unwritable
/ˌʌnˈraɪtəbəl/Definitions
1. adjective
Unable to be written; not capable of being inscribed or recorded.
“The unwritable nature of certain materials made it impossible to record data using traditional methods.”
2. noun
Something that is unwritable; an area or material that cannot be written on or recorded on.
“The unwritable surface of the old monument made it a challenge for the archaeologists to decipher its meaning.”