Dope (cellulose nitrate) for rodbuilding purposes goes back to the use of silk as whipping thread. In the infancy of aviation in the 1st war, aircraft wings were covered in fabric, and something was needed to tighten this after fixing to the airframe. They used shrinking dope (there is a non-shrinking version called banana oil), and the rod-builders of the time used the same principle to tighten the silk whippings, as there was little or no stretch in silk. after it had dried, they then applied resin varnish, produced from pine trees as the final finish.
Today, forget the dope. We have NCP and non-NCP threads, NCP retain their colour when finish is applied, non-treated don't. If you just want one quick coat and then out to play, then a moisture-curing urethane is perfect. If you want a pro-finish, then the 2-pack epoxy with plasticiser is the way to go. Today, dope serves no useful purpose.
philthrod