Or place the foil over a stencil, again using your hand to rub the foil into the stencil, placing the stencil over paper towel or newsprint, helps get a good impression.
The authors didn't mention using an embossing stencil, but this also gives a good impression. You can either rub the foil with your hand or run through a Cuttlebug or other embossing machine.
Next, use a palette knife to spread gel medium on the surface you are "treating", then place the foil over the gel medium and GENTLY press the foil into the gel medium to adhere (you want to avoid rubbing out the impression you made).
Use a paintbrush to paint with acrylic or other paints. Let dry before proceeding with art.
On this one, I used two layers of q. nickel azo gold and n. red light:
On the tree stencil one I used q. nickel azo gold and n. red light, when the paint dried I sanded the surface.
Here's the result:
On the one done in the embossing folder I used q. nickel azo gold and d. purple:
Another technique in the book to create texture with aluminum foil is to place a thick layer of gel medium over your surface, lay down the foil, press in. While the gel medium is still wet, run a comb or texture tool over the surface. Allow to dry before painting.
This one was also painted with q. nickel azo gold, n. red light and q. magenta:
Other techniques mentioned in the book are printing an image on vellum and adhere to the foil; printing an image on gampi paper and adhering with spray adhesive; creating a glue crackle on the surface; adding a thin layer of clear gesso and drawing over the surface and gluing objects under the foil to create prominent shapes. This is a book worth having in your collection!