Glue each of the 12 layers together (into 'bowl' shapes) and then lay them out in a large cardboard box. Take this outside to spray. Shake the black aerosol can extremely well for up to 3 minutes to make sure that it is thoroughly mixed. We find it helps to put suitable music on whilst shaking the aerosol can!!!
Spray approx 8 inches away from the 12 tree parts gently moving from side to side and moving from one end of the box to the other until all of the parts are completely covered in black paint. Leave to dry for about half an hour. (They should actually be dry enough to touch in about 15 minutes). You can turn the parts over and spray the underneath repeating the instructions if you want the underneath covered. There is enough spray in the can to cover 5 trees if spraying both sides or 10 trees if spraying one side.
When dry, pour a small amount of clear PVA glue into a saucer and pour the iridescent glitter into a separate plastic container. Using a small piece of sponge, dip this into the PVA glue and then gently dab it over one of the black painted tree layers until you have covered all of the black paint. (You may do a bit of the layer at a time which will prevent the glue drying out before you apply the glitter). As soon as the glue has been applied, dip the layer into the iridescent glitter making sure that all of the glue/black paint is covered. You can make use of a small paint brush to help apply the glitter. Lift out of the glitter and thoroughly shake off the excess back into the tray and you will be amazed at the result. Repeat for each of the 12 layers and let them dry thoroughly before continuing to assemble.