Traditionally, the base material for runes doesn't have to be solid, just appropriate to the spell. There are some which are carved into ice or drawn in air, and yes, also on paper or parchment. But like the Ogham letters with which I am more familiar, most runes are intended to be carved into, or painted onto, something more substantial. Healing runes, for example, could be carved into a slip of birchwood and either placed in the hand or under the pillow of the sick person, or carved directly into their thumbnails.
Runes can also be engraved into the metal of a weapon or tool, carved into the door, lintel or foundations of a building, carved or painted on a container to affect whatever is in it, and so forth. For example, a grain chest might be marked with runes against decay or to keep mice out. Our local Ásatru godi has a meadhorn used for communal feasts, which he has carved with the runes for peace, accord and good fellowship - very necessary, his folk are a rambunctious lot!
