I've often read that the stuff we buy as denatured alcohol is "wood alcohol" and that Everclear is "corn alcohol". Is this true?
I do think I'd have a run at making my own shellac solvent if I didn't have to make corn mash and go through the fermentation process.
It isn't just a fermentation process. After your mash ferments, you distill it. The moonshiners have their secret "stills" hidden in the woods. When I worked a summer in West Virginia in the 1970s, the family I lived with warned me not to stray into the woods.
Ethanol is the alcohol in adult beverages. Everclear is a brand name of high proof grain alcohol. It has a high percentage of ethanol. The exact percentage varies depending on where you live and where you buy it, ranging from 75% ethanol (151 proof) to 95% ethanol (190+ proof). Corn is a common source for the grain in grain alcohol, but not the only one.
Methanol is toxic. Methanol is also known as wood alcohol because it used to be made from wood. (The process to extract methanol from wood was different, too.)
When you buy denatured alcohol, what you want is ethanol. Ethanol is cheap and easy to produce in large quantities. The government doesn't want you to go to your hardware store and buy gallons of cheap ethanol that you might drink instead of making shellac. It would damage the taxation and regulation regime around adult beverages that brings tax money to the government. That taxation dates back to the earliest days of the country.
To avoid taxation for hardware store ethanol that you buy, it is "denatured" by the manufacturer. They add toxins (usually methanol) to make it deadly to drink. The product is mostly ethanol; it doesn't take much methanol to make it toxic. There is no reason to denature the alcohol other than taxation and regulation.
You don't want to breathe denatured alcohol or allow it to touch your skin. There is enough methanol in it to harm you if it is absorbed through your skin. Wear gloves and avoid the fumes when you handle it.
(Related: Many companies started producing hand sanitizers to meet demand during the pandemic. Quite a few of them had to be recalled because they used toxic denatured (!!) alcohol as the active ingredient instead of ethanol.)