Grumbacher Pre-Tested Oils Pre-tested has long stood for professional quality oil color at an affordable price. The name itself means that it has been tested by human hands before it ever reaches the retail shelf. Each color swatch has been tested for masstone and mixability, and has been painted by hand in the USA. It is further tested by our staff for characteristics such as lightfastness, drying properties, pigment dispersion and viscosity. Draw downs are compared and formulas are altered to ensure that our customers receive the best oil color at the best price. Truly a professional paint, the majority of our colors are single pigment, and have a lightfast rating of 1-excellent. Pre-tested Professional offers artists a modern palette with superior tinting strength. Made in the USA.