First, I selected some 100% cotton string, a piece of white paper towel, and some cotton balls as my sources of cellulose. I very carefully made a 2:1 volume mixture of concentrated sulfuric and nitric acid in a small glass beaker. After stirring gently, I placed this beaker in a bucket of snow to cool the nitration. I nitrated my three sources of cotton separately, one after the other. To nitrate each batch, I placed it in the acid mixture for 15 minutes. After the time was up, I transferred the now-nitrocellulose to a saturated baking soda solution to neutralize remaining acid. Finally, I thoroughly washed the nitrocellulose with plain water and let it dry.
One interesting thing I noticed was that the cotton balls almost seemed to freeze in the mixture. It was quite cold when I did the experiment, but the stiffening could also have been caused by close packing. I had just enough acid to cover three cotton balls at a time, so they were squished.
The homemade nitrocellulose is quite inflammable. I have even held pieces in my hand and lit them without hurting myself. While the paper towel and the cotton seem to burn extremely quickly without any residue, the string burns slower and leaves some charred material behind. A cotton ball that I nitrated at the end of the run also left some residue--perhaps the acid was nearly used up. The best cotton burns so quickly that it can detonate under the right conditions.
I put the device in a cardboard box with a polycarbonate viewing window and set it off from another room using my flash capacitor bank. I was wearing hearing protection (a must for explosions), but from family member accounts, the ensuing explosion was frighteningly loud. The shell casing was completely blown to pieces, with brass shrapnel flying through the cardboard box and also embedding itself a centimeter into a nearby block of wood. I was quite impressed by the detonation-it was much more powerful than I had expected.
If you read the preceding two paragraphs, please don't do anything stupid. While exploding bridgewire detonators are incredibly safe (as they contain no primary explosives), shrapnel is much more dangerous than a simple fireball. If you repeat this experiment, make sure you will be protected from potential shrapnel.