Cover sinew in horn bow?

The most common material for most cultures would be birch bark. Perhaps due to the natural membrane in the material that might helps stabilizing the bow's moisture contents somewhat.

Snakeskin or other thin hides / leathers are used to good effect by some boywers as well. I don't know about parchment.

-Peter

People have told me that they have problems with parchment. another surface was paint covered in varnish. Varnishes take a long time to dry, but they can be removed and reapplied on old or surface damaged bows.