Create a life-size template of the artwork you plan to paint, by drawing it as a sketch on drawing paper or butcher paper.
Plan to paint only as much as you feel you can accomplish in one sitting. Measure the area you plan to paint, and mix a batch of plaster based on your measurements.
Measure one part slaked lime to two parts sand. Mix in water slowly until a smooth paste develops.
Create the arriccio layer of your painting by applying the plaster mixture with at trowel to the area you will paint. Allow the layer to dry for at least two days until it turns to calcium carbonate.
Mix pigments in your choice of colors with distilled water. Prepare all your color choices before applying the final layer of plaster.
Make an intonaco mixture by combining equal amounts of sand and slaked plaster. Add water into the mixture until the paste is thick.
Apply the intonaco mixture to the arriccio layer with a trowel after completely wetting the arriccio layer. Smooth the intonaco layer down with a spatula.
Test the painting surface by brushing water onto it with a paint brush. The painting surface is ready to accept paint when water absorbs quickly on contact.
Arrange your template on the moist plaster surface.
Apply layers of diluted paint to build up the colors you are working with, until they are as bold as you want them, and visible from a distance. Apply lighter colors over darker colors.
Allow the painting to dry and set for three weeks. Re-paint as necessary to achieve the look you want, if necessary.