One of the most misunderstood aspects of glass is the difference between etched, cut, and engraved decoration. Simply, etching is a process using acid to essentially bubble up the surface of the glass to make a pattern on it. The two main types are plate etching and needle etching. In either case, it's easy to tell whether something is etched or cut with a wheel; the etched piece has its surface decoration in relief, the wheel cut designs are cut into the glass making them concave.
Acid has also been used by high-end companies such as Dorflinger to create "deep etching" which looks more like wheel-cut work. But the massive majority of etched glass was made for the everyman, and meant to look like the far more skill intensive and frankly expensive and beautiful engraved luxury glass.
When you look closely at the surface of a glass, if the lines are uneven, watery and bumpy, you've probably got etched. Sadly, because so few people seem to know the difference, a good 80% of what is identified as "etched" on eBay, for example, is actually wheel cut. Below are two examples of etched glass. The first one was even incorrectly identified as needle etch when it is actually plate etched. The second one is needle etch and is one of the etching styles that wasn't trying to imitate engraving. It was inexpensive, but at least it was original.
In a later post I will describe the various wheel cutting processes and how differently they manifest on the glass.