Assay charcoal for ash content, do not heat charcoal wood too hot
Hey, you guys have progressed a long way! Doing good!
I started making black powder in 1965 using charcoal I made from fir lumber because I didn't have any black willow. I used it in a muzzle-loading 1-inch smooth-bore canon my dad machined from a 3-inch diameter bar of SAE 1045 carbon steel. It went “BOOM” pretty loud and would shoot a one-inch ball in one side and out the other of an old wrecked car, so my fir wood charcoal black powder was good enough for that. The black powder was simply made by milling the potassium nitrate separately from the charcoal and sulfur, mixing everything damp as a paste, screening, and then drying. I knew it wasn’t even close to commercial stuff, but it did what I wanted it to.
I'm a chemist, and when I got done with college in 1975, I used what I learned. I still didn't have any black willow, though, so I investigated everything I could lay my hands on where I lived in Southern California, from all the kinds of native trees and shrubs, plus ornamental plants and trees that had been imported from everywhere else. About the only thing I didn't try was poison oak. Right off, I found out all the bamboo and grass species I tried were pretty bad.
I found a few sources that seemed like good candidates, but when I burned the charcoal, there was often a lot of ash left behind. So, I started assaying my charcoal for how much of it would not burn.
I found one particular 6-foot tall straight-stemmed feathery plant called fennel (foeniculum vulgare), sometimes mistakenly called anise, native to Southern Europe and the Mediterranean, which smells like licorice. It is a nuisance weed that grows everywhere along the Southern California coast. It made what seemed like the ideal charcoal that was light and fluffy, which I could pulverize with just my fingertips. But at only ~84% combustible material, it had unacceptable amounts of ash that interfered with fast burn, plus left hard gun barrel residue. But I made a test batch of black powder with it anyway, by adjusting for its 16% ash content. See later on for the mathematics involved, it’s not hard to do.
Assay your charcoal. 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%
I don't use charcoal with more than 4% ash.
One more thing I was investigating was how hot to roast wood. High carbon content charcoal that conducts electricity does not make the best black powder. Using a temperature sensor inside the wood roaster to keep the temperature from going too high should be done so the wood doesn't decompose too far. How hot and how long wood roasts is important, because the creosote from partially decomposed lignin, cellulose, and all the other carbohydrates related to cellulose, like sugar, are a major part of what makes the best black powder. When the wood gets heated too hot, the "good stuff" volatilizes and leaves hard carbon behind, so what is left is "dead burnt" charcoal.
In about 1804, Monsieur Éleuthère Irénée du Pont de Nemours became the master black gunpowder manufacturer in the United States, which was just four years after he arrived from France in 1800. He personally had the knowledge of both the art and chemistry needed for manufacturing black powder that he had learned in France. The art part were things like not having a thermometer to know how hot the wood was while it was roasting, instead being able to “read” the flame characteristics of the burning wood vapor coming out of the wood roasting retort. I would think that du Pont very quickly planted stands of European black willow in Delaware for making his black powder, although grapevine, along with our four related species of rather abundant North American cottonwoods have been very successfully used at one time or another. The Confederate States used Eastern Cottonwood for its black powder industry during the Civil War. Grapevine is still currently used. Cottonwood is still used in Mexico, especially by their fireworks industry.
The math used to compensate for ash content is straightforward. Using my fennel charcoal from above as an example, the math steps are as follows:
1. 16% ash means there is only 84% combustible material, 100% minus 16% ash leaves 84% combustible material.
2. Convert 84% to decimal form that is 0.84
3. Mathematically invert 0.84 by dividing 1 by 0.84 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 0.84 = 1.190476. Round-off to 1.19
4. The next step is to multiply the 15 parts charcoal by 1.19 to get 17.86 parts of ash-contaminated charcoal. Round-off 17.86 to 17.9 parts charcoal. So, the new black powder formula using fennel wood charcoal is 75 parts KNO3, 17.9 parts of ash-contaminated fennel charcoal, and 10 parts sulfur
In my replica .36 Navy Colt, my fennel black powder did okay, but nothing even close to the du Pont ffffg I purchased back in probably 1973. That's what 16% ash does in black powder charcoal, it makes "just okay" black powder. I never used fennel again for firearms, but black powder made with it does have its uses, like for making your own quick match for cannon touch holes. For just that one purpose, fennel black powder burns slower, but ignites easier and burns smooth and steady.
I never had any black willow, but I did have “Jim Bacon” and “Hass” varieties of avocado tree wood that are both fairly soft but tough woods. The avocado woods I used assayed between 3% and 4% ash, very much lower than 16%. One year aged avocado wood has been my go-to charcoal wood. To adjust for 4% ash, there is 96% combustible material in the charcoal. The mathematical inverse of 0.96 is about 1.0417, round off to 1.04, and then that multiplied by 15 parts charcoal comes out to 15.6 adjusted amount of avocado charcoal to use.
To test charcoal to see if it conducts electricity, I use an electrical circuit testing ohm meter set at 20,000 ohms to check sticks of charcoal. How far apart the test probe tips are, and how hard they are pushed against the charcoal, are all part of it. Make sure you aren't touching the circuit test probe tips because you conduct electricity, too. I don't remember what resistance readings I got, but if the readings are low, your charcoal was heated too hot and too long. Low readings indicate your charcoal is a good conductor of electricity, a bad thing for making good black powder. "Dead burnt" charcoal conducts electricity quite well, Thomas Edison used charcoal strips made from bamboo for his first commercially successful carbon filament light bulbs!
So, what I did to make the best black powder I could was find a wood that made light fluffy charcoal with less than 4% ash. I checked my charcoal to be sure I didn't heat it too hot by using an ohm meter to see that it did not conduct electricity. I compensated for the ash by increasing the weight of the charcoal in the black powder formula. As far as ash content goes just by itself, it causes two problems. It interferes with black powder burning efficiently, and it decreases the amount of available fuel.
I live in south central New Mexico now, where there are both Fremont and Narrow Leaf cottonwood everywhere. Both look promising from the minuscule amount of ash left from burning a sliver of the wood.
Assay your charcoal for ash content. Finding out that 1/6 of your charcoal is not charcoal may be a bit of an unwelcome surprise!