R. Horky's article does mention experimentation with various substances to produce varnish with which to form a nearly gas-tight seal, but says the best solution turned out to be "old rubber car springs dissolved in oil." This allowed Dr. Cheves to produce an excellent balloon which he brought to Richmond around June 24, 1862. Hot air was too inefficient and dangerous and hydrogen was unavailable, so they used standard illumination gas which enabled the bag to carry a single occupant up to about 1000'. (Source: Alexander, "Fighting for the Confederacy. Pp.115-16.)

Mike