I think more correctly, an Escher is likely a Thuringen, where as a Thuringen can be any of several other brands. The same vintage stone is often found with a variety of brandings on them, Escher, Boker, etc.... most were quarried in the same region, town and possibly the same hole in the ground. I had one marked Droescher with a Sears price tag on it. Under magnification all were identical.

The confusion comes from the MST stones. They occasionally have vintage Thuringens and most often "Natural Water Stones" which are from the Hunsrueck region, darker, harder, faster and often sold as Thuringens. They look grainier, with sparkly, fleck like grain to them while the real deal tends to be a dull, uniform finish ranging from light blue grey, to dark slateboard grey, to greenish yellow. They tend to be much softer.

In the interest of full disclosure I am a dealer in the Original Thuringen stones and for a short time in the MST Hunsruecks.

Tony