I can’t add anything to the above learned technical discussion about the chemical makeup of denatured alcohol. My understanding has always been that it’s extremely dangerous stuff to drink, and I’ve never felt any inclination to do so. Any time I’ve had a can of it in the house I’ve kept it locked up.
It does have an excellent use in traditional ship model building: it’s the standard thinner/solvent for shellac. Shellac has been around for centuries, and many modelers and woodworkers think of it as obsolete. The truth is that it’s an excellent, versatile wood finish. It is, in fact, undergoing something of a rebirth in popularity among woodworkers at the moment. Shellac is reasonably easy to apply, doesn’t cost much, and can produce a beautiful finish. (It’s also relatively non-toxic, once the denatured alcohol has evaporated. As I understand it, shellac isn’t approved for eating utensils but is approved for furniture that’s going to be used around kids.) Purist woodworkers in fact make their own shellac, buying it in the form of flakes that are diluted to the desired working consistency with denatured alcohol.
My main interest is relatively small-scale sailing ship models. Whenever I make a deck (usually out of either basswood or holly planks) I give it a light coat of stain, then a coat of shellac - diluted almost beyond recognition with denatured alcohol. The resulting finish is almost invisible, but does a great job of settling any wood grain and (most important) protecting the deck planks from any paint or other nastiness that gets spilled on them.
For such things as display cases and baseboards, shellac makes a fine, simply-applied finish. It’s currently available in several tints (white, amber, and “button,” or brown), all of which give slightly different casts to the wood. It can be applied with a natural, synthetic, or foam brush, and dries within a few minutes. Several coats of shellac can be applied in one work day, and will produce a finish that’s hard to beat in terms of appearance. (It’s not as durable as modern polyurethane or clear lacquer, but in modeling applications that may not be particularly relevant.)
Another important feature of shellac is that it’s reversible. Regardless of how long it’s been on the wood, shellac can, almost without exception, be removed by rubbing the surface with a rag that’s been soaked in denatured alcohol. This attribute is especially important in restoration work. Shellac was a common furniture (and ship model) finish in the eighteenth and nineteenth centuries. Many such pieces have “alligatored” - the shellac has gotten dirty and scaley. I’ve seen examples of old shellac that’s turned a disgusting, gritty black. A quick wipe with denatured alcohol makes it look almost like new. And because shellac is reversible, professional conservators generally approve of it as a finish for old, valuable artifacts.
A few years ago I got hired to restore some ship models for the U.S. Coast Guard Museum. One of them was a nice old model of a nineteenth-century revenue cutter. The bottom of its hull was painted copper, with some sort of clear, gloss finish on it. The paint was in fine shape, but the clear gloss had “crackled” - there were hairline cracks all over it. I puzzled for some time over what to do about this; the finish certainly looked like clear lacquer or varnish. Without thinking it would have any effect, but intending to rule out the least radical approach first, I wiped the hull gently with a rag soaked in denatured alcohol. I was pretty surprised when the “crackling” instantly disappeared, leaving a beautiful, shiny copper hull.
Yes, denatured alcohol has its uses. Just don’t drink it.