Start by applying a thin layer of acrylic molding paste (as I did) or gel to your surface with a plate knife. Smooth the surface as evenly as possible.
Then gently drag a comb through the wet paste from side to side. Wipe off the excess paste with each swipe of the "comb". Then repeat making vertical lines. Be careful to use a light touch with the "comb" or you will erase the horizontal lines as I did here.
I used indigo Lumiere paint for the first layer to completely cover the paste. Then erratically brushed on some turquoise Lumiere paint and created a light shimmery purple to brush on by mixing d. purple and pearl white Lumiere paint.