Hi, I'm going to show you how to make firecrackers out of innofensive sparklers. First of all, I'M NOT RESPONSIBLE OF ANY INJURIES THAT THE CONSTRUCTION OR USE OF THIS THING COULD CAUSE. THIS IS DANGEROUS AND IT SHOULDN'T BE ATTEMPTED BY IRRESPONSIBLE PEOPLE, OR INJURIES LIKE BURNS COULD HAPPEN. Second, sorry for bad english, I'm spanish. So, after this warning, let's start.
Step 1: Collecting the Sparkler Compound
Ok, so first of all you need a sparkler. You can acquire them in lots of places, ranging from the cheap chinese store to the specialized pyrothecnics store. Normally you can buy a pack from a few dollars and one sparkler stick is enough for a firecracker, so in my case, I bought 12 packets with 10 units each so I got 120 sparklers for only 7$. Not bad. Now that you have the sparklers, you need to take their compound. you can use pliers, but it's dangerous, as sparks could ignite the compound easily, so I prefer to use my fingers that ended covered in grey compound :D.
NOTE: I used pliers here because I didn't realize how dangerous it was. Please be careful
INTERESTING FACT: This compound is made with: aluminium, magnesium, iron or titanium as metallic fuel, sulfur or charcoal as extra fuel, Potassium nitrate, Barium nitrate, Strontium nitrate or Potassium perchlorate as oxidizer, chlorides and nitrates of metals in the colored sparklers and for holding everything together, dextrin or nitrocellulose. this is from wikipedia http://en.wikipedia.org/wiki/Sparkler
Step 2: Grinding It to Powder
Now you need to reduce the big bits to powder. I used the bottom part of a screwdriver here, because it's round and most important, It's made of plastic. I used a cardboard box also. NEVER USE METAL AS SPARKS COULD IGNITE THE POWDER!!!
You'll need to grind it untill you see a really fine powder
TIP: use slow and circular movements to grind the compound and apply a bit of pressure.
Step 3: Filling the Firecrackers
Ok, so now you need something to put the compound in. In this case, I used the 9v battery inside batteries. they work well but they are a bit dangerous as they are made of metal. I prefer to use them for the "rocket" variant of this experiment (will explain that later). So for safety, I now use hand rolled cardboard tubes. I will make a separate instructable of how to get the metal tubes or make the carboard tubes. You can compress it or not, depends on what you want this device to do. If you want a high teperature flame ("rocket" thing) don't compress it. If you want a loud explosion, then compress it. Don't fill it to the top, as you'll need some space for the fuse and the strars
Step 4: Personalizing It
Now you can add pyrotechnic stars or chemicals for making the flame go red, blue or green or make the explosion leave trails and cracklings of different colors. I found mine in the floor after a firework show. They are like little black things, sometimes spherical, sometimes cubic or amorphous. You know when it's a star when you watch closely and you see that is made of compressed gunpowder, glittering with light. I don't know what color are these stars going to be, as I picked them randomly from the floor, so it's always a colorful surprise when you see them burst into colors
Step 5: Adding the Fuse
put the fuse inside the compound and now fill the rest with the compound, leaving a small gap for closing it. In my case, I used visco fuse, as I have lots of it from failed/broken/dangerous short fused firecrakers, but you can use any fuse you want, like monetti or bickford fuses. You can buy them here: http://www.pyrogate.eu/safety-fuses/ or in the closest pyrotechnics store
Step 6: Closing It
Now you need to close your firecracker. For explosions: Here, I used hot glue. I don't use the gun just because I like to heat it untill it becomes liquid, so it makes a better seal. I use a jet lighter for heating the bar and then I fill the gap. Let it dry for at least one minute
For flames: the same than the other step, but you need to make a little hole in the glue, so the combustion gases can go out and produce a fiery flame that will make the metal tube to glow red hot.
Step 7: Finished
Hope you enjoyed this instructable. Please comment, share and be safe. Have fun!