Screen method
From PyroGuide
Screen method - is a way of mixing pyrotechnic compositions using a screen. It should be noted that this method should only be used for compositions that are not friction or shock sensitive, for example flash powder and whistle mix should not be screened. They should be mixed using the diaper method.
Place the composition into the screen and sieve the contents into a bowl or paper sheet. If there are any clumps remaining push them though with a wooden spoon or non-sparking tool. Continue to run the composition through the sieve until you obtain a homogeneous mixture.
This is a fast and easy way to mix an insensitive composition like black powder.
Measure all chemicals using a scale. It is commonly suggested that fuels and oxidizers should not be screened together. Some compositions can be screened together, but following the common guidelines should keep you safe from harm. The components in this picture make up one kilo of a metallic fueled red star composition. Once you have the right amount of each chemical weighted out, you can prepare for the screening.
A screening station could look like this. For larger batches, I prefer to use a tub formed box as liner to keep the screened compositions from spreading around. The mixing sheet is a piece of sturdy transparent plastic, which isn't very sensitive to tare or puncture. Screening can create significant amounts of dust depending on the composition. Therefor, it should be done outside wearing a respirator with small particle -certified filters.
Step three
The process itself is very straight forward. As you migh guess, the goal is to render large chunks of chemicals into smaller, mixing the composition at the same time. A fast side to side motion works on finely divided particles, but you might need to work larger and tougher particles by hand to render them into a passeable form. When all of your composition has passed the screen for the first time, you will have a non-homogenous mixture on the sheet. You can continue the mixing by either diapering the mixture, lifting the opposite corners of the sheet repeatedly, or as I prefer, repeat the screening process a few times for a very homgenous mixture.
