Ancient's Bone Pen

A writing utensil made from the bones of Ancestral Species that roam the Dust. Once properly cleaned, they are whittled down to a rounded shape for easier handling.
As all of the species of the Dust are naturally averse to light of any sorts, their bones are weakened by it, and it left long enough can start to melt. The bones themselves are placed in a solid cover or wrap, anything is usable as long it it blocks out sun exposure. If the bare bone is left in sun for long periods of time, it will melt, then harden into a brittle paste that turns to unusable powder that can only be disposed of.
Can be used as anything from a hard pen to soft calligraphy pen.

It's most popular form, wrapped thinly with a white peelable paper, with a blunt square edge. Ready for easy usage right out the box.
Large orders can be ordered in sealed boxes unwrapped, and need to be quickly processed with a low light source, typically covered by the box's lid to avoid any damage. It can be ordered as the raw bone to change the bone to the owners preference, or whittled and ready to be wrapped.
A thicker bone with a loose rag wrapping makes for a creative brush. It requires a large light exposure to create the messy brush, and will need to be "lit" by the source every ten minutes or so to keep the consistency.

A common product sold by the Bridgeside Council.

"My bone pen was completely useless on the carriage, a blackout happened right at the beginning. The conductor hushed me when I asked if it was going to last the whole ride, he was so concerned with the monsters. A tragic waste of time!"

-Highform Poet

Because its activated by light, it's favored by the Commonform and Highform who have easier access compared to the Bridgeform who manufacture the bone. It's quickly rendered useless if there's no light source, and will harden again if left alone.
The pen will slowly be used up until it's too small and uncomfortable to use. On top of being disposable as the wrapping for the pens are often reused for the next bone pen, they can be quite inexpensive if the local Bridge Stonehouse is neraby.