4. Cover the entire surface with gesso to seal the shapes
Gesso is an art supply used as surface preparation or primer for painting, gilding, and sculpting. Its origins are uncertain, but gesso is believed to have been developed in Italy, since the word gesso is Italian for 'chalk'. Preparation varies according to intended use, but usually consists of mixing glue with plaster, chalk, or gypsum.
Gesso resembles paint, but is thinner and dries hard. Gesso is applied with a brush and must dry before the surface can be painted. It was first created for use in painting, in order to give the surface the right properties to receive paint. In Gothic and Renaissance panel painting, gesso was applied over a panel of wood in order to give the paint something to adhere to. It created a slightly rough surface and prevented the paint from seeping into the wood.