Place the cake on a swivel base that slides very well. With a large spatula cover the cake with a layer of bitumen, trying not to touch the bread directly, but touching bitumen with bitumen, to avoid removing the crumbs.
Smooth the bitumen with the spatula keeping it at a 45 ° angle towards the cake and making a continuous movement of the rotating base. Be careful to always clean your spatula.
Divide the rest of the bitumen in three bowls and paint with the vegetable dye in three shades of color starting from the lightest to the strongest.
Place the duyas inside the sleeves, cutting the ends so that they fit well.
Fill the sleeves with each bitumen and you have pressure to lower the content. Roll the sleeve so that the bitumen does not come out when it is time to use it.
Start decorating the cake with the strongest pitch of bitumen, placing your hand horizontally on the cake and placing the broad part of the duya stuck to the bitumen so that it sticks.
Make top-down movements to make the waves. If you are wrong you can remove the decoration with the help of a toothpick.
Continue decorating by making waves with the rest of the colors, until the cake is completely finished.