is no harm in compensating for ash content when it is below 2.5% if you care to, I do. The best you can do is make sure your potassium nitrate, sulfur, and charcoal are all dry before weighing them. I am a chemist, and a good part of what I did was pay attention to details when measuring and weighing things.
But one aspect of finding charcoal wood is to find one that has as little ash as possible, since ash interferes with the black powder burning efficiently, plus ash makes hard barrel deposits that are insoluble in water. Depending on the kind of wood, ash usually has calcium salts in it, most often calcium carbonate that is virtually insoluble in water. Limestone is mostly calcium carbonate, as is marble. The worst kind of ash has silicon dioxide in it, which is quartz. It is highly abrasive besides insoluble in water, and forms common window glass when it melts in contact with other components found in ash.
The absolute best woods will produce charcoal with good creosote content when roasted at the right temperature for the right amount of time, with 2.5% or less ash. I seem to recall the lowest ash assay so far was 1.5%, so set your sights on that, but 2.5% to 3% is great. My own cut-off point is no more than 4% ash.
Some of the guys here have been making black powder that performs just as good as commercial, and how they do it has a LOT more to it than the ash content of the charcoal. But ash content does play an important factor that should not be ignored.