Black Powder Manufacture

From PyroGuide

Pucks of high performance BP, pressed and dried, showing a density of 1,7g/ccm

Black powder (or gunpowder) in all its varieties undoubtedly is the most essential pyrotechnic material and no serious pyrotechnician can get on without. If we consider amateur pyrotechnics being more than making sparklers or basic fountains and lighting stars on the ground, we will have to draw our attention to one special question: How can I manufacture suitable black powder my own?

Many of us once got the shock of their pyro career comparing the performance of homemade powder with commercial and asked themselves: How the hell can the same chemical compound perform in such a different manner? Such experiences often initiate lifelong quests for fast powder.

Manufacturing high performance black powder is a skill best acquired at the very beginning of one´s pyro career. Having handy good gunpowder will crack numerous possible performance problems. However, numerous pyros seem to skip adopting such skills and there is a certifiable (but somehow understandable) trend to proceed to making complex items without knowing too much about the basics. Some hobbyists are satisfied with the outcomes of their work (so there is no reason why they should look for improvement); many others face problems and look out for help, not least justly accusing the bad performance of their black powder of being responsible for the outcomes.

Different grades of corned homemade gunpowder, manufactured combining ball milling and CIA

It is the purpose of this page to assist both the newcomer and the experienced hobbyist in discovering suitable methods of small-scale black powder manufacture. It discusses and compares the most relevant methods for home use in terms of efficiency, effort, cost, safety and outcome. With the informations provided everyone should be capable of manufacturing diverse qualities of gunpowder ranging from basic, slow-burning composites (not every application requires a fast product!) to black powder reaching or surpassing the performance of commercial grain.

In addition the Black Powder Manufacture - Questions page tries to answer possible questions and will respond the objections.

Upcoming: Characteristics of good BP

The following table compares some of the most common methods of small-scale BP manufacture.

(*) depending upon the efficiency of your mill (**) watch out for spillage of hot material! Gloves are essential! (***) depending on how carefully the process is executed

About table: Efficiency is determined by the output of the process per unit of time. Effort describes how much work is necessary to produce an amount of powder (the time the pyrotechnician is busy with production; a running ball mill however does not add to this but to the first aspect). Performance compares the burning characteristics of the outcomes (it is plain that for a meaningful comparision we must use the same raw materials in every method).

Mixing screens

A.) Screening prepared materials:

The screen method is the most common method of mixing compositions (e.g. for most stars, fountains, etc.) and consists in passing prepared, hand mixed raw materials through a mixing screen several times. Although via this method the materials are sufficiently integrated for most pyro uses, the same is not true with gunpowder. If we mix gunpowder ingredients using the screen method the outcoming product is very slow burning and leaves a lot of residue. Powders gained by this process are combustible but performing too weakly for realistic use wherever we want to produce force or transfer fire fastly. On the other hand when all that we desire is a cheap combustible product screening is all we will have to do. Such a screened composite is often called "scratch mix" or "green mix" and is the prime of choice for most stars (not for e.g. AP based ones).

Apart from priming, the only popular use for screened black powder in modern pyrotechnics is as a structural filler in (cylinder) shells. As such it is called Pulverone (Polverone) or rough powder. Polverone is BP (with additional binders) integrated using the screen method and processed by wetting and rubbing it through a window screen (a process often referred to as ricing). Many pyros also denominate well-integrated powders that have been riced as polverone, although they are actually using the wrong term. Polverone fills the spaces of e.g. cylindrical comet shells (similar to sawdust) and burns away when the shell goes off; due to its weak burning characteristics it is not used to lift or break shells (except in Maltese shells).

Using the screen method for making BP is highly efficient because it allows producing a high amount of powder in a short period of time, quickly screening the ingredients together. Effort and cost are low. Due to the low friction sensitivity of gunpowder the process is comparably safe. However, the performance of the outcome is very low.

B.) Hand grinding (wet or dry):

Hand grinding different materials using mortar and pestle has been a common mixing method for centuries and is still sometimes used by pharmacists and chemists. Except probably in the laboratories of its inventors and for experimental use, namable quantities BP were never manufactured in this manner - with good reason. Hand grinding gunpowder for some pyros (due to absence of suitable skill or machinery) still is the method of choice but it undoubtedly also is the most laborious method you can choose.

The force of the product will generally rise the longer the materials are ground, but there is a practical limit of fineness and integration approachable via hand grinding. Because of the properties of the grinding action the efficiency of the process will decrease if we increase the amount of material in the mortar (hand grinding needs a special technique and the materials are successfully ground only when we drive the pestle around the walls in a circular manner: too much material present makes efficient grinding impossible). So we can only grind a small amount of material at once. Even when the process is carried out correctly with a heavy pestle, it can take hours until the materials are suitably integrated. The force of the end product however remains weak (compared to other methods) under all practically defensible circumstances. Furthermore there is a small but existing risk of spontaneous ignition due to shock or friction; this and the fact that the pyro is always in close proximity to the powder being integrated makes this method comparably unsafe.

Some pyros argue that wet grinding drastically improves the outcome and makes the process safer, but the former argument remains doubtful. A moisture content imitating the conditions of commercial wheel milling does not add much force to the powder under low pressure hand integration. On the other hand, if we adapt wet methods (as those known for mixing very sensitive compositions) and increase the moisture content up to 30 percent by weight integration may be promoted, but the formation of large crystals of potassium nitrate during a slow drying process will break the performance of the powder.

To sum this up I do not advise anybody to use hand grinding to manufacture BP. However the process itself is easy and no further description is necessary.

C.) Three component milling without a ball mill:

In absence of a ball mill using other mills is standing to reason, e.g. coffee grinders or small scale macerators for kitchen use are cheap and readily available. Such machinery is not designed for continous operation but for an operating time ranging somewhere between a few seconds and minutes. There is also a practical limit for the achievable fineness of grist, so the materials won´t become finer after a certain period of milling.

While such mills are useful items for the preparation of raw materials (e.g. quickly grinding coarse saltpeter for use in stars) or of BP fuels before using the CIA method, employing them for three component BP milling (due to weak integration) only produces a slow burning product. Its performance probably ranges somewhere between screened and hand ground powder.

Depending on the capacity of your machine the efficiency is generally high. You can knock out a viable quanitity of powder in a short period of time, but the method is rather unsafe because a highly combustible composition is exposed to rotating metal blades or similar. Three component milling in small grinders is not advisable both from a safety and performance standpoint.

D.) CIA method without preparing materials (in ball mill): --> see H.)

E.) Three component ball milling (up to three hours):

Ball milling certainly is the most popular method for small-scale BP manufacture and can produce fast powder. Ball mills are capable of grinding and integrating materials down to a degree of fineness only few other mechanical methods can achieve. In pyrotechnics the ball mill method is reserved for two purposes for safety reasons: it serves well for a) the preparation of individual chemicals (e.g. before screening) or the integration of non-combustible compositions, and - with provisions - for b) the dense mixing of gunpowder type compositions without any metals. Ball milling must not be employed for mixing any compositions containing chlorates, perchlorates or metal powders!

When it comes to BP manufacture, we want ball mills to grind and integrate the raw materials as well as possible. But mills are not mills. Many ball mills are capable of producing very fine materials and fast powders in under three hours while other mills need a considerable number of hours to give the same outcome. But why is that and what is a good mill? Many people have done research about what makes a mill efficient, with Lloyd Sponenburgh leading the way. The reason that the mills (also known as Sponenburgh-mills or Sponenmills) designed following his concept are efficient cannot be found in the parts he uses or the ambitious mill layout he proposes, but in the compliance with some basic but very important construction principles. The details are best given on a distinct site concerning ball mills, but the most important points are:

• the jar is correctly proportioned and rotates at the right speed for its size

• the size of the media conforms to the jar size

• the amount of media stands in correct relationship to the jar capacity (50% of volume)

• the amount of processed material (load) stands in correct relationship to the jar capacity (25% of volume)

Using an efficient mill drastically reduces the milling times because every strike of the balls actually crushes material; milling times exceeding the three hours will not be necessary and will just unnecessarily wear both jar and media. Also note that in case of ball milling there is a practical limit of achievable fineness, so after a certain period of grinding the material will not come out noticeably finer or better, even if you grind it for weeks.

Now how is milling done? Once you determined the optimum charge for your mill, basically all you have to do is to load and switch on the mill. The tables give a description of the process.

What does determining the optimum charge mean and why do I have to do this? The opinions differ on how to best determine the optimum charge but I'd like to keep things easy and use the following method: The main problem is that ball mills are loaded by volume but we want to measure our raw materials by weight (with a scale). In other words, each time we load the mill we want an easily and accurately measurable (weighable) amount of material corresponding to both the optimum charge (by volume) of our jar and the ingredient ratios of the BP formula. Given these requirements we can´t just weight out a pound of raw materials and charge the mill by taking out a volume measured part equaling the optimum charge, because the ingredient ratios of this part taken out of unprocessed material will most likely deviate a lot from 75:15:10.

Proceed like this instead: If you use your new jar/mill for the first time weight out enough raw materials to give a pound of black powder and process them by hand as well as you can (e.g. by grinding them separately in coffee grinders and integrating them with screens) to produce a pound of fine green mix. Then measure a volume of green mix equaling the optimum charge of your jar (25% of its empty capacity) and weight it. This weight value is a close approximation of the weight of your mills optimum charge; let´s say it weights 150 grams. That means each time you´re going to mill BP in the future the only thing you have to do is to weight out 112.5 grams of bulk KNO3, 22.5 grams of bulk charcoal and 15 grams of bulk sulphur. You can optimize these specifications by measuring the outcome volumes of milling processes and accounting for deviations the next time. Note that you most likely will have to alter your optimum charge weight when using different kinds of charcoal (they largely deviate from each other in volume).

Due to the necessary milling of potassium nitrate three component milling is probably the most inefficient way of using your mills capacity for BP manufacture. Unless you are using large or multiple jars the amount of powder that can be processed at one go will be much less than you think it´s gonna be (note that the optimum charge is only 25% by volume of the empty jars capacity and especially charcoal is very voluminous, taking up a lot of volume and decreasing the possible charge weight).

The manufacturing process is quite effortless for the pyro because his mill does the majority of the work. However, three component milling of BP materials exposes a potentially inflammable substance to high amounts of shock and friction, although BP is known to be comparably safe in relation to other pyrotechnic compositions and ball mills employ parts (non-sparking grinding media, jars etc.) that drastically reduce the chance of accidental ignition, mills loaded with BP have been known to explode - with devastating results. I don´t want to convey the impression that three component milling inevitably ends in an accident (hundreds of pyros do this daily - and still are alive), but I (and many others) dislike milling a highly energetic mix in a confined space with heavy balls potentially acting as shrapnel. Speaking of possible hazards, hard (often metallic) foreign matter possibly contained in your charcoal and/or potassium nitrate pose a risk. To sum up, I would avoid three component milling, especially if alternative methods giving equal or better results are available. Such methods - against common sense - do exist and will be explained here.

F.) Three component ball milling (for more than three hours)

The process is the same as in the case of E.) but the mill is left running for a longer time. With regard to the pyro community numerous enthusiasts of ball milling can be found; they agree in their opinion on milling and vote for long milling times, sometimes ridiculously long such as overnight, a day, 60 hours and more.

While excessive milling may be necessary when using a mill of very low efficience, let me briefly mention some arguments against such practice:

• there is a practical limit of achievable fineness, so super-long milling will not much improve the outcome

• excessive milling wears media, jar and motor and consumes energy wastefully

• there is no need for excessive milling when using an efficient mill

• a running mill poses a potential hazard

Don´t get it wrong: if you are successfully using this method and are willing to accept its drawbacks, there is no reason why you shouldn´t persist on it. I´m just giving some arguments here.

G.) Double & double component ball milling:

The potential dangers of three component milling can be avoided by using double and double component milling. The idea is to use two seperate steps of ball milling and to integrate the results by non-milling means (e.g. by screening). In this case the possible performance gain of milling the oxidizer together with a fuel is still taken into account but the oxidizer-fuel ratio is modified in a way producing a non-combustible compound. While milling compounds showing mixing ratios of potassium nitrate to charcoal varying between 4:1 and 6:1 (also called the critical proportions) in actual fact is still as dangerous as three component milling, the oxidizer-fuel mix becomes incombustible when we raise the proportions to 15:1.

Against this background double and double component milling involves milling all of the potassium nitrate mixed with one third of the charcoal in a first step, and milling all of the sulphur together with the rest of the charcoal (again incombustible) in a second step. The outcomes of the two milling processes are finally integrated without using a ball mill.

The efficiency of this method is lower than that of three component milling because two milling steps are necessary. However the process itself is much safer and the powder produced can be just as good.

H.) Combined ball milling and CIA

The CIA Method

Against one´s expectations the CIA method has nothing to do with the well-known US secret agency. Although similar techniques had been investigated by others earlier, the method presented here is the result of a series of studies conducted in the environment of the US army during the 1960s. The results of the study on black powder were published in a booklet entitled "CIA Field Expedient Preparation of Black Powders"; the booklet contained experimental data along with a how-to on improvised gunpowder manufacture addressing to US army soldiers in the field.

The method makes use of the fact that potassium nitrate is incredibly soluble in water. When a substance is dissolved, its "particles" are separated from each other on a molecular level - a property not attainable by any mechanical means. Thus, when we dissolve potassium nitrate, this implies: a.) the particles of the nitrate become very small, and b.) nitrate can be soaked into the pores of the charcoal, ensuring an intimate integration - two essential advantages when it comes to fast powder. However, the question is how a solid material can be retrieved from a solution without forfeiting the advantages only just obtained? When we allow the liquids to evaporate slowly, large crystals of KNO3 are formed, preventing the dried powder from reacting quickly.

On the other hand, when we use alcohol to precipitate the dissolved nitrate, its particles remain small and the resulting powder does not loose its explosive nature. This comes from the fact that potassium nitrate is insoluble in a water/alcohol mixture, while the alcohol also acts as a dehydrating agent and absorbs part of the water.

However, although the CIA booklet contained some valuable information, the outcomes of the method belied the high hopes of many pyros who had ordered both the booklet and lots of alcohol. The resulting gunpowder could not reach the performance of commercial. But why? While the original CIA approach requires optimization to give the best results possible, the inferior performance of many precipitated powders is explained mainly by an insufficient integration of the basic materials, in this special case, charcoal and sulphur.

Improving the CIA approach

Those of you who have ever tried to grow crystals will probably be aware of the following: If you want your crystals to grow large, you will have to allow your salt saturated solution to evaporate and cool down slowly. Conversely, we can employ this factor to our advantage when we rapidly cool down a saturated solution of potassium nitrate. Doing so will end in tiny (invisible) crystals and thus an improved integration of KNO3. Given these requirements we will concentrate our attention on the alcohol, which both absorbs the solvent and cools down the mixture, and improve the method by:

• using more alcohol
• using colder alcohol.

Although using more alcohol will raise the production costs of your homemade powder, it will drastically improve its performance. It´s a good idea to be generous in case of alcohol. Generally it is desirable to cool down the alcohol as far as possible; put it in the coldest corner of your refrigator (don´t use glass containers!) and leave it there for several days. Alcohol remains liquid far beyond the freezing point of water. It will take a considerable amount of time to cool it down properly.

Improved CIA without ball milling

When we make use of an improved CIA method and proper raw materials, we can produce a suitable black powder product even in absence of a ball mill. Although its burning speed is nowhere near commercial, it´s good enough for many pyro applications (for lifting stars, comets, shells, making fuses etc.). The CIA method is the best choice for those of you who don´t have access to a ball mill. In this case a coffee grinder or a small kitchen macerator is used to reduce a combination of charcoal and sulphur to a fine powder. The premixed C/S is then employed in the CIA process described below.

Combining improved CIA and ball milling

When the advantages of both CIA and ball milling are combined to manufacture black powder, the performance of the end product can reach or surpass commercial. While the CIA method - if properly executed - ensures a superior integration of potassium nitrate, the ball mill method is employed to intimately mix charcoal and sulphur.

I personally consider the combined approach to be the best method for amateur black powder manufacture (I attempted to argue why I rate it higher than plain ball milling). Even in case of comparably short milling times the resulting product is more than fast enough for all kinds of pyro use. On the other hand, if we desire further improvement, we can simply change this variable and mill the C/S for a longer time.

However, to give the best possible outcome the whole process - especially the wet mixing and precipitation procedure - has do be supervised and executed with great care and precision. The following lines try to give a detailed description of the process and point to possible problems.

SECTION UNDER CONSTRUCTION - Do not try out until method has been described in detail!

Recommended literature on BP (examples):

Lancaster, Ronald: Fireworks. Principles and Practice, 3rd edition, Chapter 3: Gunpowder

Sponenburgh, Lloyd: Ball milling theory and practice

Von Maltitz, Ian: Black Powder Manufacture. Testing and Optimizing

Von Maltitz, Ian: Black Powder Manufacture. Methods and Techniques

UPCOMING:

Post processing

Testing and Storing