Slip Graal or slipgraal (also called Turbine Graal)
This is a variation on the Graal technique. Rather than being engraved or etched, the motive is ground onto the colored piece of glass. The slip graal pieces are usually decorated with vertical lines that are ground onto the hot glass in a circular motion. This technique was also known as Turbine Graal at Orrefors.
The bowl pictured on the left is a Slip Graal bowl made by Edvin Öhrström (Ohrstrom).
The slipgraal technique was used mainly by Edvin Ohrstrom, other designers like Edvard Hald and Ingeborg Lundin, preferred the Graal technique.
You can find all the date codes and/or serial numbers related to Orrefors Slip Graal on the following link: Dating Orrefors Slip Graal