Oil paint dries through the absorption of oxygen. This is a time-consuming process, which is why oil paint dries slowly. This can be influenced with quick-drying mediums, but not too much, so as not to disturb the drying process.
Haarlemmer Olieverf has several types of medium:
Traditional medium 1 and 2, normal drying and "fast" drying, based on turpentine. The normal drying medium hardly affects the drying process. The fast-drying medium speeds up the drying process, but without the use of siccatives.
ECO medium, an average drying medium based on Terpen10 instead of Turpentine. This medium has a less strong odor and is practically free of harmful aromatics.