Grumbacher - Pre-Tested Oils - 150ml - Raw Sienna - Grumbacher's Pre-Tested Oil is the name of Grumbacher's professional range of oil colors. It's also the name for a philosophy that permeates the way that they manufacture all of their products.
Every tube that Grumbacher makes is tested again and again at every stage of its existence. Grumbacher's time-proven formulas are fine-tuned through independent laboratory tests as well as hands-on trial by professional artists. Grumbacher specifies the best ingredients available, putting every new one through a rigorous selection process. Grumbacher tests samples of each and every batch of raw material before they allow our vendors to make shipments. On the factory floor, they sample batches in process. And finally, even after their products are in the field, they continue to track batches and test for quality, performance and shelf life.