There don't seem to be any text files out there that discuss casings or processing, though I've personally downloaded hundreds that contain formulas for pyrotechnic mixtures. Now we can change all that.
So what's the big deal about casings? Just a paper tube, right? No, not quite. A roman candle casing has to be able to handle repeated bursts so as to fire its stars like a rifle does bullets. But if all the burning materials inside change the inside diameter of the casing by too much, then the puffs of gas that fire the stars into the air will escape around them and not push them very high. Some of my early attempts didn't fire the stars out at all. A skyrocket casing has to be light, strong enough not to burst even though the pressures inside can be tremendous, and if it has a nozzle it has to grip it tightly enough that it doesn't get blown out of the casing. A firecracker on the other hand, has to be flimsy enough to burst yet strong enough to grip its end plugs rather than let them rip loose and fire off of the end of the casing. There are dozens of other examples, and if the casings aren't built right then you've just built a dud.
So, learning all about various papers and glues isn't nearly as sexy as playing with chemicals, but until you do you may as well just go lighting up little piles of powder. You'll save a lot of money, and the results will be no less spectacular. But there's a lot more to this than we can cover in the size text file that's been typical of this series. We'll break this topic up into a group of files that are a bit larger than usual. This will just be part 1 of the discussion on casings and construction.
So, now that I've shamed you into wanting to learn about paper and glue, let's get down to business. There are two kinds of paper tubes available. These are called spiral wound and parallel wound. If you've ever tried to wrap a sheet of paper around a dowel, pencil, or broomstick handle, you produced a crude parallel wound casing. We'll be sharpening our skills in this area. Spiral wound casings are made by wrapping thin strips around a round dowel form in a spiral pattern. Tubes used to hold wrapping paper, paper towels and toilet paper are made using this method, so check one of these if you have trouble picturing the method. Spiral wound casings are almost useless in fireworks as they have much less strength. Only firecrackers like M-80s use spiral wound casings, and that's because they're not supposed to be strong. So if you happen to come across some spiral wound tubes that are the right size to cut up for M-80s, you may be able to use them. Otherwise, they're probably not all that useful, even if they seem thick enough.
Just so as not to worry anybody, you don't NEED a spiral wound tube for M-80s. A suitably thin parallel wound tube will do the job just fine. Spiral wound tubes are frequently used wherever possible because they're cheaper to make. Machines that handle thin strips of paper don't make as many wrinkled tubes as machines that have to handle wide sheets. Since we'll be doing our work by hand, this need not bother us.
The good news here is that the materials won't be nearly as hard to come by as some of the pyrotechnic mixtures mentioned in earlier installments. There are different types of glue formulas, most being variations of flour paste, which you can select, depending on what's convenient to you. If you don't feel like doing the slimy work needed to make this muck, I'll mention that I've had some success with commercial white glues, like Elmer's Glue All, though this tends to make a casing that doesn't accept certain types of end plugs very tightly. I wouldn't use it for rocket casings, and firecrackers have to be specially constructed. It's also going to cost a lot more than flour paste. You can experiment with it for small batches, if you like. It's also possible to get passable results with batches of white school paste, thinned down with enough water to make it flow. But if you're going to make a reasonable number of casings, you'll need larger batches of glue, and you can make it fairly cheaply and simply.
A good, homemade glue that will make strong casings is made by adding 4 1/2 cups of flour to 3 cups of boiling water and then adding 1/8 ounce of alum (aluminum potassium sulfate). Stir this combination until it is consistent in blend. When it's cooled, it's ready to use. The flour is the actual glue. The alum helps fireproof the mess and helps act as a preservative. This is important, as wet flour will eventually spoil, and so this mess has to be used up fairly quickly. Don't count on saving it for more than a couple of days and especially don't try storing it in a jar or other closed space. The flour will spoil by fermenting, producing lots of gas, bursting your jar.
But if spoilage is a real problem, can we let the flour spoil BEFORE we make the glue? This is not as silly a question as it sounds. By doing this, we make a slop that can be kept a month or so, if it's also kept in a reasonably cool, dark place. Just don't make it on a full stomach.
Pour anywhere from a few cups to a few bucketfulls of flour into a container large enough to cover it with a good layer of water but still be only a third full. How much water you use doesn't matter too much right now, as most of it will be poured out later. Just make sure that you're making a batter, instead of a dough. Stir it up good, but don't worry too much about little lumps. That will be corrected later.
Now for the revolting part. Let the stuff sit for 2-3 days in a warm (90 degrees F) place and check it after then. If it hasn't begun fermenting by then, drop in a few pinches of instant yeast. When the fermentation is finished and there are no more bubbles forming, the flour will have settled as a gooey layer at the bottom of a pool of revolting brownish liquid. Get rid of the brown slop and note how much batter is resting in the bottom of the container. Boil enough water so as to have a volume that's twice the size of the batter, and pour it in slowly, stirring the flour briskly. It'll start out being easy to stir, but will get thick in a hurry. If you're only making a few cups at a time, it won't be heavy enough to hold still while you're trying to stir it, so you might want to have the container clamped down solid.
If you did it all right, you should have a batch of clear, smooth paste that's plenty sticky and fine for sticking your casings together. Since it's already a spoiled batch of flour, it can't go bad a second time and needs no preservatives.
If you plan to use any Chlorates in your fireworks you should also add some potassium carbonate dissolved in water to your glue before using it to make any casings. I always put it in, no matter what I plan to do. The reason for this is that glue tends to deteriorate slightly, producing a slightly acidic material. Old paper used in the casings can also become acidic. Any Chlorate that comes in contact with an acid will produce tiny amounts of Chloric Acid, which can ignite if you do anything more vigorous than just thinking about it. Potassium Carbonate will counteract the effect of any acids, making your final masterpiece much safer than it would be otherwise. After that, it's still common practice to design fireworks so that no Chlorate bearing portions actually touch any glue.
A super hard pyrotechnic cement can be made by mixing finely powdered Calcium Carbonate (powdered chalk) with Sodium Silicate solution. The proportions will vary depending on the amount of water in the Sodium Silicate, but you can make a few small test batches to check what works best for your materials. The Sodium Silicate should be thick enough to remind you of maple syrup, and can either be thinned with distilled water or allowed to thicken by evaporation, as needed. Stir in the Calcium Carbonate until you've got a thick, sticky mess. When this stuff hardens, you won't be able to clean it off of your utensils, so use items that you won't mind throwing away.
This material makes nice end plugs in large firecrackers, and can be mixed with sawdust and a bit of red powdered tempra paint to make that nice, solid shell that coats cherry bombs. But this stuff is rock hard and turns into a shower of skin and eye piercing shrapnel once it bursts. Keep this in mind as you design your little gems.
This is one of those very important skills that always seem to be ignored in files that describe the pyrotechnic arts. Yet, the properly built casing will make the difference between sucess and failure of your creations. For most casings, brown Kraft paper will work very well. Everyone who's in any way involved with modern civilization is familiar with this stuff as the brown paper bags used by supermarkets, hardware stores, and many other businesses. It's tough and will absorb the glue, making a tough casing. While stores in many areas are switching to plastic bags, it should be possible to save enough bags to meet your needs. If not, you can buy the paper in large rolls from paper supply houses. While it comes in various thicknesses, choose something that's comparable to the paper bags, which seem to be well suited for our needs.
While the simplest casings are just made by rolling a piece of paper over a rod, and then sliding it off and gluing the end closed, these are not of very much use. Most casings need to have glue between the layers of paper to make them hard, have to be cut to the proper length while they're still wet and mushy from the glue, and you have to use care not to glue the casing to the rod you're winding it on.
You have two choices as to the type of rod to use to roll your casings. A metal bar will last longest, won't swelll from the moisture in the glue, and won't easily stick to a stray glue droplet, but is more expensive, takes more work to cut to size, and will quickly dull the knife blade that will be used to cut the casing. A wooden dowel is cheap, easy to cut to length, available in a wide variety of sizes. It will also have to be replaced more frequently if you cut your casings while they're on it, because the knife blade will quickly cut deep grooves into the wood. It also requires extra care to keep from gluing the casing to it. We'll describe the procedure for wrapping a casing around a wooden dowel. If you choose to use a metal rod, you can ignore the extra cautions that using wood will require.
Start with a sheet of paper. One dimension will be about an inch and a half larger than the length of your casing. The other dimension will have to be learned from trial and error, and will have to do with how thick you want the casing wall to be. Wrap one and a half turns of the paper around the dowel and give the dowel a twist so that the paper is wrapped tightly with no slack or wrinkles. Unwrap about a quarter turn, enough so that it still remains tightly wrapped but just barely so. Next, put glue on the paper near the crack where the wrapped portion meets loose portion and start wrapping the paper by rolling the dowel over a flat surface. If you're using a bottle of white glue for this, the long line of glue will glob up and travel along as you roll the casing.
Whenever an area runs low on glue, squirt some more in the depleted area. If you're using a liquid paste, you'll instead want to apply it with a brush. In either case, don't let the glue get any closer than a half inch from the ends of the tube. This is particularly important if you're using a wooden dowel, as any glue that runs out the end will make it difficult or impossible to remove the casing. Keep rolling and applying glue until the paper is all used up. If your casing isn't thick enough, it's easy to fix. Just glue on another piece, keep applying the glue, and keep rolling.
Once you're done rolling, take a sharp knife and place it about 3/4 of an inch from one end, at right angles to the tube. Press down and roll back and forth, and you'll cut away the unglued end of the tube, along with a little of the glued portion. Slide the piece off and do the same to the other side. With a little practice, you can make the knife cut go around in a perfect circle rather than a slightly ragged spiral, and the end of the casing will be smooth. As quickly as you can, slide the tube off of the rod, and set it aside to dry. Besides the danger of gluing the tube to the rod, there is also the problem that the tube will shrink slightly as it dries, so don't leave it on the rod any longer than you have to.
There are a few things to think about; the wetness in the glue will quickly dull the knife blade. Wipe it off immediately after cutting an end. It's not a bad idea to use an X-Acto knife, which uses cheap, disposable blades. You may also find that a whetstone is useful in extending the life of your blades. Another thing to consider is that even if no glue touches your dowel, it will still absorb traces of moisture and after you've wound a couple of casings, it will be much easier for you to accidentally glue the casing to the dowel. It's a good idea to have several dowels and use them in rotation so that each has time to dry off before it gets used again.
After you've had some practice rolling casings, you'll find it fairly easy to roll your casings on one dowel, slide it off before you cut off the unglued ends, slide the end onto a second dowel that's been sanded down to make it just a bit smaller, and use that to cut the ends off. This way, you won't cut knife marks into your good rolling dowels, and when the ends of your cutting dowels get too ragged you can just cut them off and use the fresh end for cutting. You needn't put the cutting dowel more than an inch into the casing before cutting it. This will reduce the chances of getting it stuck.
