I was searching for a way to quickly thin some head cement so I didn’t have to drive to the store (a drive to anywhere from my house is not a short trip), and I stumbled upon Fly Anglers Online. The tying tips articles archive is a fantastic resource. It has tips for nearly everything, from making your own head cement, general proportions for dry fly components, how to store threads and tools — almost anything you can think of and a ton of things you never have.
Anyway, I ended up using some denatured alcohol to thin some lacquer based head cement that’s been here for two years. Hope I didn’t screw anything up but it seems to be working fine.