Lift charge
From PyroGuide
In fireworks, a lifting charge is an amount of energetic pyrotechnic substance which is placed under an aerial shell, comet, star etc. to propell and lift it into the air. Black powder is employed for this purpose. It is not used in powder form, but as granules to provide a high amount of force in a short period of time. Corning and ricing are two common techniques to granulate black powder for use as a lifting charge.
Ricing
Start by mixing 3-5% dextrin in your meal powder and slightly wetting the mixture. Push it through a metal sifter to create larger grains of lift powder. The powder from the granulation should be as close to grains as possible, if the powder is string-like you have added too much water. However if the powder does not form grains you have added too little water.
Corning
Take your meal powder and wet the composition with roughly 5% of it's weight with water. Mix thoroughly and place into a die and compress with a hydraulic press until you form a solid cake. The idea is to give the black powder a density of 1.7 g/cc. Allow this to dry in the sun for a few days. Next you need to take the cake and break it up in a mortar and pestle or similar. This can be a dangerous operation and should be done in small amounts. You should use a full face shield, hair cover and heavy gloves. You can then screen by particle size into different sized categories for your intended purpose.
[edit] Amount of lift powder?
The only real way to find out how much of a certain kind of lift powder should be used, is to make a dummy shell having the same weight, size and shape as the shell being launched. Then the amount is upped or downed by trial and error. However, as a starting point, a rule of thumb is to use one ounce of 2FA black powder for every pound of shell weight up to 10 lbs, and 1/2 oz of lift for each pound in excess of 10 lbs. The larger the shell is, the more factors such as mortar length, shell length and shell clearance come into play. If a shell is light compared to the size (like a patern shell where fewer stars are used), a larger amount of lift should be used, and thus the rule of thumb will not apply for this type of shell.
For small shells, like those under 3", the generally accepted amount of lift powder is 1/10 the weight of the aerial shell being fired. For example, a 60 gram shell would require 6 grams of lift powder. If you want more altitude on your shell, simply add a little more lift powder, but be sure not to add too much... Too much would most likely end with a flowerpot...
