I am a lurker, but had to add my little bit.  The nitrocellulose
treatment that they are talking about will almost for sure be
a variant of "aircraft dope", which you can buy at model and hobby
shops.  It is well known to vintage aircraft builders, model airplane
makers and also to kayak builders.  It is used to tighten and stiffen
fabrics and also makes them waterproof, while leaving them a little
flexible.

The egg-white treatment is an albumen coating, sometimes called glair
or glaire.

Purists will want to use one of these treatments; the reason they
were used was that they were available, and did the job reasonably
well, unlike shellac or hide glue.

If they had had thin silicone material such as can be bought at
McMaster Carr, they would have used it.  The same goes for rubber
tubing, which gets brittle, unlike Tygon or other tubing materials.

Gord Mawdsley