To take the mixture further with more tints, just mix your custom colors with the next darkest or lighest tint and make an in-between custom color. This photograph is showing the all the color tints that have been made. Now it is time to make them into the shapes and sizes that you want. Lay them on absorbent paper until some of the moisture has been absorbed then move to wrinkled plastic wrap to dry. Store your new custom pastels in boxes that are lined with foam, or use premade boxes that you can buy from art supply houses.
Photograph is of finished pastels made in various shapes for various techniques.
I tend to like the triangle shape that I have learned to make. It gives me edges that I like and also fits in my fingers well. Note that the pastels are drying on a wrinkled plastic sack. When the pastels have completely dryed, they will be slightly lighter in color than they are when they are wet. Deb, llis, and Carly Learning to make pastels was fun.