Pretty sure it is shellac, dissolved in alcohol. I use it just the way others here use it, to keep fiberglass from fraying, to raise the grain and partially seal the wood prior to sanding and covering. I have not heard of using it like Bob says, to stop dope from seeping though silk and puddling...I'll have to try that!

Nice thing is that although it stinks, the smell dissipates very quickly so I can use it in my shop connected to the house without smelling up the place like dope does.

Jim