Unglazed ceramics may either be glazed and then fired, or painted and not fired. If you are going to glaze your ceramics, note that the end result after firing will be much different than the piece before firing. You will need to have access to a kiln, and you will wish to consult with an expert to find the right glazes for your set.
If you are painting and not glazing, acrylics and oil paints are the most appropriate choices. Acrylics dry quickly, and thus it is more difficult to blend acrylics than it is to blend oil paints. Oil paints, on the other hand, dry very slowly and are easy to blend. Oil paints must be carefully stored while they are drying. The choice between acrylic and oil is purely a matter of preference.
Take time to work on the flesh tones of each individual in the scene. Realistic flesh tones are most commonly made from reds, yellows, browns, whites and blues. Experiment with the colors until you are satisfied with the results. Lighter skin tones will have more reds, yellows and whites, while darker skin tones will be made from browns, reds, yellows and blues. Vary the flesh tones slightly from one face to another to add to the realism of the final product.
Study different nativity sets before beginning your own. Often the three kings will be painted in bolder, more decorative colors than the other figures. Mary is frequently clad in blue and red, while Joseph may be wearing dark brown or green. The angel is most often dressed in white, while Jesus is often shown bundled in white.
Make a plan before beginning to paint. Know which colors each figure will be. Select earthy colors such as browns, rusty reds, ochres and mellow blues. To make a set that is visually cohesive, pick a palette of limited colors and stick to that palette for each piece of the set.
First lay down the basic colors on each piece of the nativity. Next, with a thinner brush, focus on the details. Paint over any mistakes, giving the nativity time to dry between layers.
To emphasize the humble nature of the surroundings, add touches of dust to the clothing of Mary and Joseph, and on the animals. This is done with a light layer of sandy brown or reddish brown, applied around the feet or knees of the figures. The layer should be transparent and discrete. The three kings will be bearing beautiful gifts.
After you have painted each figure and let them dry, set up the nativity where you plan to keep it and step back from the scene. Do the figures match each other? Is there anything that stands out? Make changes as necessary.