IMHO: many things around the house can be used as a stamp pad for interesting texture.
when I need skin cells on something I use a stamp pad I made by pour some latex on a navel orange. then letting it dry, when dry peel off and use as a stamp pad. You can use this the same way with what you are doing with you Mache' Look around the house a see what will make interesting textures on Morti

BTW: He is Great Love him