I am often asked about the differences between authentic sea glass and machine-tumbled glass. A true enthusiast, however, has no difficulty in determining and need only be equipped with a keen eye and a good sense of touch.
For starters, machine-tumbled or commercially produced glass has undergone the physical aspect of the rounding process in a machine, and thus exhibits the characteristics one might expect from such an experience. The shards will still look and feel like glass, but the edges will no longer be sharp. The machine is doing it's work from the outside-in.
Authentic, or genuine sea glass has spent many years, perhaps hundreds, tossing and turning in the darkest depths of the deepest oceans before coming to rest along the shorelines of the world. The difference is in the chemical make-up, and in the amount of time spent in the water undergoing the process of 'hydration'. Hydration is the process which occurs in waters where the Ph is above 7 (All of the oceans of the world!!!), and where the soda and lime is slowly drawn to the surface of the glass underwater. As this is occurring, the silica part of the structure, or the glass, microscopically chips away from the glass. The surface texture of authentic sea glass is so dissimilar from finished or tumbled glass because what you are left with on the surface of the glass after hydration are the bonding agents, soda and lime . In a nutshell, authentic sea glass is being made from the inside-out, and takes generations to accomplish.