Originally Posted by
Linstrum
indian joe
Thanks for asking about ash, my apologies for taking so long to respond, along with such long answers. I hope you can muddle through what I have.
There are two problems caused by ash.
The first is that it interferes with the charcoal burning.
The second is that it contributes to hard barrel deposits.
Question 1) how much (if any) difference does the way we do our burn (cooler burn, hotter burn, over done, brown instead of black etc) make to ash content % - given the same source of wood?
The short answer is very dark brown charcoal (but how dark brown depends on the kind of wood, too), the kind that has been proven to give the most energy content to black powder. That grade of charcoal delivers the highest gas volume per unit of weight, while still burning hot. High gas volume and burning hot gets particulates out of a gun barrel most efficiently, since particulates are what make barrel deposits. Barrel length plays a part in that, too, when a projectile leaves a short barrel, the temperature and pressure are still very high, so, the particulates are at a very high velocity and literally don't "stick" around.
I don't know exactly what the chemistry is of ash deposits in gun barrels. I could figure that out quite easily IF there were only two chemical species present. But there are potassium nitrate, charcoal with creosote that contains dozens of chemical species, and sulfur; all of which can react with the calcium salts, magnesium salts, sodium salts, chloride, and silicon dioxide that may, or may not, be in ash (depending on the wood used for charcoal). The reactions depend on temperature and pressure. Because there could be calcium, magnesium, potassium, sodium, silicon dioxide, carbonate, and chloride present all at the same time when the temperature is around 3,000º F, a glass will form. There won't be much glass formed for each shot fired, and most of the glass will just be part of the gunsmoke in the form of colloid-size droplets, but some will condense inside the barrel. I doubt very much if this enamel-like glass material actually bonds to anything like enamel glazing does, but as you already know, it can be quite hard. It is just something else that mixes in with the other components of powder residue. However, unlike some of the other components, it is not water soluble.
Disregarding ash, I do know that barrel deposit material that forms when black powder burns consists mainly of potassium sulfide, potassium carbonate, some unburned charcoal, and some potassium sulfate.
Using the same lot of wood to make charcoal, ash will likely cause fewer problems with a very dark brown charcoal because of more gas volume to "blow" particulates out of the barrel. I would suspect that the higher the temperature, along with having a high pressure to go with it, would decrease problems from ash deposits by virtue of just plain getting combustion products out of the barrel as fast as possible. Along that line, I'm taking an educated guess that short barrels may have less of a problem with any kind of deposit than long barrels. Long barrels allow the pressure to drop, when pressure drops, gas cools, and when gas cools, molten potassium sulfide micro-droplets form into solid potassium sulfide residue. Potassium sulfide also has an unusually low boiling point of 1674º F AT ATMOSPHERIC PRESSURE, which as a temperature reference point is below the melting point of copper that is not all that high. Use charcoal with as high of a creosote content as is practical. Keep in mind for charcoal that the higher its carbon content the hotter the black powder burns, but the higher the creosote content the more gas volume. So, the cross-over point has to be determined between dead-burned charcoal and having too much creosote. This is why wood roasting temperature, along with roasting time, are so critical.
Something to think about is there is no "rule" that says the charcoal used for making one batch of black powder must be made from all one kind of wood. Along with that is there is no "rule" that says that all of the charcoal used for making that one batch black powder must be roasted at the same temperature and for the same amount of time. Think about mixing and matching different kinds of woods and the different kinds of charcoals made from them, so you get a mix of hot-burning charcoal with some that has a bit higher creosote content. It may not be possible to make the ultimate black powder by using just one species of wood, and roasting whatever kinds of woods to obtain the best kinds of creosotes. Creosote is NOT just one chemical compound, it has dozens of components that vary according to the wood and how hot and long it was roasted. NO ONE I KNOW OF HAS WORKED ON MAKING THE BEST KIND OF CREOSOTE - - - AND I HAVEN'T, EITHER. Creosote, depending on the kind of wood, ranges all the way from turpentine (like for cleaning paint brushes) to hard gummy black tar. Its characteristics depend on the final roasting temperature of the wood, and how long the wood was roasted at what temperature. It isn't simple, but in general, the lower the roasting temperature the greater the charcoal's gas-generating ability, while the higher the roasting temperature the higher the charcoal's burning temperature. The conundrum is that the higher the flame temperature when black powder burns the higher the gas volume is because gas expands with heat. But when a lot of gas is generated from creosote alone, the gas generation cools the black powder while it is burning. There is a cross-over point or Goldilocks Zone where the amount and kind of creosote in the charcoal will be "just right", like Goldilocks said. Many of you have already noticed that some batches of your black powder are outstanding, but you don't know why. This is one of the reasons.
Question 2) would you agree? that the chemistry of the ash make as much difference (maybe more) to barrel fouling characteristics as the actual ash percentage or no?
What is in ash varies according to plant species, but beyond that I haven't been able to find a lot of information regarding any specific plant species, except for grasses that have a high silicon dioxide content. Most ash has calcium carbonate, along with some potassium carbonate and sodium salts. There can be lesser amounts of magnesium carbonate, and sometimes silicon dioxide. There are trace amounts of other things, such as chloride, iron, phosphorus, manganese, zinc, copper, chromium, molybdenum, even cobalt, but don't worry about those because they are in such minute amounts. As far as the chemistry, calcium and magnesium tend to form insoluble deposits that are the most difficult to remove with water, but can be removed with acidic solutions. Silicon dioxide is not readily soluble in anything, except hot concentrated lye solution. Potassium salts are all water soluble - virtually all potassium comes from the potassium nitrate in the black powder, not ash. Disregarding any ash, barrel residue that forms from the potassium nitrate reacting in the black powder is mostly potassium sulfide, which reacts with water, and its products are water soluble. The potassium nitrate from the black powder also forms some potassium carbonate, which is highly water soluble. When potassium sulfide dissolves in water, some amount of hydrogen sulfide gas is produced, which is extremely poisonous, and is what makes black powder gun barrels smell so bad after firing. After firing, there is enough moisture in the air to form the hydrogen sulfide gas that can be smelled in the parts per billion range in air - that's part per BILLION. Since we are all still alive, don't worry about hydrogen sulfide gas, even the Civil War canoneers who burned pounds of powder per shot survived. However, don't use vinegar in a badly fouled barrel without good ventilation, since acidic solutions will produce hydrogen sulfide gas in toxic amounts when a lot of potassium sulfide fouling is present.
There is a lot more to ash chemistry that depends on black powder combustion chemistry, which is not completely understood. So, over-all, who knows what goes on.
The other thing about ash, when it is in the form of mineral particles inside the structure of charcoal, is that its physical presence interferes with the charcoal burning.
When the wood or plant material was growing, the ash minerals were part of specific kinds of cell walls that function as strengthening, defensive, protective, reproductive structures, microtubules, leaf surfaces, etc. Some parts of a plant are very high in ash minerals, such as leaves, bark, roots, and seeds, while the rest of the plant is much lower.
In some, but not all, fast growing plants, specific minerals are used as part of the plant structure in place of cellulose and lignin, since the plant can get minerals for free from the soil, instead of the plant having to synthesize more cellulose and lignin in order to grow quickly. When the wood is heated and decomposes into charcoal, the ash minerals act like an unwanted fire retardant for the charcoal. The mechanism of how it does this is not known, just that the higher the ash content, the more it interferes with black powder having a fast, high-temperature burn.
The degree that ash interferes with charcoal burning is all out of proportion to how little ash there is.
The next part I'm just taking an educated guess.
As far as a mechanism for ash interfering with charcoal burning, it could be that the ash minerals somehow form a barrier on the charcoal particle surfaces down at the molecular level, where a tiny amount of the ash minerals form a thin coating. An analogy might be like a fire retardant paint on a piece of wood, where a tablespoonful of paint can protect a very large piece of wood. The amount of fire retardant paint might constitute just 5% of what's there, but that 5% does a lot to slow down the other 95% when it's burning.
So, assay your charcoal for ash content and keep it below 4%, below 2.5% is ideal.
If you can, assay your charcoal for creosote content, too. I haven't worked out the easy-to-make-at-home equipment for that, yet, because unlike doing an ash assay, the charcoal sample absolutely has to be out of contact with air while being red hot for about 30 minutes. However, Brimstone has mentioned doing creosote assays, perhaps he's figured out something already.
Well, these are far from the best answers and some are at the very limits of my experience. But, hey! You guys have been doing great!
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Yep. Another rabbit hole just opened up to fall down and wander around and maybe get lost in. But this thread has been going on for coming up on twelve years now, and it is finally get to the point of being fine-tuned. TWELVE YEARS to get here, too many of those years stuck at using water filter charcoal, laboratory charcoal, pyrotechnic charcoal, dead-burned charcoal, and worst of all, barbecue charcoal. 
